Applications of Fianite in Electronics

Alexander N. Buzynin; Yury N. Buzynin; Vitaly A. Panov

doi:10.1155/2012/907560

Applications of Fianite in Electronics

Buzynin, Alexander N.;Buzynin, Yury N.;Panov, Vitaly A. 2012-12-19 00:00:00 Hindawi Publishing Corporation Advances in OptoElectronics Volume 2012, Article ID 907560, 23 pages doi:10.1155/2012/907560 Review Article 1 2 1 Alexander N. Buzynin, Yury N. Buzynin, and Vitaly A. Panov A. M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow 119991, Russia Institute for Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod 603950, Russia Correspondence should be addressed to Alexander N. Buzynin, abuzynin@yandex.ru Received 7 January 2012; Accepted 2 May 2012 Academic Editor: Jung Huang Copyright © 2012 Alexander N. Buzynin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Fianite or yttrium stabilized zirconia (YSZ) solid solutions single crystals were known worldwide as jewelry material. The review is devoted to novel applications of the material in the ﬁeld of microelectronics. A number of modern aspects of the application of ﬁanite in micro-, opto- and SHF-electronics were analyzed in this paper. It was demonstrated that ﬁanite is an extremely promising multipurpose material for new electronic technologies due to unique combination of physical and chemical properties. III V As a substrate and buﬀer layer for the epitaxy of Si, Ge, GeSi and A B compounds (GaAs, InGaAs, GaSb, InAs, GaN, AlN), ﬁanite has a number of advantages over the other dielectric materials. The use of ﬁanite (as well as ZrO and HfO oxides) instead of SiO 2 2 2 as gate dielectrics in CMOC technology seems to be of peculiar interest. The unique properties of ﬁanite as protecting, stabilizing and antireﬂecting coatings in electronics and optoelectronic devices have been outlined. A comparative study of the performance characteristics of ﬁanite and conventional materials has been carried out. 1. Introduction A number of application prospects of ﬁanite in modern electronics are considered in this paper. The further progress in electronics is connected with appli- cation of new materials. Fianite is a material of such a kind. 2. Fianite as a Substrate and Buffer Layer for Industrial technology of synthesis of ﬁanite has been for Epitaxy of Semiconductors, Multilayer the ﬁrst time developed in Russia in the Lebedev Physical Heterostructures, and Superlattices Institute of the Russian Academy of Sciences (FIAN in Russian), so the crystals were entitled after the Institute [1]. Appropriate conditions of growth of mirror-ﬂat single- Serial production of the crystals has been already started IV III V crystalline ﬁlms of A :Ge, GeSi,and A B compounds: in the early seventies of the twentieth century. Currently, GaAs, InGaAs, GaSb, InAs, GaN, AlN, and InN as well ﬁanite crystals are in the second position by the volume as multilayer InGaAlAs heterostructures and GaSb/InAs of worldwide production following silicon [2, 3]. Fianite supperlattices on ﬁanite substrates, as well as on Si and single crystals, -zirconia-based solid solutions (or “yttrium GaAs substrates coated with ﬁanite buﬀer layer, using stabilized zirconia” YSZ), were known as jewelry stone MOCVD, HW-CVD, and laser deposition techniques have imitation materials. Recently, in the countries with the been elaborated. All of these ﬁlms have been for the ﬁrst time developed microelectronics a signiﬁcant growth of interest synthesized in Russia. to various aspects of ﬁanite application in semiconductor technologies has been observed. Fianite is an extremely promising multipurpose material for new optoelectronics 2.1. FianiteasaSubstrateand Buﬀer Layer for Si, Si- III V technologies due to its unique combination of physical and Ge, and A B Compounds Epitaxy. Fianite has a number chemical properties. It can be used in, virtually, all of the of advantages as a substrate and buﬀer layer at Si and III V main technological stages of the production of electronic A B compounds epitaxy, as compared with other dielectric devices (Figure 1). materials [4–13]. 2 Advances in OptoElectronics TheﬁrstepitaxialSiﬁlmsonYSZ were grownin[6]. Fianite ZrO (HfO )−Y O The ﬁrst successful results on epitaxial MOCVD growth of 2 2 2 3 III V various A B compounds (GaAs, InAs, InGaAs, AlGaAs, GaAsN, and GaN) on YSZ are presented in a number of Epitaxy of semiconductors studies [6, 11, 12], InN on YSZ in [14, 15]. In [13, 16] Functional f ]ilms a capillary epitaxy technique—the new eﬀective way of heteroepitaxy was developed. It has been shown that the Gate dielectric Substrate Insulating Protective use of capillary forces in the method positively inﬂuences and buﬀer layer both on the mechanism of epitaxial growth and on quality Antireﬂexion of A B epitaxial ﬁlms and also reduces the minimum III V thickness of a continuous layer [16, 17]. Figure 1: Application of ﬁanite in electronics. An application of ﬁanite as either monolithic substrate or buﬀer layer in “semiconductor-on-dielectric” technology is of peculiar importance for micro- and optoelectronics. In comparison with the other dielectrics, there are the The technology allows improving such characteristics of following merits of ﬁanite in application as a substrate integrated circuits as operation speed, critical operational III V material and buﬀer layer for Si and A B compounds temperature, and radiation resistance. epitaxy: Due to a decrease of the loss of current and stray (i) High resistivity—> 10 Ohm·cm at 300 K. capacitance, energy consumption of the devices is decreas- III V ing. Moreover, the devices based on “semiconductor-on- (ii) Similarly to Si, Ge, and A B compounds, it is dielectric” structures are more reliable, especially under of cubic structure (in contrast to hexagonal of extreme operational conditions. Currently, “silicon-on- sapphire). insulator” structures are one of the most dynamically devel- (iii) It is possible to alter ﬁanite cubic lattice constant oping directions in the ﬁeld of semiconductor materials sci- in solid solutions by varying the ratio of the main ence. However, electrophysical and operational parameters (zirconium or hafnium dioxide) and stabilizing of the devices as well as its radiation resistance and reliability oxides (yttria, rare earth oxides from gadolinium signiﬁcantly suﬀer because of structure imperfection of to lutetium, and alkaline-earth oxides) that allows silicon layers. In case of “silicon-on-sapphire” structures, the an optimum matching between substrate and cubic imperfection is determined, in particular, by a diﬀerence in lattice of semiconductor ﬁlms thus improving its crystallographic structure of silicon and sapphire, as well as structural perfection. by autodoping of a silicon ﬁlm by aluminum penetrating (iv) Negligible value of diﬀusion coeﬃcients of cations from the sapphire substrate in concentrations up to 10 – 20 −3 up to 1000–1200 C temperature range that excludes 10 cm . Considering crystal-chemical and physical char- interdiﬀusion of impurities between the substrate acteristics of ﬁanite, the material is more preferential for the and ﬁlm and prevents undesirable doping (i.e., typ- epitaxy of Si as an alternative substrate in comparison with ical for sapphire), which can damage heteroepitaxial sapphire. layers through penetration of impurity atoms. (v) Due to its excellent stability at elevated temperatures, 2.2. Silicon-on-Fianite Epitaxial Structures. The ﬁrst stud- the upper limit of the corresponding structure oper- ies on silicon epitaxy on ﬁanite single-crystal substrates ational temperatures depends on physical properties have been carried out in France and USA [6, 7]. Silicon of a semiconductor only. Elevated temperature is not ﬁlms on ﬁanite substrate were deposited by chloride and critical for the substrate. hydride epitaxy at 900–1100 C. The ﬁlms obtained were (vi) Broad spectral range of transmission (260–7500 nm) of polycrystalline structure and, consequently, of rather completely covers actual absorbance and emission poor electrophysical parameters. However, at the same time, III V of Si, A B compounds and its solid solutions. it was shown that silicon-on-ﬁanite structures sustaining That makes “semiconductor-on-ﬁanite” structures actually all advantages of silicon-on-sapphire are free from very promising for the development of various its principal drawbacks. optoelectronic devices with improved operational At the epitaxy of Si on ﬁanite, a formation of SiO parameters (avalanche photodiodes, light-emitting intermediate layer between the ﬁlm and the substrate was and laser diodes, etc.). observed [7, 8]. Subsequent annealing of the structure led (vii) Application of thin layers of ﬁanite on Si and GaAs to the increase of SiO layer thickness. It was demonstrated instead of its monolithic substrates allows avoiding [8] that the layer can improve properties of silicon-on-ﬁanite spatial limitations of the structures and decreasing epitaxial structure because its formation: the net cost. At the same time, the structures on “ﬁanite/Si” and “ﬁanite/GaAs” episubstrates have better heat conductivity in comparison with the (i) removes mechanical stress in the layer-substrate structures on monolithic substrates. interface; Advances in OptoElectronics 3 (ii) smoothens over negative eﬀect occurring due to a mounted on the cooled current leads. There was a Ta plate of diﬀerence of linear expansion coeﬃcients between 80 × 5 × 0.5 mm size installed in one of the sources position. ﬁanite and silicon; Before the epitaxial growth, the sources and substrates were subjected to 10 min annealing at 1350 and 1250 C, (iii) improves insulation of the integrated circuit elements respectively, then temperature of the source was increased (ICE) based on Si; to 1380 C, as the substrate temperature was decreased to (iv) acts as a barrier for metal impurities diﬀusing from assigned values (600–700 C) and the buﬀer layer was grown. the substrate and forming deep levels in silicon. The pressure in the cell corresponded to basic one. In order to grow Ge layers, the cell was ﬁlled with GeH The formation of SiO intermediate layer at high- −3 −6 up to 1·10 –5·10 torr and the pressure was maintained temperature epitaxy is associated with peculiar properties of constant by a system of the gas feeding. Simultaneously, ﬁanite. In contrast to the other dielectrics, ﬁanite features the Ta plate situated in vicinity of the substrate was heated with a unique peculiarity as a solid electrolyte: starting to T = 1200 C. With the purpose to avoid destruction from 650 C, it becomes actually oxygen-transparent due to of germane on evaporators (Ti) following preepitaxial high mobility of oxygen. The reason for signiﬁcant mobility annealing of the sources and substrates, the sublimating of oxygen in ﬁanite crystals is an occurrence of oxygen pumps were switched oﬀ and the growth was carried out +4 +3 vacancies due to Zr to Y cation substitution at formation at pumping down using only diﬀusion- and booster-pumps. of the solid solution. High mobility of oxygen in ﬁanite It is worth to note that the gas ﬁlling up to such high crystals is determined by an occurrence of oxygen vacancies −3 pressure (∼10 torr) is impossible in MBE installations with at ZrO (HfO )–R O (here: R-Y, Gd–Yb) solid solutions 2 2 2 3 electron-beam heating. Germane pressure in the cell was +4 +4 +3 formation due to Zr (Hf )toR cation substitution. The tentatively assigned by ionization vacuum gage indications. process results in oxygen nonstoichiometric ZrO (HfO ) 2 2 Nevertheless, this peculiarity in GeH pressure measurement based phase [4]. Because of the high mobility of oxygen did not impede the controlled growth of Ge ﬁlms at at high temperature of the epitaxy (900–1000 C) used in 700–750 C temperature of the substrate. The ﬁlms were [6–8], the formation of ether SiO continuous layer or its continuous and homogeneous. GeSi solid solutions with islets between the substrate and the ﬁlm was shown to be up to 80% Si content were also obtained on (111) and inevitable. (100) ﬁanite substrates. Vacuum annealing at 1250 C during The phenomenon occurs even at the epitaxy initial stages 10 min was used as a preepitaxy treatment. The growth when a continuous epitaxial ﬁlm is forming. It was shown [9] −4 was carried out under 5·10 torr germanepressureand at that the formation of SiO layer or isles at the initial stage of 600 C substrate temperature. Simultaneously, the Ta plate molecular-beam epitaxy on ﬁanite results in 3-dimensional positioned in vicinity of the substrate was heated to 1200 C. mechanism of growth, formation of structural defects and The heteroepitaxial Ge ﬁlms obtained show high structural hindered the synthesis of Si ﬁlms of single-crystal structure. perfection. X-ray rocking curve (XRC) FWHM values were The occurrence of the isles at the initial epitaxy stages and 0.31 for Ge ﬁlm. The surface morphology of the Ge epitaxial the polycentric growth of Si layers were shown possible to layers grown on (100) and (111) ﬁanite substrates as well as avoid only by using a set of techniques, those which prevent −1 the peaks of Raman scattering near 300 cm are identical to diﬀusion of oxygen from the substrate to the ﬁlm at the those of bulk Ge. Therefore, it is possible to conclude that initial stage of the process. In particular, high structural there are no stains in the Ge/ﬁanite layer. perfection of the Si-on-ﬁanite ﬁlms was achieved by using a low-temperature (T< 650 C) molecular-beam epitaxy [7]. III V 2.4. Epitaxial Films of A B on Fianite. Crystallochemical and physical properties of ﬁanite are favorable not only for 2.3. Ge and GeSi Films on Fianite Substrates. Growth of III V silicon but also for A B compounds epitaxy (Table 1). Ge and Ge-Si heterostructures on ﬁanite substrates was III V carried out using HWCVD installation. Base pressure in the First successful results on growth of A B compound −8 chamber ∼1·10 torr was maintained by pumping-down epitaxial ﬁlms on ﬁanite substrates were presented in [10, III V using two heteroionic pumps. A high-vacuum gate was used 18]. GaAs, InAs, GaN, and other A B semiconductor for isolation of the growth cell and the pumps from other compound ﬁlms have been grown on ﬁanite, as well as parts of the vacuum system. Forepumping of the chamber on silicon and gallium arsenide with ﬁanite buﬀer layer was performed using a diﬀusion pump. The diﬀusion pump substrates by means of metal-organic chemical vapor deposi- allowed to exhaust any gas (including GeH )bothinatomic tion (MOCVD). A new eﬃcient epitaxy technique-“capillary and molecular state. FM-1 oil with low vapor pressure was epitaxy” has been suggested. The technique allowed synthe- III V used as a pressure ﬂuid. There was a nitrogen trap above sizing of A B compound ﬁlms by a MOCVD on ﬁanite the diﬀusion pump preventing reverse diﬀusion of the oil substrates. Samples of structurally perfect submicron (up III V from preevacuation and diﬀusion pumps into the growth to 0.1 μ) epitaxial ﬁlms of A B compounds have been cell. The (100) and (111) oriented ﬁanite single-crystal plates obtained using this technique. The samples demonstrated were used as substrates. Silicon atomic beam was maintained high electrophysical parameters [13, 17–20]. In [21], GaN by sublimation of the element single-crystal (high resistance) epitaxial ﬁlms have been grown on ﬁanite substrates by in form of 4 × 4 × 90 mm ingot sections. The sources were MOVP technique. It was observed that the epitaxial growth 4 Advances in OptoElectronics III V Table 1: Some properties of ﬁanite crystals and A B compounds. Lattice −6 −1 T , C (melting point) Crystal Thermal expansion coeﬃcients 10 deg E ,eV Type a, A 5.141 (x = 10) (ZrO ) (Y O ) Cubic (ﬂuorite) 2800 11.4 (15–1000 C) 2 2 3 5.157 (x = 15) 100−x x 5.198 (x = 21) GaAs Cubic (sphalerite) 5.65 1283 5.4 1.43 GaP Cubic (sphalerite) 5.445 1467 4.7 2.26 a = 3.186; GaN Hexagonal (wurtzite) 1700 5.6; 7.8 3.4 c = 5.178 GaN Cubic (sphalerite) 4.52 1700 3.9 3.2 a = 3.54 InN Hexagonal (wurtzite) 1200 12.7 0.7 c = 5.70 InN Cubic (sphalerite) 1200 4.4 0.67 4.98 of GaN on ﬁanite signiﬁcantly depends on conditions of the leading to growth according to the Volmer-Weber mecha- initial stage of the process. nism. Formation of the continuous layer occurred through 3-dimensional nuclei, their subsequent growth and joining. In [11, 22, 23], ﬁanite substrates were successfully tested Low nuclei density results in the formation of highly inho- for growth of InN heteroepitaxial ﬁlms. InN ﬁlms of cubic mogeneous rough surface that hinders subsequent formation structure have been grown on (001) ﬁanite substrates by of a ﬂat ﬁlm. A laser sputtering technique is considered to plasma-stimulated molecular-beam epitaxy (RF-MBE) at maintain high nuclei density; so, before joining, the nuclei 400–490 C temperature. The lattice mismatch of InN and are of suﬃciently small size that promotes the formation of a ﬁanite at (001) plane is very low (less than 2.3%), in contrast ﬂat continuous ﬁlm. to 17% for InN sapphire and more than 10% for InN-GaAs. Due to this fact, InN ﬁlms grown on (001) ﬁanite substrate Therefore, in order to obtain ﬂat layers, a laser sputtering were superior InN ﬁlms grown on sapphire [10] and (001) technique was used in the study. GaAs substrates by its crystallographic perfection [15]. The Q-switched Nd laser and single-crystal GaAs and Therefore, ﬁanite is apparently in advance as a substrate InAs targets were used. The superlattices were grown by for InN epitaxy as compared to sapphire. A new eﬀective optical switching of the laser beam between the targets. method of heteroepitaxy, capillary epitaxy, was proposed Mirror-ﬂat GaSb and GaAs:Sb layers as well as penta- in [17]. In particular, this technique allows us to obtain periodic InAs/GaSb supperlattices of 0.15 μm total thickness III V the ﬁlms of A B compounds on ﬁanite using a MOCVD were deposited using this technique. approach. The X-ray diﬀraction investigations of GaAs:Sb (111) ﬁlms on ﬁanite (111) showed their single-crystal structure (Figure 2(a)). It was shown that the spectral dependence 2.4.1. Deposition of GaAs, GaSb, GaAs:Sb Films, and GaSb/ of photoconductivity of GaSb ﬁlms on ﬁanite substrates InA Superlattice on Fianite Substrates by Means of Laser (Figure 2(b)) has a maximum of photoconductivity at the Sputtering. Our experiments have shown that the conven- edge of fundamental absorption. This eﬀect may be due to tional “direct” growth of heteroepitaxial InGaAs ﬁlms on high velocity of the surface recombination. ﬁanite substrates resulted in the ﬁlms with rough surface. The X-ray rocking curve (XRC) FWHM value was 0.23 So the buﬀer layers were elaborated to improve the results. The buﬀer layer must have very high structural perfection for GaSb (111) ﬁlm. The image of the surface of GaAs:Sb (0.2 μm thickness) on ﬁanite is shown in Figure 3(a).Itisappar- and mirror-homogeneous surface. A number of experiments ent that the surface of the layer is mirror ﬂat and suﬃciently were conducted for growth of GaAs, GaSb, and GaAs buﬀer layers on ﬁanite (100) and (111) substrates as well homogeneous. The microrelief of the layer surface is shown in Figure 3(b). According to our estimations, roughness of as GaSb/InAs superlattice by using laser sputtering. This superlattice is working as a ﬁlter, which prevents penetration the layer is less than 4 nm (Sq = 0.003778 μm). of the defects into InGaAs ﬁlm and, ﬁrst of all, formation of In the penta-periodic InAs/GaSb supperlattices of growing dislocation. Furthermore, Sb is an eﬀective surfac- 0.15 μm total thickness grown on (111) ﬁanite substrates tant which signiﬁcantly improves the ﬁlms morphology. electron mobility approaches to 580 cm /V × s. The GaSb The studies have shown that it was complicated to obtain layers, as well as InAs/GaSb short-period supperlattices, are III V thin and homogeneous layers of A B compounds on ﬁanite suitable for the development of IR detectors operating in substrates. It may be related to rather high mismatching a2-3 μm range. In our studies, the structures were used as III V III of the lattice parameters of ﬁanite and A B compounds buﬀers for A N growth on ﬁanite substrates. Y : 99.2 μm Advances in OptoElectronics 5 Measurement of GaSb photoconductivity, 2.5 Si–ﬁlter XRD–spectra Z5551S Z5551S 1.5 0.5 1.2 1.3 1.4 1.5 1.6 1.7 1.8 24.5 25 25.5 26 26.5 2θ (deg) λ (mkm) (a) (b) Figure 2: XRD θ/2θ scan of GaSb (111) ﬁlm on ﬁanite (111) (a) and photoconductivity of GaSb ﬁlm on the ﬁanite substrate (b). 3D surface 606.52 Length = 69.81 μm; Pt = 6.064 nm; scale= 10 nm −2 −4 Azimuth: 66.3 (deg); elevation: 40.7 (deg) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 X scale: 1; Y scale: 1; Z scale: 1 (μm) (a) (b) Figure 3: Image of surface (a) and the surface relief (b) of GaAs:Sb buﬀer on ﬁanite. 2.4.2. MOCVD Capillary Epitaxy of III-V Compounds on growth stages showed that the transition from conventional Fianite. The investigations showed that continuous GaAs MOCVD growth to capillary epitaxy leads to a change in the ﬁlms on ﬁanite can be obtained only in a very narrow growth mechanism. Three-dimensional island mechanism range of the epitaxial conditions. In particular, a temperature changes to the two-dimensional one with propagation of range of 550–600 C is necessary. The minimum thickness the growth steps (Figure 4(a)). This process is similar to of a continuous layer was 1.5–2.0 μm. The epitaxial ﬁlms graphoepitaxy [24, 25] from aqueous solutions with addition had polycrystalline structure and rough surface. Structural of surfactants, where an increase in the substrate wettability and electrical properties of GaAs ﬁlms could be improved also signiﬁcantly improves the quality of graphoepitaxial using capillary epitaxy. The essence of this method is that layers [24](Figure 4(b)). a thin (less than 50 nm) ﬁlm of an III-group element is In both cases, the height of the crystallization medium initially deposited on ﬁanite surface and then saturated (melt or solution) decreases in the initial stage due to the with a V-group component with the formation of a thin capillary forces. This eﬀect impedes growth of epitaxial continuous epitaxial III-V layer. Following this procedure, nuclei in the direction normal to the substrate surface the ﬁlm growth continues to obtain the necessary thickness and facilitates their growth in the tangential direction. under conventional epitaxial conditions. As a result, the substrate orienting role increases and a The use of capillary forces in the ﬁrst (heteroepitaxial) transition to the layer-by-layer growth mechanism occurs stage of GaAs ﬁlm formation led to improvement of epitaxial with a decrease in the growth step height. Consequently, the quality. Electron microscopy of the GaAs ﬁlms at the initial minimum height of the continuous ﬁlm decreases and the :98.41 μm S (a.u.) (nm) (nm) 6 Advances in OptoElectronics (a) (b) Figure 4: Analogy between the capillary epitaxy and graphoepitaxy. (a) Electron microscopy image of GaAs on YSZ at the initial stage of growth (20000x): conventional MOCVD, height of the islets is up to 3000 nm. (b) The capillary epitaxy technique, minimal layer thickness is 50 nm, the layer growth is visible [18]. Optical microscopy image of NH J on amorphous Al graphoepitaxy growth: without (c) and with (d) the use of surface-active substances, magniﬁcation 100x [24]. ﬁlm structural quality is improved. It has been shown that Mobility Transistor) for microwave frequency FET operating the use of capillary forces in this technique improved both in 10–40 GHz range (Table 2) using “Aixtron AIX 200RF” III V the mechanism of epitaxial growth and quality of A B installation. Capillary epitaxy MOCVD technique in 550– epitaxial ﬁlms. It also reduces the minimum thickness of 600 C temperature range was used. acontinuouslayer [14, 18]. Virtually the same approach Grown by the “capillary epitaxy” technique series of III to deposition of A N ﬁlms on various substrates has been GaSb and GaAs:Sb buﬀer layers on (111) and (100) ﬁanite successfully applied in studies of the other authors [26]. substrates were developed to decrease surface roughness The use of capillary epitaxy made it possible to decrease of the PHEMT heterostructure. The buﬀer layers had a minimum thickness of a continuous GaAs/ﬁanite ﬁlm to uniform mirror-smooth surface of about 5 nm roughness. 25 nm and to improve its structural quality and surface Application of the developed buﬀers made it possible morphology. The technique was also eﬃcient for growing of to obtain an AlGaAs/InGaAs/GaAs heterostructures with III V the other A B compounds on ﬁanite. uniform mirror-smooth surface on ﬁanite substrates and to decrease its roughness by a factor of 10 (to 25 nm). 2.4.3. Deposition of GaAs, AlGaAs, and InGaAs-Based Multi- As a result, suﬃciently homogeneous AlGaAs/InGaAs/GaAs layer Structures on Fianite. The results on epitaxial growth multilayer heterostructures with smooth slightly bloom III V of A B compound ﬁlms obtained in the studies described surface were grown on (001) ﬁanite substrates of 50 mm above were used for obtaining of AlGaAs/InGaAs/GaAs diameter. Roughness of the heterostructure surface mea- multilayer heterostructures on ﬁanite. These structures were sured using Talysurf interference microscope (3-dimensional III V used in FET. Sequential growth A B heteroepitaxial lay- topography) was 0.25 μm. This structure was grown using ers on ﬁanite substrates was conducted according to the “AIXTRON” installation on (100) ﬁanite ellipsoidal substrate topologic scheme of PHEMT (Pseudomorphic High Electron of 2 inch major diameter. The surface of the multilayer Advances in OptoElectronics 7 Table 2: PHEMT heterostructure for FET operating in 10–40 GHz crystallochemical parameters and high chemical stability. range. Besides ﬁanite, Si and GaAs substrates with ﬁanite buﬀer layer were developed in scope of the work. Synthesis of the + 18 −3 n GaAs:Si n ∼ 6 × 10 cm 40 nm Si layer was carried out by a laser deposition technique. The i-Al Ga As x ∼ 0.24 (>0.23) 25 nm x 1−x growth of ﬁanite ﬁlms on silicon substrates was conducted i-GaAs ∼0.6 nm with the purpose to evaluate prospects of the use of less −2 δ-Si n ∼ 4.5 × 10 cm Si expensive large silicon substrates with ﬁanite sublayer instead i-GaAs ∼0.6 nm of monolithic ﬁanite because maximum dimensions of the i-Al Ga As x ∼ 0.24 4 nm silicon-on-ﬁanite structures are limited by size and quality of x 1−x i-GaAs 1 nm ﬁanite crystals and the corresponding substrates (currently ∼50 mm). i-In Ga As y ∼ 0.18 (<0.2) 11 nm y 1−y Another purpose of the study was determination of i-GaAs 30 nm suitability of ﬁanite not only as a substrate material but i-Al Ga As x ∼ 0.24 50 nm x 1−x 14 also as a gate dielectric. Production of such substrates −3 i-GaAs n< 8 × 10 cm 0.5–0.8 μm will allow integrating GaN-based optoelectronics with a CP AlAs/GaAs (1nm/2nm) × 5 well-developed silicon and gallium arsenide electronics and GaAs:Sb 100 nm optoelectronics. Fianite substrate 400 μm GaN Films on Fianite Substrates. Growth of the ﬁlms on (111) and (100) oriented ﬁanite substrates was carried out structure is rather uniform but its roughness reaches the using nucleus layers. 3 types of the nucleus layers were used: value of 25 nm. Structural perfection of AlGaAs/InGaAs/GaAs multi- (1) low-temperature GaN nucleus layer with annealing layer heterostructures on ﬁanite was investigated by means in hydrogen-ammonia atmosphere; of XRD. DRON-4 device (Ge(004) monochromator, CuKα1 (2) low-temperature AlN nucleus layer with annealing in radiation) was used. Θ/2Θ spectra were recorded at sym- hydrogen-ammonia atmosphere; metric reﬂection mode by scanning with 0.1 step of the (3) high-temperature AlN nucleus layer. texture maxima rocking. X-ray diﬀraction Θ/2Θ spectrum of GaAs (001)/ﬁanite (001) is shown in Figure 5. The peaks of At the use of all of the types of the nucleus layers, ﬁanite (Zr,Y)O (004), 2θ = 73.4 substrate and of GaAs (004), 2θ = ◦ substrates were annealed in pure hydrogen at ∼1070 C 66.05 buﬀer layer were recorded. The width of the layer before deposition of the ﬁlms. rocking curve FWHM = 1, that is, the evidence of a mosaic ◦ Hydrogen is a conventional carrier gas in MOGPE of structure of GaAs layer. The grain-boundary angle was ∼1 . III-V materials because it can be rather readily puriﬁed. The use of (111) ﬁanite substrates with GaAs:Sb buﬀer layers Similarly, in MOGPE of nitrides of III group hydrogen for for deposition of AlGaAs/InGaAs/GaAs heterostructures on the ﬁrst time was used as a carrier gas. However, later it was ﬁanite resulted in the formation of mirror-ﬂat homogeneous demonstrated that in contrast to classic III-V semiconduc- surface and 10-fold decrease of the surface roughness (up to tors, GaN and InN are unstable under hydrogen atmosphere 0.025 μm). and undergo destruction (etching) at the temperatures used Detailed data on elemental and molecular composi- for growth of these crystals. This is an evidence for hydrogen tions of the heterostructures were obtained by means of as a carrier gas at the epitaxy of nitrides of III group elements layer-by-layer SIMS (“TOF SIMS-5” spectrometer). The actively participates in the process occurring on the surface sputtering was carried out by Cs , 2 keV, raster 250 × of the growing ﬁlm, in contrast to GaAs. Therefore, in 250 μm, negative ion detection mode, the probe beam Bi , most cases for growth of nitrides of III group by MOGPE, 25 keV, and depth resolution DZ > 7 nm. The analysis ammonia is used as a nitrogen source and supplied into of the AlGaAs/InGaAs/GaAs heterostructures obtained on reactor in large quantities. For a long time, ammonium was ﬁanite (Figure 5(b)) has shown that its inner topology was of opinion that it inhibits the destruction of a growing ﬁlm in conformity with the assigned scheme (Table 2) of the and makes the eﬀect of hydrogen negligible. However, it PHEMT structure. appears that it is far from the case and hydrogen signiﬁcantly inﬂuences the process of the nitrides growth. III 2.4.4. A N Films on Fianite Substrates and Buﬀer Layers. The studies have shown that at annealing of LT-GaN Principal diﬃculty of growth of perfect heteroepitaxial GaN nucleus layer, the latter undergo etching in H -NH ﬂow 2 3 ﬁlms is an absence of suitable substrates having good match- hindering growth of a high-quality GaN ﬁlms. Application ing with the heteroepitaxial ﬁlm. Currently, for the growth of of the low-temperature AlN nucleus layer with annealing GaN ﬁlms, Al O , ZnO, MgO, SiC, Si, and GaAs substrates in hydrogen-ammonia atmosphere as well as the high- 2 3 are in use. Usually, a material with wurtzite structure is temperature AlN nucleus layer on (111) and (100) oriented grown on a hexagonal substrate, whereas sphalerite is grown ﬁanite substrates resulted in formation of hexagonal GaN on a cubic one. Fianite as a substrate material for cubic ﬁlms comprising a textured polycrystal of hexagonal mod- InGaN epitaxy has a number of advantages, such as favorite iﬁcation. Scattering angles of the texture for the GaN ﬁlms 8 Advances in OptoElectronics n GaAs: Si AlAs/GaAs InGaAs AlGaAs GaAs: Sb YSZ XRD–spectrum i-GaAs AB7A % (C) % (O) % (As) ### % (AlAs) % (SiAs) % (Zr) % (GaAs) % (SbAs) % (InGaAs) 66 67 68 69 70 71 72 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2θ (deg) Depth (mkm) (a) (b) Figure 5: XRD θ/2θ scan (a) and layer-by-layer secondary ion mass-spectrometry (b) of AlGaAs/InGaAs/GaAs (001)/ﬁanite (001) multilayer heterostructure. grown on the (111) and (100) oriented substrates were 10 XRD–spectra H1058B/YSZ111 and 15 ,respectively. H1058B YSZ100 It has been shown that high-temperature annealing of LT-GaN buﬀer layer at 1000–1100 C promotes improvement of structural perfection GaN heteroepitaxial ﬁlms. The GaN layers on ﬁanite substrates exhibited an intense photolumi- nescence with maximum at 365 nm. The conditions of growth of single-crystal GaN ﬁlms on (111) and (100) ﬁanite substrates by MOCVD without buﬀer layer at 850 C substrate temperature have been determined. The spectra of θ/2θ scanning were obtained using Ge (400) monochromator (Figure 6). Two peaks of the substrate were observed at 30 YSZ 29 30 31 32 33 34 35 36 37 (111) and 34.8 YSZ (200). The ﬁlm provides a single GaN 2θ (deg) (0002) peak at 34.5 . Since GaN (0002) peak is close to Figure 6: XRD θ/2θ scan of GaN ﬁlms on (111) and (100) ﬁanite YSZ (200) one, a narrow slit in front of the detector was substrates. inserted with the purpose to increase the resolution. GaN hex (0001) was detected on both substrates at FWHM of the XRC < 1 that corresponds to the epitaxial growth. Traces of temperature. Before the deposition of AlN ﬁlms, ﬁanite the polycrystalline phase at 32.4 (expected 0.1–1.0 intensity substrates were annealed in pure hydrogen at ∼1070 C. units) were not detected. Mirror-ﬂat homogeneous AlN ﬁlms with the roughness not exceeding 0.6 nm (Figure 7) were deposited on (100) and AlN Films on Fianite Substrates. The AlN ﬁlms on ﬁanite (111) ﬁanite substrates. substrates were grown using an MOGPE technique. The Layer-by-layer analysis of AlN nucleating layer on the Al Ga N direct gap semiconductors are very useful in the x 1−x ﬁanite substrates was carried out by SIMS using TOF SIMS-5 development of UV photodetectors. By altering Al content device (sputtering by Cs+, 2 keV, 250 × 250 raster, negative in GaN-based solid solutions, it is possible to obtain the recording mode, Bi+ probe beam 25 keV). material with a forbidden band ranging 3.43–6.2 eV thus The study has shown that the ﬁlms had uniform distribu- covering 200–365 nm spectral band. This spectral band tion of its constituents, the concentration proﬁle of Zr atoms is of practical importance in UV astronomy, ozone layer at the heterointerface being very sharp (Figure 7(c)). The use monitoring, combustion, and water sensors. These ﬁlms are of AlN nucleating layers on the ﬁanite buﬀering layers allows both of original interest as well as are useful as nucleating and deposition of continuous and homogeneous GaN ﬁlms of buﬀer layers in GaN epitaxy. hexagonal modiﬁcation. Growth of the ﬁlms was started from thin 20–50 nm nucleating layer. Two growth modes were used: at 650 C with subsequent annealing in ammonia-hydrogen media at Deposition of InN Single-Crystal Films on YSZ Substrates by 1100 C during 30 min followed by growing up of the basic Means of LP-MOCVD Technique Using Pulse-Capillary Epi- layer and high-temperature growth of AlN at the same taxy. InN heteroepitaxial ﬁlms attract a signiﬁcant interest Intensity (cps) Advances in OptoElectronics 9 Length = 101 μm; Pt 2.825 nm; scale= 5nm −0.5 5.854 nm −1.5 −2.5 101 μm 101 μm −3.5 −4.5 0 1020 30 40 50 6070 80 90 100 (μm) (a) (b) H1005B1 Cs 2 keV AlN/ZrO 0 100 200 300 400 500 Sputtering time (s) C 3 O Zr Al ZrO AlN (c) Figure 7: Image of surface (a) and the surface relief (b) (Interference Microscope “Talysurf ”); results obtained by layer-by-layer SIMS analysis (c) of the low temperature AlN layer on ﬁanite substrate (TOF SIMS-5). because the ﬁlms provide an opportunity of the development In [5], InN epitaxial ﬁlms have been for the ﬁrst of high-frequency electronic devices. Since an industrial time deposited on ﬁanite substrates by pulse-capillary LP- technology of InN substrates production is so far absent, MOCVD. The technique was shown to allow a signiﬁcant improvement of the ﬁlms quality, as well as synthesizing heteroepitaxial growth of InN on foreign substrates is single-crystal InN ﬁlms of hexagonal modiﬁcation. The required. Al O and Si substrates, being well developed and 2 3 ﬁlms demonstrated rather perfect morphology along with having considerable dimensions along with excellent crystal high photoluminescent and electrophysical characteristics. perfection, seem to be of the most interest. Moreover, Si is The structures on ﬁanite substrates were grown under low not expensive and allows a combination of the InN-based pressure in vertical reactor supplied with rotating molyb- devices with well-developed silicon electronics. However, denum stand (designed in IPM RAS). The substrates were mismatching between Al O , Si, and InN lattice constants is 2 3 inductively heated, trimethyl indium (TMIn) and ammonia rather large, 25% and 8%, respectively. That was the reason were the element sources, and nitrogen was the carrier why ﬁanite (YSZ) has been recently taken into account as an gas. The substrates of (111) and (100) orientations were alternative substrate. used. Comparative studies of the InN ﬁlms were carried For the ﬁrst time ﬁanite substrates have been successfully out using optical and electron microscopy, SIMS, XRD, tested for deposition of InN heteroepitaxial ﬁlms in [4]. photoluminescence, and probe techniques. The ﬁlms of cubic symmetry were grown on (001) ﬁanite The experiments on deposition of InN ﬁlms on ﬁanite substrates using plasma-assisted molecular beam epitaxy by MOCVD technique have shown that it was diﬃcult to (PA-MBE) at 400–490 C. grow a uniform and smooth InN ﬁlm using general growth Due to better crystal-chemical matching between InN process, as well as single-step capillary epitaxy, because of and ﬁanite, the ﬁlms grown on ﬁanite substrates exhibited three-dimensional nucleation. Satisfactory results have been crystal perfection better than those grown on sapphire and achieved only by using pulse-capillary epitaxy, in which the GaAs substrates [4]. process of intermittent supply of In (in form TMIn) at Intensity (cps) (nm) 10 Advances in OptoElectronics (a) (b) Figure 8: Morphology of the surface of InN ﬁlms deposited by means of conventional (a) and pulse-capillary LP-MOCVD techniques (b) (scanning electron microscope Supra 50 VP). constant NH ﬂow was repeatable [7]. The pulse-capillary XRD–spectrum LP-MOCVD deposition was started by puﬃng TMIn in H1142A nitrogen without ammonia inﬂow during 20 s followed by 40 s interruption of TMIn supply and puﬃng nitrogen- ammonia mixture. TMIn ﬂow was equal to 0.25 sccm/min. The procedure was repeated ten times and then the growth of InN ﬁlm was conducted at 550 CinN -TMIn-NH gas 2 3 5 6 mixture. The V/III reactant ratio was in the range of 10 –10 . Under these conditions growth of InN ﬁlms of 0.3 μ thickness was observed. The application of “pulse-capillary epitaxy” technique and ﬁanite substrates resulted in the formation of mirror-ﬂat ﬁlms of single-crystal structure. The comparative studies on growth (nucleation and formation of the primary 30 31 32 33 2θ (deg) continuous layer) of InN ﬁlms on ﬁanite substrates by means of LP-MOCVD and conventional MOGPE techniques have Figure 9: XRD θ/2θ scan of the InN ﬁlm. demonstrated signiﬁcant diﬀerences in size, habitus, and concentration of the epitaxial nuclei, as well as in mor- phology of the epitaxial layers. Raster electron microscopy and LP-MOCVD using pulse-capillary epitaxy are 1.0 (Supra 50 VP) images of the surface of InN layers deposited and 0.19 (curves 2and 1on Figure 10), respectively. It by means of conventional LP-MOCVD (a) and pulse- is noticeable that the latter value is considerably lower. capillary LP-MOCVD techniques (b) are shown in Figure 8. Therefore, the growth on ﬁanite results in more structurally Roughness of the surface of InN layer of 0.3 μ thickness perfect InN ﬁlms due to better crystallographic matching, grown by the conventional technique is apparently seen. other conditions being equal. Herewith, application of the The roughness occurred because of the three-dimensional pulse-capillary epitaxy allows achieving of record values that nucleation. is the evidence of excellent perfection of InN ﬁlms obtained At the same time, pulse-capillary epitaxy resulted in more in this study. smooth and uniform surface. θ/2θ scanning spectrum of InN The nondoped epitaxial InN ﬁlms grown on ﬁanite sub- ﬁlm deposited on (111) ﬁanite substrate by pulse-capillary 19 3 strates were semiconductors of n-typewith2.5 ∗ 10 cm LP-MOCVD technique and rocking curves of InN ﬁlms are electron concentration. It is also noticeable that Hall mobility presented in Figure 9. The 2θ peaks in the spectrum are value approaches 320 cm /V × s. The ﬁlms showed intense attributed to 30.0—YSZ (111) substrate, 31.3—InN (0002) photoluminescence with peak maximum at 0.87 eV. layer, and 33.0—In (100). The rocking curve of InN (0002) ﬁlm deposited on YSZ substrate by means of pulse-capillary epitaxy is shown in 2.4.5. Electrically Active Defects in GaN Films on GaAs Figure 10. Rocking curves of InN ﬁlms deposited on YSZ Substrates with Fianite Buﬀer Layers. Comparative studies and sapphire substrates by means of conventional techniques of density and electric activity of structural defects in are shown for comparison. The rocking curve data of InN GaN epitaxial ﬁlms grown on GaAs substrates with various (0002) peak provide full width at half maximum 1,8 for buﬀer layers were carried out by an induced bias technique the ﬁlms grownonsapphire(curve3on Figure 10). The (IBT). The technique has been developed rather recently values obtained for ﬁanite ﬁlms grown using conventional [27, 28]. It is a contact-free similarity of the induced current Advances in OptoElectronics 11 optoelectronics. However, there are three considerable prob- lems occurring at GaN epitaxy: ﬁrst, a signiﬁcant parameter mismatch of GaN layer and Si or GaAs substrates; second, the diﬀerence of thermal expansion coeﬃcients of the layer and the substrates and third, insuﬃcient chemical and thermal stability of the substrates at the epitaxial temperature. Application of various buﬀer layers, in particular, ﬁanite- based, canbeaneﬃcient method for solution of the above problems. GaN epitaxial ﬁlms were grown by MOCVD tech- nique using capillary epitaxy on Si and GaAs substrates with various buﬀer layers. Trimethylgallium (TMG), arsine (AsH ), and ammonia (NH )wereusedasGa, As,and N 3 3 8 10 12 14 16 18 20 sources, respectively. Single (ﬁanite, layer of porous Si, or ω (deg) GaAs material) and double (ﬁanite on porous Si and GaAs) were tested. The ﬁrst “prominent” porous buﬀer layer was suggested to allow decreasing thermoelastic strains in the second heteroepitaxial buﬀer thus improving its morphology Figure 10: Rocking curves of (0002) InN. and structure. The upper buﬀer layer, being chemically stable in the growth medium, provides ﬁne matching with functional heteroepitaxial ﬁlm. The epitaxial structures were studied using a set of technique (EBIC-mode). IBT is a nondestructive contact- techniques: photoluminescence (PL), scanning electron free method for diagnostics of semiconducting materials and microscopy in electron-beam induced current (EBIC-mode), microelectronic devices. IBT is based on detecting voltage (or and secondary-ion mass spectroscopy (SIMS). charge) generated by an electron probe of scanning electron It was established that the use of ﬁanite buﬀer layer microscope (SEM). Draft scheme of the method is shown in on Si substrate prevents formation of amorphous silicon Figure 11(a). nitride. The GaN ﬁlms grown on Si substrates with ﬁanite The electron probe (e) scans the surface of a crystal buﬀer layer were of hexagonal modiﬁcation (α-GaN) and under the study (O). Metal ring (D), in which the surface had mosaic single-crystal structure. It was demonstrated that charge generated by electrons through capacitive coupling the use of porous Si in the complex ﬁanite/Si buﬀer allows is induced, is a detector of a signal. The signal from the improving the adhesion of GaN ﬁlm and its uniformity by ring electrode is monitored in the SEM display (or by other phase composition and thickness. measurement equipment) through charge-sensitive ampli- Layer-by-layer SIMS analysis of GaN ﬁlms grown on Si ﬁer (PA) (Figure 11(a)). The technique allows qualitative and GaAs substrates with ﬁanite buﬀer layers has shown monitoring of semiconductor plates, structures, and devices that ﬁanite layer serves as a barrier for diﬀusion of Si and identifying electric active inhomogeneities such as disloca- As into GaN ﬁlm from Si and GaAs substrates, respectively tions, stacking faults, microfractures, extent of doping by (Figure 13). Good insulating properties of ZrO in the various dopants, all p- n junctions, and Schottky barriers (see 2 double buﬀer provide an opportunity to use “Semiconductor e.g., Figures 11(b) and 11(c)). Quantitative measurements of on dielectric” technology, which is promising to improve the local fundamental characteristics of semiconductors are also integration level. possible (diﬀusion distance, nonequilibrium carrier lifetime, its surface recombination rate, diﬀusion barrier height). Comparative studies of PL spectra (recorded at 300 K) The studies have shown that the use of GaAs substrates of GaN ﬁlms grown on a monolithic GaAs substrate and with porous GaAs layer resulted in a decrease of the electric GaAs substrates with various kinds of buﬀer layers have been activity of structural defects in the GaN ﬁlms and in an carried out (Figure 14): 1 single buﬀer “porous GaAs;” 2 increase of its electrical uniformity as compared to GaN double buﬀer “ﬁaniteonporousGaAs.” ﬁlms grown on monolithic GaAs substrates. The use of The position of PL peaks in the spectra corresponds to GaAs substrates with double buﬀer layer (ﬁanite on porous characteristic peak of cubic GaN. Consequently, the use of GaAs) allows additionally decreasing concentration of the single buﬀer layerofporousGaAsaswellasdoublebuﬀer electrically active defects in GaN ﬁlms to more than an order layer (ﬁanite on porous GaAs) allows growing GaN ﬁlms of of magnitude (Figure 12). cubic modiﬁcation. The growth of GaN ﬁlm on monolithic GaAs substrate in contrast resulted to the formation of hexagonal modiﬁcation. 2.4.6. GaN Films on Si and GaAs Substrates with Fianite Buﬀer Layers. Silicon and gallium arsenide are promising III substrates for GaN and the other A N epitaxy due to 3. Functional Fianite Films their high quality, large dimensions, and a low net cost, as well as possibility to integrate GaN-based devices with 3.1. Functional Fianite Films on Si, Ge, and GaAs Substrates. well-developed silicon and gallium arsenide electronics and Thin ﬁlms of ﬁanite and related solid solutions such X-ray intensity (a.u.) 12 Advances in OptoElectronics PA (a) 20 kV x10000 1 μ 20 kV x10000 1 μ (b) (c) Figure 11: Outline of the induced potential technique (a) and scanning electron microscope images of electrically active polygonal defects in GaAs ﬁlms: secondary-electron emission mode (b); b-induced potential mode (c). 20 kV x1000 10 μ 20 kV x1000 10 μ (a) (b) Figure 12: Electrically active defects in GaN ﬁlm on GaAs substrate with buﬀer layers: (a) single buﬀer (ﬁanite); (b) double buﬀer (ﬁanite on porous GaAs). Advances in OptoElectronics 13 as Zr(Ce)O canbeusedas insulating layers (alternative N843 GaN/ZrO /por(mono)Si/Si 2 2 Raster 300 ∗ 300 mkm to SiO , SiC, and Si N ) in the development of Si-, 2 3 4 Ge- and GaAs-based “semiconductor-dielectric” multilayer structures. Fianite is also a good gate dielectric for Si- as III V well as for A B -based devices (including GaN-based) due to its high dielectric constant value (25–29.7). Thin ﬁanite ﬁlms are a barrier for diﬀusion of impurities and provide a signiﬁcant (up to 1000-fold and even more) decrease of the loss current in highly integrated devices [11, 12]. Due to high chemical inertness ﬁanite ﬁlms can also be used as protective coatings. 0 200 400 600 800 1000 1200 Sputtering time (s) 3.2. Techniques for Deposition of Fianite Films on Si and Si mono GaAs Substrates. In recent years, a considerable attention Si por was drawn to ﬁanite ﬁlms on silicon due to its electric (a) and optic device applications, such as insulating layers in GaN/ZrO /porGaAs/GaAs SOI (silicon-on-insulator) devices [29], gate dielectric in Si- III V Raster 200 ∗ 200 mkm 2stage/ [28, 29], SiGe- [30], and A B -based [31]devicestructures, Raster 400 ∗ 400 mkm 1stage/GaN GaN-substrate GaAs buﬀer layers for production of optic coatings for ﬁlms of various semiconductors [30–33], superconductors [34–36], 4 4 10 10 ferroelectrics. Various techniques can be used for the production of 3 3 10 10 ﬁanite ﬁlms on silicon and other semiconductors, including magnetron [36–40], laser and electron-beam [41–43]sput- 2 2 tering, and molecular-beam epitaxy (MBE), as well as gas- 10 10 phasechemicaldeposition[44]. 1 1 The choice of a speciﬁc technique is determined by 10 10 0 400 800 1200 1600 2000 0 200 400 600 800 further designation of a ﬁanite ﬁlm and possibility to Sputtering time (s) Sputtering time (s) produce the ﬁlm of maximum structural perfection, as well as technologic potentialities of the technique. So, MBE Ga2 Ga2 technique is more suitable for the deposition of the thinnest N N As As ﬁanite ﬁlm for the use as a gate dielectric. Magnetron and laser sputtering are more favorable for ﬁanite layers used (b) as buﬀer layers with subsequent growing semiconductor III V Figure 13: Results from a layer-by-lyer SIMS analysis of GaN/ ﬁlms, including A B compounds. In [36], ﬁanite ﬁlms ﬁanite/por(mono)Si/Si (a) and GaN/ﬁanite/porGaAs/GaAs (b) were deposited on Si and GaAs substrates using magnetron, structures. laser, and electron-beam sputtering techniques. The ﬁlms obtained by magnetron sputtering were of the best structural perfection [36]. 388 nm 3.3. Growing of Fianite Films on Si and GaAs Substrates. The growth of ﬁanite ﬁlms on silicon and gallium arsenide substrates was carried out with the purpose to evaluate the prospects of using less expensive and more large Si and 20000 GaAs substrates with ﬁanite sublayer instead of monolithic ﬁanite substrates because, currently, maximum size of the latter is ∼50 mm. Another purpose was the determination of an opportunity to use ﬁanite not only as a substrate but also as insulating layer material alternative to SiO , SiC, and Si N protecting and insulating layers, as well as 3 4 a gate dielectric for multi-layer “semiconductor-dielectric” 350 400 450 500 structures. Producing such substrates will allow integrating (nm) GaN-based optoelectronics with a well-developed silicon and gallium arsenide electronics and optoelectronics. Magnetron Figure 14: Photoluminescence spectra of GaN ﬁlms (300 K) on and laser sputtering were used for deposition of ﬁanite ﬁlms GaAs substrate with buﬀer layers: porous GaAs (1) and double buﬀer-ﬁanite on porous GaAs (2). on silicon and gallium arsenide Intensity (cps) Intensity (cps) Intensity (cps) 14 Advances in OptoElectronics 3.4. Fianite Films on Porous Si and GaAs. With the purpose (i) optic refractive index n ∼ 2.1 ÷ 2.2; to improve quality of ﬁanite ﬁlms and its adhesion to Si and (ii) dielectric constant ε ∼ 25; GaAs substrates, opportunities of the use of porous layers of (iii) absence of defects of porosity type (in 30 mm diame- the material were studied. ter sample). The following results were obtained: (i) appropriate regimes of deposition of porous GaAs layer on GaAs (111) substrates of n-and p-conduc- 3.6. Laser Sputtering Technique. Experimental installation for deposition of ﬁanite ﬁlms was a sputtering system tivity types were developed; composed by a vacuum device and excimer laser. The system (ii) appropriate regimes of deposition of the uniform has been designed and manufactured in IPM RAS. mirror-ﬂat ﬁanite layer on GaAs (111) substrates of Operational oxygen pressure was maintained by vacuum 18 × 18 mm size were established; system supplied with a mechanical pump and CHA-2 letting (iii) it has been demonstrated that the use of the porous system. Evaporation of the target was performed by LPX200 layers allowed an improvement of adhesion of ﬁanite eximer laser radiation working on KrF mixture. Wavelength with GaAs layers; of the radiation was 248 nm, pulse duration 27 ns, the pulse energy 350 MJ (pulse power 1.3 × 10 W), and repetition (iv) the samples of ﬁanite/GaAs and ﬁanite/Si epitaxial frequency 50 Hz. Optical system providing a focusing of substrates have been obtained for subsequent growth III the laser beam on the target surface consisted of quartz of A N ﬁlms. prisms and 30 cm focal distance lens. The laser beam spot High mechanical and chemical stability of ﬁanite and on the target surface was 1 × 4mm . The energy density absence of pores open the prospects of its application as on the target surface was ∼10 J/cm . The distance between protective and stabilizing coating for various substrates. the target and substrate was 60 mm. Cylindrical targets of 15–20 mm diameter and 10–30 mm length were used in the installation. In order to prevent local overheating of 3.5. Magnetron Sputtering Technique. Magnetron systems are the target and to provide a uniform material drift rotation related to diode-type sputtering systems. The sputtering an axial movement of the target was used. Possibility of occurred due to bombardment of a target surface by gas conducting pre- and postgrowth annealing under oxygen ions (usually Ar) forming in plasma of anomalous glow atmosphere at 10 Pa–100 kPa pressure and at up to 750 C discharge. Material ions knocked out the target subjected temperature is a peculiarity of the installation. to the bombardment are captured by the magnetic ﬁeld Ceramic target of (ZrO ) (Y O ) with x = 0.1 2 1−x 2 3 x and maintained complex cycloidal movement by closed composition was used for deposition of ﬁanite ﬁlms. The trajectory in vicinity of the target surface. High sputtering deposition was carried out on Si and GaAs substrates heated rate, which is a feature of magnetron systems, is achieved to 600–800 C temperature under oxygen atmosphere at by an increase of the ion current density due to localization approximately 10 Pa. The growth rate of YSZ ﬁlms was about of plasma by means of high transverse magnetic ﬁeld. The 0.02 nm per pulse. Contactless heater of substrates (heating increase of sputtering at simultaneous decrease of actuation by irradiance) was an original peculiarity of the sputtering gas pressure allows a signiﬁcant decrease of contamination system. The heater comprises vertically positioned quartz of the ﬁlms by alien gas impurities. Fianite was grown up on tube (of 30 mm inner diameter) supplied with refractory Si and GaAs substrates using unbalanced magnetron system. stainless steel heating coil on its outer surface with up to Fianite crystals were used as a target. Si substrate subjected to 1 kW power of the heater. Monitoring and maintenance of the sputtering was heated by IR radiance. Preparation of the the assigned temperature (with ±5 C precision) were carried substrates included degreasing, removing of the oxide, and out using precise regulating device and Pt-Rh thermocouple passivating of the surface in ammonium-peroxide solution. positioned under the heating coil. A substrate was ﬁtted in Optimization of the conditions of the growth of ﬁanite ﬁlms a holder and positioned inside of the quartz tube. Loading on Si substrates was carried out by varying of the sputtering of substrates and oxygen supply was maintained through the rate, temperature of the substrate, and residual gas pressure. upper end of the tube. Bombardment of the target leads to dissociation of zirconium and yttrium oxides to ZrO, Zr, YO, Y, and O . Technology of growth of dielectric ﬁanite ﬁlms using the That is why such parameters as sputtering rate and residual laser sputtering consists of the following stages. gas pressure considerably inﬂuence stoichiometry of the (1) A substrate is loaded to the sputtering system and the resulting ﬁlm. Energy of the evaporating particles is rather vacuum chamber is evacuated up to ∼1Pa residual low (∼0.5–10 eV); so for the epitaxial growth of ﬁanite ﬁlm, pressure. a high temperature of Si substrate and optimal rate of the condensate supply are necessary. (2) Letting-to-oxygen is maintained up to the pressure The ﬁanite ﬁlms were studied by means of scanning required. electron microscopy, ellipsometry, and CV-parameters mea- surement techniques. The ﬁlm parameters were found as (3) Rotational movement drive of the target is switched follows: on. Advances in OptoElectronics 15 (4) A substrate is heated up to deposition temperature. usually used at ﬁanite growth. As it has been shown by calculations, ﬁanite should not react with silicon substrate to (5) The eximer laser (the pulse energy 350 MJ, repetition form SiO , which has low dielectric constant value, at a direct frequency 50 Hz) is switched on and the sputtering is contact [45]. However, in practice, it is very diﬃcult to avoid started. the formation of this ﬁlm at ﬁanite deposition or subsequent (6) Followed by the achievement of the assigned thick- high-thermal treatment [46, 47]. Therefore, a development ness of the ﬁlm, the laser is switched oﬀ. of special technological tools is necessary. One of the routes (7) Followed by the end of the ﬁlm growth, the chamber to solve the problem has been suggested by the authors [48]. Thin Zr or Y layer was deposited on Si substrate before is ﬁlled with oxygen up to the pressure required. ﬁanite deposition. The metals absorb oxygen from SiO layer (8) The structure is annealed. because free energy of both ﬁanite and Y O formation is 2 3 The substrate heater is switched oﬀ and the substrate is lower than of SiO one [49]. That leads to a decrease of the layer thickness. cooled to room temperature. Second, oxygen from ﬁanite layer readily diﬀuses to silicon substrate or reacts with silicon surface. Secondary 3.7. Initial Stages of Deposition and Structure of Fianite Buﬀer phases occurring as a result of the reaction disturb silicon Layers on Si and GaAs Substrates. The application of ﬁanite crystal lattice and hinder a perfect growth. Under these cir- as a buﬀer layer will present a solution route to another very III cumstances, ﬁanite layers on Si substrates are of amorphous important problem: epitaxy of A N compounds on Si and or polycrystalline structure. At the development of gate GaAs substrates having large dimensions, high quality, and dielectric technology, these issues are of peculiar importance low net cost. because thickness of the last layer is about some nanometers. Single-crystalline heteroepitaxial ﬁanite ﬁlms of 1000 A Therefore, the above data show that the problem of thickness were grown on silicon substrates of up to 50 mm 2 deposition of ﬁanite ﬁlms on Si substrates is of great interest. diameter in vacuum chamber at p ∼ 2·10 Pa pressure, The problem of improvement of quality of the layers seems to sputtering rate V ∼ 60 A/min, and substrate temperature ◦ be very urgent because of a number of principal diﬃculties T ∼ 800 C. occurring due to peculiarities of physical-chemical proper- The studies have shown that the ﬁlm became continuous ties of the materials resulting in reactions at the growth and as from 100 A thickness. subsequent thermal treatment stages. The synthesis of perfect X-ray structural studies of ZrO -Y O /Si structures 2 2 3 ﬁanite ﬁlms on Si requires a development of special methods have shown that the ﬁanite ﬁlm was single phased and to decrease the inﬂuence of amorphous SiO layer at the consisted of two layers with diﬀerent rocking curve val- substrate-layer interface. ◦ ◦ ues: 0.20 for the upper layer and 0.96 for the lower one. Epitaxial relation between the ﬁlm and the substrate 3.9. Characterization of Fianite Films. The ﬁlms were studied was (100)[100] Si//(100)[100]ZrO -Y O . The relation was 2 2 3 established using diﬀraction measurements under the fol- by means of scanning electron microscopy, ellipsometry, and CV-parameters measurement techniques. lowing regimes: Θ/2Θ scanning (simultaneous rotation of the detector and sample over goniometer axis) and Ψ- scanning (rotation of the plate in a proper plane at ﬁxed 3.9.1. Capacity-Voltage Characteristic Measurements of the detector position). The former regime was used to determine “Fianite-on-Silicon” Structures. The capacity-voltage (CV) orientation of the composition plane, the latter-mutual characteristics of the structures supplied with ﬁanite ﬁlms orientation of unit cells of the ﬁlm, and the substrate in the deposited on p-Si and n-Si substrates were measured. composition plane. Capacity measurements provide evaluation of dielectric Spectra of the Ψ-scanning of (ZrO -Y O )/Si structure 2 2 3 properties of ﬁlms under the study: dielectric constant ε for asymmetric (422) reﬂection of the ﬁlm (b) and the and dielectric loss tgδ. The application of a multifrequency substrate (a) are shown in Figure 15. device allows the determination of frequency dependencies The absence of additional peaks and high peak maxi- of dielectric constant and high-frequency loss in dielectric mum-to-background ratio (∼10 ) are the evidence for ZrO - ﬁlms. Since the dielectric ﬁlm is deposited on a semicon- Y O layer is a perfect single-crystal ﬁlm. The ﬁanite buﬀer 2 3 ductor, a MIS structure (metal-insulator-semiconductor) is III layers grownonSiand GaAs were used forA N compounds formed, so the CV-measurement provides additional infor- epitaxy. mation concerning the semiconductor and the dielectric- semiconductor interface, namely, type of the semiconductor 3.8. Some Diﬃculties in Deposition of Fianite Films on Silicon conductivity (n or p) and concentration of the dopant, ﬂat Substrate. Growth of ﬁanite-on-silicon structures of high band barrier voltage V , density of boundary states, and a fb quality featuring with sharp interfaces is associated with charge induced in the dielectric. signiﬁcant diﬃculties because of a number of principal The device used for CV-measurements allowed deter- problems. mining the capacity and high-frequency conductivity of First, silicon surface readily undergoes transformation the structures, as well as its dependency on the applied into SiO amorphous layer either due to interaction with voltage. The measurements were carried out at 500 KHz and oxygen-containing ﬁanite ﬁlm or oxidative atmosphere 1 MHz frequencies. Direct potential bias range was ±40 V. 16 Advances in OptoElectronics 100 100 0 45 90 135 180 225 270 315 360 0 45 90 135 180 225 270 315 360 ◦ ◦ Ψ ( ) Ψ ( ) i i (a) (b) Figure 15: Ψ scanning spectra for (422) reﬂection of YSZ substrate (a) and the ﬁlm (b). Thermally sputtered Al of 1 mm surface diameter was used as the contacts. The results obtained are shown in Figure 16. “Al-ﬁanite-Si” MIS structure parameters: ﬂat band bar- rier voltage –4 V for 180 nm ﬁlm and 1.5 V for 20 nm ﬁlm; 12 −2 density of the boundary state charge ∼+10 cm . 3.9.2. Investigation of ZrO Films on Si and Ge Substrates by Means of Scanning Electron Microscopy. The ZrO ﬁlms were studied using scanning electron microscopy. All of the ﬁlms studied were porous-free. Since the square of the samples −10 −8 −6 −4 −20 2 4 6 8 10 studied was 5-6 cm , it is possible to consider the porosity −2 Potential bias (V) value at least not exceeding 0.15–0.2 cm . For comparison, −2 it is worth to mention that porosity of SiO ﬁlms is 4–8 cm . Figure 16: CV-characteristics of ﬁanite-on-p-Si sample. Therefore, it is possible to consider ZrO ﬁlms as a protective layer for Ge devices actually superior SiO ﬁlms because its porosity decreased in 1.5–2 orders of magnitude. that formation of larger elements of the relief occurred The study of morphology of the ﬁlms deposited by by enlargement of such particles. The reasons of local magnetron sputtering technique at high magniﬁcation has enlargement (formation of spherical hills) can be gradients shown its satisfactory homogeneity. Some regions of the of temperatureand mass transfer,aswellasoccurrenceof surface featured by a relief composed by quasi-spherical hills impurities. The observations allowed reﬁning the conditions of 500–600 nm in diameter and exhibiting lateral periodicity. of the sputtering of ZrO andﬁaniteﬁlmsinorder to Analytical study of the ﬁlms has shown an absence of minimize surface roughness. inclusions of impurities. An attempt to study the mechanism of formation of the ﬁlms with the purpose to optimize the conditions of 3.10. Fianite as a Gate Dielectric. Recently, a sharp surge of interest in the use of ﬁanite as a gate dielectric in CMOS magnetron sputtering was done using electron microscopy (JSM JEOL 5910 LV). The particles were identiﬁed by means technology has been observed. It is associated with an increase of leakage current at the use of conventional SiO of electron probe. The ﬁlm was removed by polishing using 2 by increasing the integration level. That requires a change of diamond paste with 2.5–4 μm particle size. This abrasive SiO over dielectrics with higher dielectric constant (high-k size was chosen to minimize decreasing particle size of the 2 materials) [30, 32, 33, 45]. The resent studies have limited ﬁlm constituents at the polishing. The obtained material possible alternatives to ﬁanite, HfO ,ZrO , and its silicates. was ﬂushed by ethanol (9–12 purity grade “for microelec- 2 2 For example, ZrO has high dielectric constant value, good tronics”) and the suspension was put in plastic syringes (1 mL). In order to disintegrate aggregates, ultrasonic (US) dielectric properties (5.8 eV energy gap width), and rather good crystallochemical matching with Si [50] (see Table 2). treatment was carried out. The US dispersion was conducted using “Sapphire 3 M-1.3” US device with 35 GHz operational Intel Corp., one of the leaders of the world electronics, has demonstrated that the change of SiO over HfO as a gate frequency. The syringes were inserted to the device chamber 2 2 ﬁlled with water. The chamber was thermostated at 27 C. dielectric in 45 nm technological process allows decreasing leakage currents, (which became a serious problem for Followed by 3 min of the US treatment, the suspension transistors) by more than two orders of magnitude [51]. was aspirated onto conductive (graphitized) ribbon for subsequent microscopy study. The study has shown that Comparison of ﬁanite ﬁlms [33]and SiO with electrical the largest constituents of the zirconia ﬁlm were quasi- equivalent oxide thickness of about 1.46 nm, has shown that spherical particles of 50–100 nm size that explained X-ray the leakage current for ﬁanite was four orders of magnitude amorphous nature of the ﬁlm. It is possible to suggest lower than that of conventional SiO gate oxides. Ncp 10 s Ncp 10 s Capacity (pF) Advances in OptoElectronics 17 Table 3: Parameters of growth and annealing of the ﬁanite-on-Si ﬁlms. Sample T of growth, C Annealing, 600 C, 10 min Film thickness, nm Substrate z1 Room Without annealing ∼20 Si B z2 Room Vacuum ∼20 Si B z3 Room Oxygen ∼20 Si B z4 Room Oxygen ∼20 Si Sb z5 600 Oxygen ∼20 Si B Table 4: Optimal modes of ﬁanite and ZrO sputtering. The hysteresis and interface state density in this ﬁlm was 2 11 −1 −2 measured to be less than 10 mV and 2.0 × 10 eV cm . Target material Fianite ZrO Thus, such crystalline oxide on semiconductor could be used Installation Z-400 Z-550 for future generation of semiconductor-based devices. Target diameter ∅ 70 mm ∅ 203 mm It is worth to note that quality of the synthesized ﬁanite, −3 −3 Argon pressure 5 ∗ 10 mBar 5 ∗ 10 mBar as well of the interfaces, is very important for integration of Power ∼500 Wt ∼400 Wt such a dielectric to the CMOS technology currently in use. ˚ ˚ Synthesizing of ﬁanite-on-silicon structures of high Film growth rate 100 A/min ∼50 A/min quality featuring with sharp interfaces is associated with signiﬁcant diﬃculties described above. One of the routes to solve this problem is in application magnetron power, plasma is unstable (“blinking plasma”); of low-temperature growth and annealing regimes, as those, in case of larger values of discharge power, the growth rate which were used in the series of experiments described below, increases, but irregularity of the surface patterns and growing type of a substrate, and the annealing media were also varied. ﬁlm coarse-graining were observed on a number of samples. Conditions of the synthesis of the ﬁanite/Si structures are Fianite sputtering requires higher power than in case of given in Table 3. XRD technique has shown that ﬁanite layers ZrO , at the same time the growth rate was twice as much obtained by laser deposition at room temperature were of thanincaseofZrO . amorphous structure. The developed technique of magnetron sputtering made Subsequent postgrowth recrystallization annealing it possible to vary the ﬁanite ﬁlm thickness between 600 resulted in arising of a polycrystalline phase in the ﬁlm. At and 2000 A. The optimization of the sputtering modes the same time, the layers sustained mirror ﬂat and uniform. allowed producing of Ge and Si plates with ﬁanite ﬁlms Proﬁle of the surface of z4 sample (Table 4) obtained using of satisfactory quality. Ge plates with ﬁanite ﬁlms were Talysurf interference microscope is shown in Figure 17(a). used to try out further operations of the device structures Roughness of this ZrO surface was estimated as Sq = production: photolithography and etching. 0.852 nm that does not practically diﬀer from roughness of the Si substrate used for the ﬁanite growth (Sq = 0.7877 nm). 3.12. Protective and Stabilizing Properties of Fianite Films Preliminary studies of gate properties of thin (10– on Ge. Inorganic dielectric coatings are usually used for 15 nm) ﬁanite ﬁlms obtained by laser deposition on Si passivating and protection of p-n transition surface, as substrates have been carried out. The studies conducted on shielding and thermal compensation layers at ion implanting the test structures with deposited Al contacts have shown and for interference antireﬂecting protection. Passivation of that thin ﬁanite ﬁlms featured with low values of loss the surface is the most important issue for manufacturing −12 2 currents, minimum values being 10 A/cm at 1 V voltage of germanium photodiodes because natural GeO and GeO (Figure 17(b), samples z3 and z4). oxides are unstable and, so, cannot be considered as the only passivating coatings. It is one feature distinguishing Ge and Si devices (the latter have stable and rather eﬃcient 3.11. Fianite and ZrO as Protective and Stabilizing Layers on coating formed by its own SiO oxide). This oxide ﬁlm Ge and Si Substrates and Multilayer Structures deposited from a gas phase is of the most frequent use 3.11.1. Deposition Modes. Fianite and zirconium dioxide for photodiodes, with p -n-structure. It has positive charge and by attracting electrons to the surface prevents growth ﬁlms were deposited by magnetron sputtering technique, 2 types of vacuum evaporation Leybold Heraeus units of p-channels thus decreasing probability of generation in the layer. It is worth to note that for improved reliability (Z-400 and Z-550) with diﬀerent target dimensions were used: 70 mm in diameter for ﬁanite and 203 mm—for ZrO and stability of characteristics of photodiodes, it is necessary 11 −2 −1 (Table 4). to maintain surface state density at 10 cm eV level. However, this passivating technique is far from ideal because High-frequency and direct voltage modes of sputtering of the high porosity of SiO ﬁlms that decreases humidity were tested. By using the latter mode it was impossible to 2 resistance and reliability of the device. provide suﬃcient ﬁlm growth rate, so HF sputtering mode (13.56 MHz) was chosen. The optimal modes of ﬁanite and In order to improve dielectric properties of the protective ZrO sputtering are also shown in Table 4.Incaseoflow coating, ﬁanite ﬁlms deposited by magnetron sputtering were 2 18 Advances in OptoElectronics −1 Z2 −2 Z5 −3 −4 −5 Z1 −6 −7 −8 Length = 101 μm; Pt = 3.995 nm; scale= 10 nm −9 Z3 Z4 4 −10 −11 −12 −2 −4 −13 0 10 20 30 40 50 60 70 80 90 100 01 2 3 (μm) V (A) (a) (b) Figure 17: Surface roughness of ﬁanite ﬁlm on Si substrate, sample z4 (a); and leakage current of Al/ﬁanite/Si structure (b) samples z1–z5 were prepared under diﬀerent conditions. used. The opportunity of its application for maintaining high-quality practically porous-free protective coating has been conﬁrmed earlier by the experiments. It has been demonstrated that the use of ﬁanite protective layer in Ge-structures instead of SiO eliminated pulse noise and thus considerably improved photoelectric and performance characteristics of these devices. It has been established that the improvement was related to a more uniform nature of ﬁanite ﬁlms, in particular, absence of pores, in comparison with SiO ﬁlms, which contain defects 10 in form of pores. 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 3.13. Some Properties of the Device Structures Supplied Wavelength λ (μm) with Zirconium Dioxide Films. Photoelectric characteristics Figure 18: The dependency of the reﬂection on wavelength of and noise of germanium photodiodes supplied with ZrO silicon sample coated with ZrO ﬁlm of 1200 A thickness. and SiO ﬁlms described above have been investigated. Monochromatic sensitivity of these photodiodes is typical for germanium devices and equals to 0.5-0.6 A/W (at 1.06 and using these ﬁlms have demonstrated the advantages of 1.55 μm wavelengths). The change SiO over ZrO resulted 2 2 zirconia-based solid solutions in application to photosensi- in somewhat decrease of a dark current (on average for 10%). tive apparatus technology. Main improvement of the photodiodes quality achieved due to the application of ZrO ﬁlms was revealed at the noise studies. Under the voltage exceeding operational one (that 3.14. Studies of Optical Properties of ZrO Films. Optical corresponds to accelerated reliability testing conditions), the refraction of ZrO equals to 1.98 ÷ 2.1, that is, close check samples with SiO ﬁlms have shown pulse noise of 2 to ﬁanite one; therefore this material is also promising telegraphic type in the oscillogram, which can be associated for antireﬂection coatings. Determination of the refraction with processes of energizing-deenergizing of the surface constant n and monitoring of the ﬁlm thickness d were conducting channels [51]. The defects occurring because of carried out using ellipsometry technique. The experimentally the presence of pores in SiO ﬁlms are probable cause of 2 determined values of d depended on duration of the ﬁlms arising of the channels. In the batch with ZrO protective ˚ ˚ 2 growth and varied within 600 A–1100 Arange. ﬁlms, only shot noise, which is in principle unavoidable, The ﬁlms obtained have shown rather high refraction was observed. More detailed results of the device studies are constant ∼2 ÷ 2.1. These values were signiﬁcantly higher presented in [52]. than that of SiO (1.45). Thus, the studies performed on ﬁanite and zirconium In theory, considering an incident beam from air (vac- dioxide ﬁlms as well as on the device structures developed uum), it is possible to decrease the reﬂection to zero when (nm) I (A) Reﬂectance (%) Advances in OptoElectronics 19 0.32 0.4 0.3 0.38 0.36 0.28 0.34 0.26 0.32 0.24 0.3 0.22 0.28 0.2 0.26 0.18 0.24 0.16 0.22 0.2 0.14 0.18 0.12 0.16 0.1 0.14 0.08 0.12 0.06 0.1 0.04 0.08 0.02 0.06 0.04 0.02 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 λ (μm) 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 λ (μm) Ge Si (a) (b) Figure 19: Experimental (1) and theoretical (2) dependencies of the reﬂection on wavelength in Ge-ﬁanite antireﬂecting ﬁlm system (1300 A) (a); experimental dependencies of the reﬂection of ﬁanite ﬁlm on Si and Ge (b). the refraction constant of an antireﬂecting ﬁlm corresponds the corresponding thickness of a ﬁlm d) at n = n ,where d f to the following equation: n -optical refraction constant of a semiconductor. Since for Si and Ge the constants are equal to 3.7 and 4, respectively, n = n , (1) the reﬂection is completely eliminated at n = n ≈ 2. d f Therefore, a dielectric having its optical refraction constant where n -refraction constant of a semiconductor. In case of n = n ∼ 2(at n = 3.7 ÷ 4) canbeconsideredasan d f f Si and GaAs, n ∼ 3.5 ÷ 4, thus n ∼ 1.9 ÷ 2. Therefore, f f optimal material for the antireﬂecting ﬁlm for solar cells and ZrO ﬁlms obtained actually satisfy perfect antireﬂection 2 the other photosensitive devices. Theoretically, at the ﬁlm for Si and GaAs-based devices from the viewpoint of n. thickness, which is equal to a quarter of optical wavelength Moreover, the diﬀerence in n-values of SiO and ZrO ﬁlms 2 2 W = λ/4n , such dielectric allows a complete elimination of provides an opportunity for the antireﬂection over a broad the reﬂection loss (R = 0). spectral range due to application of binary SiO +ZrO 2 2 The refraction constant of SiO (n = 1.47) is consid- 2 d antireﬂecting coatings. The dependency of the reﬂection erably lower than that value. At this n value it is impossible constant on wavelength of silicon sample coated with ZrO to maintain the reﬂection loss lower than 10%. Refraction ﬁlm of 1200 A thickness is presented in Figure 18.Theoretical constants of ﬁanite and ZrO are within (2.15 ÷ 2.18) and absorption minimum corresponds to λ = 4n · d = 4 · 2.1 · (2.13 ÷ 2.2), respectively, that is close to the above optimum 0.12 ≈ 1 μm. value. Thus, providing an evidence that ﬁanite and ZrO are As it is apparent from Figure 18, the reﬂection minimum very promising as antireﬂecting coatings for solar cells and III V was approached at λ = 0.97 μm. Thus, the experimental min the other photosensitive devices based on Ge, Si, and A B results are in conformity with the theory practically com- compounds. plete. Experimental dependencies of antireﬂection (as depen- Therefore, ZrO ﬁlm ensures high antireﬂection quality: dencies of the reﬂection on wavelength) of ﬁanite ﬁlms on Si at λ , the reﬂection loss does not exceed 2-3%. The data min and Ge have been plotted (Figure 19). obtained conﬁrm that ZrO is an excellent material for The plots apparently demonstrate that the reﬂection antireﬂecting ﬁlms, as well as ﬁanite. drops to 0–1.5% in the minima. Experimental study of antireﬂective properties of ﬁan- ite oxide applied to Ge was performed. By the reason 4. Fianite as Antireﬂecting Layer for that germanium photodetectors are designed for detecting Solar Cells radiation generated by lasers with wavelengths λ = 1.06, 4.1. Antireﬂecting Properties of Fianite Film on Ge and Si. In 1.3, and 1.54 μm, thickness of the antireﬂective ﬁanite ﬁlm theory, it is possible to eliminate the reﬂection completely (at was chosen as W = 1300 A; such thickness provides for R, rel. units R, rel. units 20 Advances in OptoElectronics 0.12 0.12 0.11 0.11 0.1 0.1 0.09 0.09 0.08 0.08 0.07 0.07 0.06 0.06 0.05 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.01 0.01 0 0 0.4 0.5 0.6 0.7 0.8 0.9 1 0.4 0.5 0.6 0.7 0.8 0.9 1 1 3 2 4 (a) (b) (c) ˚ ˚ Figure 20: Antireﬂecting properties (reﬂection spectra) of ﬁanite ﬁlms of 580 A (a) and 1050 A (b) thickness. The experimental data were obtained on the industrial items s (c) of Si solar cells of “4 x 4” size. minimal reﬂection losses in the considered wavelength range As it is shown in Figure 19(a), in the range of funda- λ = 1.06–1.54 μm. Figure 19(a) shows the comparison of mental absorption (for λ< 1.65 μm), the experimental curve experimental (thin line) and theoretical (bold line) R(λ) 1 coincides with the theoretical curve 2. Some discrepancy curves. The theoretical R(λ) curve was calculated using the at higher wavelengths (λ> 1.65 μm) appears due to deep following formula: penetration of such radiation and its reﬂection from the back surface. It is important that at the optimal wavelength R =1 (λ = 1.12 μm), ﬁanite ﬁlm provides for ideal antireﬂective properties, the reﬂection is actually absent. In rather large n n (2) range 0.88–1.55 μm, into which radiation wavelengths of the − . 2 2 2 2 2 most wide spread lasers fall, the losses for reﬂection do not n n +1 − n −n n −1 sin (2πn W/λ) f d d f d d exceed 10%. According to the above formula, reﬂection may fall The experimental dependences of enlightenment (the practicallytozeroatthe optimalvalue of n (note that dependence of reﬂectance on the wavelength) of cubic in case of SiO antireﬂective ﬁlm, for which n = 1.47, 2 d zirconia ﬁlms on Si and Ge (Ge by its optical properties is it is impossible to obtain reﬂection lower than 10%). The similar to GaAs) exhibit excellent antireﬂective properties of minimal reﬂection is achieved at the following wavelength cubic zirconia (Figure 19(b)). As is evident from the graphs, λ : the minimum reﬂection can drop to 0-1, 5%. Position of the min minimum depends on the thickness of the ﬁlm. When it gets λ = 4Wn . min d (3) thinned twice, the minimum would be in the solar spectrum. Advances in OptoElectronics 21 Plateau in the curve shows the reﬂection from the back side [2] S. Yu. Kuz’minov, E. E. Lomonova, and V. V. Osiko, Cubic Zirconia and Skull Melting, Cambridge International Science, of the substrate in the transmission range for Si. So the gain UK, 2009. due to the use of the antireﬂecting ﬁanite ﬁlm reaches 20– [3] V. V. Osiko, M. A. Borik, and E. E. Lomonova, “Synthesis of 30%. refractory materials by skull melting technique,” in Handbook So, it was experimentally proved that for 1300 A thick of Crystal Growth, pp. 433–469, Springer, 2010. ﬁanite ﬁlm, reﬂection may actually drop to zero in the [4] I. Golecki, H. M. Manasevit, L. A. Moudy, J. J. Yang, and J. wavelength range λ = 1.06–1.54 μm. E. Mee, “Heteroepitaxial Si ﬁlms on yttria-stabilized, cubic A new, unusual application of ﬁanite as a reﬂecting zirconia substrates,” Applied Physics Letters, vol. 42, no. 6, pp. ﬁlm (in contrast to antireﬂecting!) was suggested. Such 501–503, 1983. unexpected use may appear useful for screening of peripheral [5] D. Pribat, L. M. Mercandalli, J. Siejka, and J. Perriere, (nonphotosensitive) photodetector areas. Various routes of “Interface oxidation of epitaxial silicon deposits on (100) formation of photosensitive areas or metallic masks sput- yttria stabilized cubic zirconia,” Journal of Applied Physics, vol. 58, no. 1, pp. 313–320, 1985. teredonSiO are currently in use for the screening. But [6] L. M. Mercandalli, D. Diemegand, M. Crose, and Y. Sierka, such solution causes notable spurious capacitance of the “Recent progress in epitaxial growth of semiconducting metal-oxide-semiconductor structure; provided that such materials on stabilized zirconia single crystals,” Proceedings capacities are inadmissible in a number of photodetectors, of the Society of Photo-Optical Instrumentation Engineers, vol. in particular, in high frequency photodetectors. In case 623, pp. 133–210, 1986. of screening by the reﬂecting oxide (for this purpose, the [7] G. Shengurov, V. N. Shabunov, A. N. Buzynin et al., “Silicon thickness should be chosen as W = 1/2λn ), no surface heterostructures on ﬁanite substrates,” Microelectronics, vol. 6, capacity is being formed, because spurious capacitance is p. 204, 1996. absent. In such case, ﬁanite ﬁlm may reﬂect about 60% of [8] A. N. Buzynin, V. V. Osiko, E. E. Lomonova, N. Yu. Buzynin, radiance from the surface. and A. S. Usikov, “Epitaxial ﬁlms of GaAs and GaN on ﬁanite substrate,” in Proceedings of the Materials Research Society Symposium, vol. 512 of Wide-Bandgap Semiconductors for High 4.2. Silicon Solar Cells with Fianite Antireﬂecting Layers. Power, High Frequency and High Temperature, pp. 205–210, Experimental dependencies of antireﬂection of ﬁanite ﬁlms Pittsburg, Pa, USA, 1998. depositedoncommercialsolar cellswererecorded. The [9] A. N. Buzynin, V. V. Osiko, K. Yu. Voronko et al., “Epitaxial reﬂection spectra of ﬁanite obtained on two such samples GaN and GaN As ﬁlms on monolithic and porous GaAs x 1−x are shown in Figure 20. The plots (Figures 20(a) and substrates with ﬁanit sublayer,” Bulletin of the Russian Academy 20(b)) demonstrate excellent antireﬂecting properties of the of Sciences: Physics, vol. 69, no. 4, pp. 557–562, 2005. ﬁanite ﬁlms. The plots also apparently demonstrate that the [10] P. A. Anderson, C. E. Kendrick, R. J. Kinsey et al., “(111) and (100) YSZ as substrates for indium nitride growth,” Physica reﬂection drops to 0–1.5% in the minima. A position of Status Solidi C, vol. 2, no. 7, pp. 2320–2323, 2005. the minimum depends on the ﬁlm thickness. At the ﬁlm [11] S. J. Wang, C. K. Ong, S. Y. Xu et al., “Electrical properties of thinning the minimum occurs in solar spectrum. Therefore, crystalline YSZ ﬁlms on silicon as alternative gate dielectrics,” energy gain due to the application of the antireﬂecting ﬁanite Semiconductor Science and Technology, vol. 16, no. 3, pp. L13– ﬁlms approaches to 20–30%. L16, 2001. [12] S. J. Wang and C. K. Ong, “Rapid thermal annealing eﬀect 5. Conclusions on crystalline yttria-stabilized zirconia gate dielectrics,” Semi- conductor Science and Technology, vol. 18, no. 2, pp. 154–157, Due to the unique combination of physical and chemi- 2003. cal properties, ﬁanite is a very promising multifunctional [13] A. N. Buzynin, V. V. Osiko, E. E. Lomonova et al., “Epitaxial material for novel electronic technologies. Experimental ﬁlms of III-V compound on ﬁanite substrates,” in Proceedings of the International Congress on Advanced Materials, Their data and some theoretical considerations presented in the Processes and Applications, article 672, pp. 25–28, Munich, review demonstrate prospects of the material application Germany, September 2000. either as monolithic dielectric substrate or buﬀer layer for [14] P. D. C. King,T.D.Veal,S.A.Hatﬁeld et al., “X-ray heteroepitaxy of semiconductor structures and as a material photoemission spectroscopy determination of the InN/yttria for insulating, antireﬂecting, and protective layers for various stabilized cubic-zirconia valence band oﬀset,” Applied Physics device structures, as well as a gate dielectric. Considering Letters, vol. 91, no. 11, Article ID 112103, 3 pages, 2007. the performance characteristics, ﬁanite (cubic zirconia) was [15] T. Nakamura, Y. Tokumoto, R. Katayama, T. Yamamoto, and shown to be in advance in comparison with the other K. 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Publisher: Hindawi Publishing Corporation
Copyright: Copyright © 2012 Alexander N. Buzynin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Abstract

Hindawi Publishing Corporation Advances in OptoElectronics Volume 2012, Article ID 907560, 23 pages doi:10.1155/2012/907560 Review Article 1 2 1 Alexander N. Buzynin, Yury N. Buzynin, and Vitaly A. Panov A. M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow 119991, Russia Institute for Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod 603950, Russia Correspondence should be addressed to Alexander N. Buzynin, abuzynin@yandex.ru Received 7 January 2012; Accepted 2 May 2012 Academic Editor: Jung Huang Copyright © 2012 Alexander N. Buzynin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Fianite or yttrium stabilized zirconia (YSZ) solid solutions single crystals were known worldwide as jewelry material. The review is devoted to novel applications of the material in the ﬁeld of microelectronics. A number of modern aspects of the application of ﬁanite in micro-, opto- and SHF-electronics were analyzed in this paper. It was demonstrated that ﬁanite is an extremely promising multipurpose material for new electronic technologies due to unique combination of physical and chemical properties. III V As a substrate and buﬀer layer for the epitaxy of Si, Ge, GeSi and A B compounds (GaAs, InGaAs, GaSb, InAs, GaN, AlN), ﬁanite has a number of advantages over the other dielectric materials. The use of ﬁanite (as well as ZrO and HfO oxides) instead of SiO 2 2 2 as gate dielectrics in CMOC technology seems to be of peculiar interest. The unique properties of ﬁanite as protecting, stabilizing and antireﬂecting coatings in electronics and optoelectronic devices have been outlined. A comparative study of the performance characteristics of ﬁanite and conventional materials has been carried out. 1. Introduction A number of application prospects of ﬁanite in modern electronics are considered in this paper. The further progress in electronics is connected with appli- cation of new materials. Fianite is a material of such a kind. 2. Fianite as a Substrate and Buffer Layer for Industrial technology of synthesis of ﬁanite has been for Epitaxy of Semiconductors, Multilayer the ﬁrst time developed in Russia in the Lebedev Physical Heterostructures, and Superlattices Institute of the Russian Academy of Sciences (FIAN in Russian), so the crystals were entitled after the Institute [1]. Appropriate conditions of growth of mirror-ﬂat single- Serial production of the crystals has been already started IV III V crystalline ﬁlms of A :Ge, GeSi,and A B compounds: in the early seventies of the twentieth century. Currently, GaAs, InGaAs, GaSb, InAs, GaN, AlN, and InN as well ﬁanite crystals are in the second position by the volume as multilayer InGaAlAs heterostructures and GaSb/InAs of worldwide production following silicon [2, 3]. Fianite supperlattices on ﬁanite substrates, as well as on Si and single crystals, -zirconia-based solid solutions (or “yttrium GaAs substrates coated with ﬁanite buﬀer layer, using stabilized zirconia” YSZ), were known as jewelry stone MOCVD, HW-CVD, and laser deposition techniques have imitation materials. Recently, in the countries with the been elaborated. All of these ﬁlms have been for the ﬁrst time developed microelectronics a signiﬁcant growth of interest synthesized in Russia. to various aspects of ﬁanite application in semiconductor technologies has been observed. Fianite is an extremely promising multipurpose material for new optoelectronics 2.1. FianiteasaSubstrateand Buﬀer Layer for Si, Si- III V technologies due to its unique combination of physical and Ge, and A B Compounds Epitaxy. Fianite has a number chemical properties. It can be used in, virtually, all of the of advantages as a substrate and buﬀer layer at Si and III V main technological stages of the production of electronic A B compounds epitaxy, as compared with other dielectric devices (Figure 1). materials [4–13]. 2 Advances in OptoElectronics TheﬁrstepitaxialSiﬁlmsonYSZ were grownin[6]. Fianite ZrO (HfO )−Y O The ﬁrst successful results on epitaxial MOCVD growth of 2 2 2 3 III V various A B compounds (GaAs, InAs, InGaAs, AlGaAs, GaAsN, and GaN) on YSZ are presented in a number of Epitaxy of semiconductors studies [6, 11, 12], InN on YSZ in [14, 15]. In [13, 16] Functional f ]ilms a capillary epitaxy technique—the new eﬀective way of heteroepitaxy was developed. It has been shown that the Gate dielectric Substrate Insulating Protective use of capillary forces in the method positively inﬂuences and buﬀer layer both on the mechanism of epitaxial growth and on quality Antireﬂexion of A B epitaxial ﬁlms and also reduces the minimum III V thickness of a continuous layer [16, 17]. Figure 1: Application of ﬁanite in electronics. An application of ﬁanite as either monolithic substrate or buﬀer layer in “semiconductor-on-dielectric” technology is of peculiar importance for micro- and optoelectronics. In comparison with the other dielectrics, there are the The technology allows improving such characteristics of following merits of ﬁanite in application as a substrate integrated circuits as operation speed, critical operational III V material and buﬀer layer for Si and A B compounds temperature, and radiation resistance. epitaxy: Due to a decrease of the loss of current and stray (i) High resistivity—> 10 Ohm·cm at 300 K. capacitance, energy consumption of the devices is decreas- III V ing. Moreover, the devices based on “semiconductor-on- (ii) Similarly to Si, Ge, and A B compounds, it is dielectric” structures are more reliable, especially under of cubic structure (in contrast to hexagonal of extreme operational conditions. Currently, “silicon-on- sapphire). insulator” structures are one of the most dynamically devel- (iii) It is possible to alter ﬁanite cubic lattice constant oping directions in the ﬁeld of semiconductor materials sci- in solid solutions by varying the ratio of the main ence. However, electrophysical and operational parameters (zirconium or hafnium dioxide) and stabilizing of the devices as well as its radiation resistance and reliability oxides (yttria, rare earth oxides from gadolinium signiﬁcantly suﬀer because of structure imperfection of to lutetium, and alkaline-earth oxides) that allows silicon layers. In case of “silicon-on-sapphire” structures, the an optimum matching between substrate and cubic imperfection is determined, in particular, by a diﬀerence in lattice of semiconductor ﬁlms thus improving its crystallographic structure of silicon and sapphire, as well as structural perfection. by autodoping of a silicon ﬁlm by aluminum penetrating (iv) Negligible value of diﬀusion coeﬃcients of cations from the sapphire substrate in concentrations up to 10 – 20 −3 up to 1000–1200 C temperature range that excludes 10 cm . Considering crystal-chemical and physical char- interdiﬀusion of impurities between the substrate acteristics of ﬁanite, the material is more preferential for the and ﬁlm and prevents undesirable doping (i.e., typ- epitaxy of Si as an alternative substrate in comparison with ical for sapphire), which can damage heteroepitaxial sapphire. layers through penetration of impurity atoms. (v) Due to its excellent stability at elevated temperatures, 2.2. Silicon-on-Fianite Epitaxial Structures. The ﬁrst stud- the upper limit of the corresponding structure oper- ies on silicon epitaxy on ﬁanite single-crystal substrates ational temperatures depends on physical properties have been carried out in France and USA [6, 7]. Silicon of a semiconductor only. Elevated temperature is not ﬁlms on ﬁanite substrate were deposited by chloride and critical for the substrate. hydride epitaxy at 900–1100 C. The ﬁlms obtained were (vi) Broad spectral range of transmission (260–7500 nm) of polycrystalline structure and, consequently, of rather completely covers actual absorbance and emission poor electrophysical parameters. However, at the same time, III V of Si, A B compounds and its solid solutions. it was shown that silicon-on-ﬁanite structures sustaining That makes “semiconductor-on-ﬁanite” structures actually all advantages of silicon-on-sapphire are free from very promising for the development of various its principal drawbacks. optoelectronic devices with improved operational At the epitaxy of Si on ﬁanite, a formation of SiO parameters (avalanche photodiodes, light-emitting intermediate layer between the ﬁlm and the substrate was and laser diodes, etc.). observed [7, 8]. Subsequent annealing of the structure led (vii) Application of thin layers of ﬁanite on Si and GaAs to the increase of SiO layer thickness. It was demonstrated instead of its monolithic substrates allows avoiding [8] that the layer can improve properties of silicon-on-ﬁanite spatial limitations of the structures and decreasing epitaxial structure because its formation: the net cost. At the same time, the structures on “ﬁanite/Si” and “ﬁanite/GaAs” episubstrates have better heat conductivity in comparison with the (i) removes mechanical stress in the layer-substrate structures on monolithic substrates. interface; Advances in OptoElectronics 3 (ii) smoothens over negative eﬀect occurring due to a mounted on the cooled current leads. There was a Ta plate of diﬀerence of linear expansion coeﬃcients between 80 × 5 × 0.5 mm size installed in one of the sources position. ﬁanite and silicon; Before the epitaxial growth, the sources and substrates were subjected to 10 min annealing at 1350 and 1250 C, (iii) improves insulation of the integrated circuit elements respectively, then temperature of the source was increased (ICE) based on Si; to 1380 C, as the substrate temperature was decreased to (iv) acts as a barrier for metal impurities diﬀusing from assigned values (600–700 C) and the buﬀer layer was grown. the substrate and forming deep levels in silicon. The pressure in the cell corresponded to basic one. In order to grow Ge layers, the cell was ﬁlled with GeH The formation of SiO intermediate layer at high- −3 −6 up to 1·10 –5·10 torr and the pressure was maintained temperature epitaxy is associated with peculiar properties of constant by a system of the gas feeding. Simultaneously, ﬁanite. In contrast to the other dielectrics, ﬁanite features the Ta plate situated in vicinity of the substrate was heated with a unique peculiarity as a solid electrolyte: starting to T = 1200 C. With the purpose to avoid destruction from 650 C, it becomes actually oxygen-transparent due to of germane on evaporators (Ti) following preepitaxial high mobility of oxygen. The reason for signiﬁcant mobility annealing of the sources and substrates, the sublimating of oxygen in ﬁanite crystals is an occurrence of oxygen pumps were switched oﬀ and the growth was carried out +4 +3 vacancies due to Zr to Y cation substitution at formation at pumping down using only diﬀusion- and booster-pumps. of the solid solution. High mobility of oxygen in ﬁanite It is worth to note that the gas ﬁlling up to such high crystals is determined by an occurrence of oxygen vacancies −3 pressure (∼10 torr) is impossible in MBE installations with at ZrO (HfO )–R O (here: R-Y, Gd–Yb) solid solutions 2 2 2 3 electron-beam heating. Germane pressure in the cell was +4 +4 +3 formation due to Zr (Hf )toR cation substitution. The tentatively assigned by ionization vacuum gage indications. process results in oxygen nonstoichiometric ZrO (HfO ) 2 2 Nevertheless, this peculiarity in GeH pressure measurement based phase [4]. Because of the high mobility of oxygen did not impede the controlled growth of Ge ﬁlms at at high temperature of the epitaxy (900–1000 C) used in 700–750 C temperature of the substrate. The ﬁlms were [6–8], the formation of ether SiO continuous layer or its continuous and homogeneous. GeSi solid solutions with islets between the substrate and the ﬁlm was shown to be up to 80% Si content were also obtained on (111) and inevitable. (100) ﬁanite substrates. Vacuum annealing at 1250 C during The phenomenon occurs even at the epitaxy initial stages 10 min was used as a preepitaxy treatment. The growth when a continuous epitaxial ﬁlm is forming. It was shown [9] −4 was carried out under 5·10 torr germanepressureand at that the formation of SiO layer or isles at the initial stage of 600 C substrate temperature. Simultaneously, the Ta plate molecular-beam epitaxy on ﬁanite results in 3-dimensional positioned in vicinity of the substrate was heated to 1200 C. mechanism of growth, formation of structural defects and The heteroepitaxial Ge ﬁlms obtained show high structural hindered the synthesis of Si ﬁlms of single-crystal structure. perfection. X-ray rocking curve (XRC) FWHM values were The occurrence of the isles at the initial epitaxy stages and 0.31 for Ge ﬁlm. The surface morphology of the Ge epitaxial the polycentric growth of Si layers were shown possible to layers grown on (100) and (111) ﬁanite substrates as well as avoid only by using a set of techniques, those which prevent −1 the peaks of Raman scattering near 300 cm are identical to diﬀusion of oxygen from the substrate to the ﬁlm at the those of bulk Ge. Therefore, it is possible to conclude that initial stage of the process. In particular, high structural there are no stains in the Ge/ﬁanite layer. perfection of the Si-on-ﬁanite ﬁlms was achieved by using a low-temperature (T< 650 C) molecular-beam epitaxy [7]. III V 2.4. Epitaxial Films of A B on Fianite. Crystallochemical and physical properties of ﬁanite are favorable not only for 2.3. Ge and GeSi Films on Fianite Substrates. Growth of III V silicon but also for A B compounds epitaxy (Table 1). Ge and Ge-Si heterostructures on ﬁanite substrates was III V carried out using HWCVD installation. Base pressure in the First successful results on growth of A B compound −8 chamber ∼1·10 torr was maintained by pumping-down epitaxial ﬁlms on ﬁanite substrates were presented in [10, III V using two heteroionic pumps. A high-vacuum gate was used 18]. GaAs, InAs, GaN, and other A B semiconductor for isolation of the growth cell and the pumps from other compound ﬁlms have been grown on ﬁanite, as well as parts of the vacuum system. Forepumping of the chamber on silicon and gallium arsenide with ﬁanite buﬀer layer was performed using a diﬀusion pump. The diﬀusion pump substrates by means of metal-organic chemical vapor deposi- allowed to exhaust any gas (including GeH )bothinatomic tion (MOCVD). A new eﬃcient epitaxy technique-“capillary and molecular state. FM-1 oil with low vapor pressure was epitaxy” has been suggested. The technique allowed synthe- III V used as a pressure ﬂuid. There was a nitrogen trap above sizing of A B compound ﬁlms by a MOCVD on ﬁanite the diﬀusion pump preventing reverse diﬀusion of the oil substrates. Samples of structurally perfect submicron (up III V from preevacuation and diﬀusion pumps into the growth to 0.1 μ) epitaxial ﬁlms of A B compounds have been cell. The (100) and (111) oriented ﬁanite single-crystal plates obtained using this technique. The samples demonstrated were used as substrates. Silicon atomic beam was maintained high electrophysical parameters [13, 17–20]. In [21], GaN by sublimation of the element single-crystal (high resistance) epitaxial ﬁlms have been grown on ﬁanite substrates by in form of 4 × 4 × 90 mm ingot sections. The sources were MOVP technique. It was observed that the epitaxial growth 4 Advances in OptoElectronics III V Table 1: Some properties of ﬁanite crystals and A B compounds. Lattice −6 −1 T , C (melting point) Crystal Thermal expansion coeﬃcients 10 deg E ,eV Type a, A 5.141 (x = 10) (ZrO ) (Y O ) Cubic (ﬂuorite) 2800 11.4 (15–1000 C) 2 2 3 5.157 (x = 15) 100−x x 5.198 (x = 21) GaAs Cubic (sphalerite) 5.65 1283 5.4 1.43 GaP Cubic (sphalerite) 5.445 1467 4.7 2.26 a = 3.186; GaN Hexagonal (wurtzite) 1700 5.6; 7.8 3.4 c = 5.178 GaN Cubic (sphalerite) 4.52 1700 3.9 3.2 a = 3.54 InN Hexagonal (wurtzite) 1200 12.7 0.7 c = 5.70 InN Cubic (sphalerite) 1200 4.4 0.67 4.98 of GaN on ﬁanite signiﬁcantly depends on conditions of the leading to growth according to the Volmer-Weber mecha- initial stage of the process. nism. Formation of the continuous layer occurred through 3-dimensional nuclei, their subsequent growth and joining. In [11, 22, 23], ﬁanite substrates were successfully tested Low nuclei density results in the formation of highly inho- for growth of InN heteroepitaxial ﬁlms. InN ﬁlms of cubic mogeneous rough surface that hinders subsequent formation structure have been grown on (001) ﬁanite substrates by of a ﬂat ﬁlm. A laser sputtering technique is considered to plasma-stimulated molecular-beam epitaxy (RF-MBE) at maintain high nuclei density; so, before joining, the nuclei 400–490 C temperature. The lattice mismatch of InN and are of suﬃciently small size that promotes the formation of a ﬁanite at (001) plane is very low (less than 2.3%), in contrast ﬂat continuous ﬁlm. to 17% for InN sapphire and more than 10% for InN-GaAs. Due to this fact, InN ﬁlms grown on (001) ﬁanite substrate Therefore, in order to obtain ﬂat layers, a laser sputtering were superior InN ﬁlms grown on sapphire [10] and (001) technique was used in the study. GaAs substrates by its crystallographic perfection [15]. The Q-switched Nd laser and single-crystal GaAs and Therefore, ﬁanite is apparently in advance as a substrate InAs targets were used. The superlattices were grown by for InN epitaxy as compared to sapphire. A new eﬀective optical switching of the laser beam between the targets. method of heteroepitaxy, capillary epitaxy, was proposed Mirror-ﬂat GaSb and GaAs:Sb layers as well as penta- in [17]. In particular, this technique allows us to obtain periodic InAs/GaSb supperlattices of 0.15 μm total thickness III V the ﬁlms of A B compounds on ﬁanite using a MOCVD were deposited using this technique. approach. The X-ray diﬀraction investigations of GaAs:Sb (111) ﬁlms on ﬁanite (111) showed their single-crystal structure (Figure 2(a)). It was shown that the spectral dependence 2.4.1. Deposition of GaAs, GaSb, GaAs:Sb Films, and GaSb/ of photoconductivity of GaSb ﬁlms on ﬁanite substrates InA Superlattice on Fianite Substrates by Means of Laser (Figure 2(b)) has a maximum of photoconductivity at the Sputtering. Our experiments have shown that the conven- edge of fundamental absorption. This eﬀect may be due to tional “direct” growth of heteroepitaxial InGaAs ﬁlms on high velocity of the surface recombination. ﬁanite substrates resulted in the ﬁlms with rough surface. The X-ray rocking curve (XRC) FWHM value was 0.23 So the buﬀer layers were elaborated to improve the results. The buﬀer layer must have very high structural perfection for GaSb (111) ﬁlm. The image of the surface of GaAs:Sb (0.2 μm thickness) on ﬁanite is shown in Figure 3(a).Itisappar- and mirror-homogeneous surface. A number of experiments ent that the surface of the layer is mirror ﬂat and suﬃciently were conducted for growth of GaAs, GaSb, and GaAs buﬀer layers on ﬁanite (100) and (111) substrates as well homogeneous. The microrelief of the layer surface is shown in Figure 3(b). According to our estimations, roughness of as GaSb/InAs superlattice by using laser sputtering. This superlattice is working as a ﬁlter, which prevents penetration the layer is less than 4 nm (Sq = 0.003778 μm). of the defects into InGaAs ﬁlm and, ﬁrst of all, formation of In the penta-periodic InAs/GaSb supperlattices of growing dislocation. Furthermore, Sb is an eﬀective surfac- 0.15 μm total thickness grown on (111) ﬁanite substrates tant which signiﬁcantly improves the ﬁlms morphology. electron mobility approaches to 580 cm /V × s. The GaSb The studies have shown that it was complicated to obtain layers, as well as InAs/GaSb short-period supperlattices, are III V thin and homogeneous layers of A B compounds on ﬁanite suitable for the development of IR detectors operating in substrates. It may be related to rather high mismatching a2-3 μm range. In our studies, the structures were used as III V III of the lattice parameters of ﬁanite and A B compounds buﬀers for A N growth on ﬁanite substrates. Y : 99.2 μm Advances in OptoElectronics 5 Measurement of GaSb photoconductivity, 2.5 Si–ﬁlter XRD–spectra Z5551S Z5551S 1.5 0.5 1.2 1.3 1.4 1.5 1.6 1.7 1.8 24.5 25 25.5 26 26.5 2θ (deg) λ (mkm) (a) (b) Figure 2: XRD θ/2θ scan of GaSb (111) ﬁlm on ﬁanite (111) (a) and photoconductivity of GaSb ﬁlm on the ﬁanite substrate (b). 3D surface 606.52 Length = 69.81 μm; Pt = 6.064 nm; scale= 10 nm −2 −4 Azimuth: 66.3 (deg); elevation: 40.7 (deg) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 X scale: 1; Y scale: 1; Z scale: 1 (μm) (a) (b) Figure 3: Image of surface (a) and the surface relief (b) of GaAs:Sb buﬀer on ﬁanite. 2.4.2. MOCVD Capillary Epitaxy of III-V Compounds on growth stages showed that the transition from conventional Fianite. The investigations showed that continuous GaAs MOCVD growth to capillary epitaxy leads to a change in the ﬁlms on ﬁanite can be obtained only in a very narrow growth mechanism. Three-dimensional island mechanism range of the epitaxial conditions. In particular, a temperature changes to the two-dimensional one with propagation of range of 550–600 C is necessary. The minimum thickness the growth steps (Figure 4(a)). This process is similar to of a continuous layer was 1.5–2.0 μm. The epitaxial ﬁlms graphoepitaxy [24, 25] from aqueous solutions with addition had polycrystalline structure and rough surface. Structural of surfactants, where an increase in the substrate wettability and electrical properties of GaAs ﬁlms could be improved also signiﬁcantly improves the quality of graphoepitaxial using capillary epitaxy. The essence of this method is that layers [24](Figure 4(b)). a thin (less than 50 nm) ﬁlm of an III-group element is In both cases, the height of the crystallization medium initially deposited on ﬁanite surface and then saturated (melt or solution) decreases in the initial stage due to the with a V-group component with the formation of a thin capillary forces. This eﬀect impedes growth of epitaxial continuous epitaxial III-V layer. Following this procedure, nuclei in the direction normal to the substrate surface the ﬁlm growth continues to obtain the necessary thickness and facilitates their growth in the tangential direction. under conventional epitaxial conditions. As a result, the substrate orienting role increases and a The use of capillary forces in the ﬁrst (heteroepitaxial) transition to the layer-by-layer growth mechanism occurs stage of GaAs ﬁlm formation led to improvement of epitaxial with a decrease in the growth step height. Consequently, the quality. Electron microscopy of the GaAs ﬁlms at the initial minimum height of the continuous ﬁlm decreases and the :98.41 μm S (a.u.) (nm) (nm) 6 Advances in OptoElectronics (a) (b) Figure 4: Analogy between the capillary epitaxy and graphoepitaxy. (a) Electron microscopy image of GaAs on YSZ at the initial stage of growth (20000x): conventional MOCVD, height of the islets is up to 3000 nm. (b) The capillary epitaxy technique, minimal layer thickness is 50 nm, the layer growth is visible [18]. Optical microscopy image of NH J on amorphous Al graphoepitaxy growth: without (c) and with (d) the use of surface-active substances, magniﬁcation 100x [24]. ﬁlm structural quality is improved. It has been shown that Mobility Transistor) for microwave frequency FET operating the use of capillary forces in this technique improved both in 10–40 GHz range (Table 2) using “Aixtron AIX 200RF” III V the mechanism of epitaxial growth and quality of A B installation. Capillary epitaxy MOCVD technique in 550– epitaxial ﬁlms. It also reduces the minimum thickness of 600 C temperature range was used. acontinuouslayer [14, 18]. Virtually the same approach Grown by the “capillary epitaxy” technique series of III to deposition of A N ﬁlms on various substrates has been GaSb and GaAs:Sb buﬀer layers on (111) and (100) ﬁanite successfully applied in studies of the other authors [26]. substrates were developed to decrease surface roughness The use of capillary epitaxy made it possible to decrease of the PHEMT heterostructure. The buﬀer layers had a minimum thickness of a continuous GaAs/ﬁanite ﬁlm to uniform mirror-smooth surface of about 5 nm roughness. 25 nm and to improve its structural quality and surface Application of the developed buﬀers made it possible morphology. The technique was also eﬃcient for growing of to obtain an AlGaAs/InGaAs/GaAs heterostructures with III V the other A B compounds on ﬁanite. uniform mirror-smooth surface on ﬁanite substrates and to decrease its roughness by a factor of 10 (to 25 nm). 2.4.3. Deposition of GaAs, AlGaAs, and InGaAs-Based Multi- As a result, suﬃciently homogeneous AlGaAs/InGaAs/GaAs layer Structures on Fianite. The results on epitaxial growth multilayer heterostructures with smooth slightly bloom III V of A B compound ﬁlms obtained in the studies described surface were grown on (001) ﬁanite substrates of 50 mm above were used for obtaining of AlGaAs/InGaAs/GaAs diameter. Roughness of the heterostructure surface mea- multilayer heterostructures on ﬁanite. These structures were sured using Talysurf interference microscope (3-dimensional III V used in FET. Sequential growth A B heteroepitaxial lay- topography) was 0.25 μm. This structure was grown using ers on ﬁanite substrates was conducted according to the “AIXTRON” installation on (100) ﬁanite ellipsoidal substrate topologic scheme of PHEMT (Pseudomorphic High Electron of 2 inch major diameter. The surface of the multilayer Advances in OptoElectronics 7 Table 2: PHEMT heterostructure for FET operating in 10–40 GHz crystallochemical parameters and high chemical stability. range. Besides ﬁanite, Si and GaAs substrates with ﬁanite buﬀer layer were developed in scope of the work. Synthesis of the + 18 −3 n GaAs:Si n ∼ 6 × 10 cm 40 nm Si layer was carried out by a laser deposition technique. The i-Al Ga As x ∼ 0.24 (>0.23) 25 nm x 1−x growth of ﬁanite ﬁlms on silicon substrates was conducted i-GaAs ∼0.6 nm with the purpose to evaluate prospects of the use of less −2 δ-Si n ∼ 4.5 × 10 cm Si expensive large silicon substrates with ﬁanite sublayer instead i-GaAs ∼0.6 nm of monolithic ﬁanite because maximum dimensions of the i-Al Ga As x ∼ 0.24 4 nm silicon-on-ﬁanite structures are limited by size and quality of x 1−x i-GaAs 1 nm ﬁanite crystals and the corresponding substrates (currently ∼50 mm). i-In Ga As y ∼ 0.18 (<0.2) 11 nm y 1−y Another purpose of the study was determination of i-GaAs 30 nm suitability of ﬁanite not only as a substrate material but i-Al Ga As x ∼ 0.24 50 nm x 1−x 14 also as a gate dielectric. Production of such substrates −3 i-GaAs n< 8 × 10 cm 0.5–0.8 μm will allow integrating GaN-based optoelectronics with a CP AlAs/GaAs (1nm/2nm) × 5 well-developed silicon and gallium arsenide electronics and GaAs:Sb 100 nm optoelectronics. Fianite substrate 400 μm GaN Films on Fianite Substrates. Growth of the ﬁlms on (111) and (100) oriented ﬁanite substrates was carried out structure is rather uniform but its roughness reaches the using nucleus layers. 3 types of the nucleus layers were used: value of 25 nm. Structural perfection of AlGaAs/InGaAs/GaAs multi- (1) low-temperature GaN nucleus layer with annealing layer heterostructures on ﬁanite was investigated by means in hydrogen-ammonia atmosphere; of XRD. DRON-4 device (Ge(004) monochromator, CuKα1 (2) low-temperature AlN nucleus layer with annealing in radiation) was used. Θ/2Θ spectra were recorded at sym- hydrogen-ammonia atmosphere; metric reﬂection mode by scanning with 0.1 step of the (3) high-temperature AlN nucleus layer. texture maxima rocking. X-ray diﬀraction Θ/2Θ spectrum of GaAs (001)/ﬁanite (001) is shown in Figure 5. The peaks of At the use of all of the types of the nucleus layers, ﬁanite (Zr,Y)O (004), 2θ = 73.4 substrate and of GaAs (004), 2θ = ◦ substrates were annealed in pure hydrogen at ∼1070 C 66.05 buﬀer layer were recorded. The width of the layer before deposition of the ﬁlms. rocking curve FWHM = 1, that is, the evidence of a mosaic ◦ Hydrogen is a conventional carrier gas in MOGPE of structure of GaAs layer. The grain-boundary angle was ∼1 . III-V materials because it can be rather readily puriﬁed. The use of (111) ﬁanite substrates with GaAs:Sb buﬀer layers Similarly, in MOGPE of nitrides of III group hydrogen for for deposition of AlGaAs/InGaAs/GaAs heterostructures on the ﬁrst time was used as a carrier gas. However, later it was ﬁanite resulted in the formation of mirror-ﬂat homogeneous demonstrated that in contrast to classic III-V semiconduc- surface and 10-fold decrease of the surface roughness (up to tors, GaN and InN are unstable under hydrogen atmosphere 0.025 μm). and undergo destruction (etching) at the temperatures used Detailed data on elemental and molecular composi- for growth of these crystals. This is an evidence for hydrogen tions of the heterostructures were obtained by means of as a carrier gas at the epitaxy of nitrides of III group elements layer-by-layer SIMS (“TOF SIMS-5” spectrometer). The actively participates in the process occurring on the surface sputtering was carried out by Cs , 2 keV, raster 250 × of the growing ﬁlm, in contrast to GaAs. Therefore, in 250 μm, negative ion detection mode, the probe beam Bi , most cases for growth of nitrides of III group by MOGPE, 25 keV, and depth resolution DZ > 7 nm. The analysis ammonia is used as a nitrogen source and supplied into of the AlGaAs/InGaAs/GaAs heterostructures obtained on reactor in large quantities. For a long time, ammonium was ﬁanite (Figure 5(b)) has shown that its inner topology was of opinion that it inhibits the destruction of a growing ﬁlm in conformity with the assigned scheme (Table 2) of the and makes the eﬀect of hydrogen negligible. However, it PHEMT structure. appears that it is far from the case and hydrogen signiﬁcantly inﬂuences the process of the nitrides growth. III 2.4.4. A N Films on Fianite Substrates and Buﬀer Layers. The studies have shown that at annealing of LT-GaN Principal diﬃculty of growth of perfect heteroepitaxial GaN nucleus layer, the latter undergo etching in H -NH ﬂow 2 3 ﬁlms is an absence of suitable substrates having good match- hindering growth of a high-quality GaN ﬁlms. Application ing with the heteroepitaxial ﬁlm. Currently, for the growth of of the low-temperature AlN nucleus layer with annealing GaN ﬁlms, Al O , ZnO, MgO, SiC, Si, and GaAs substrates in hydrogen-ammonia atmosphere as well as the high- 2 3 are in use. Usually, a material with wurtzite structure is temperature AlN nucleus layer on (111) and (100) oriented grown on a hexagonal substrate, whereas sphalerite is grown ﬁanite substrates resulted in formation of hexagonal GaN on a cubic one. Fianite as a substrate material for cubic ﬁlms comprising a textured polycrystal of hexagonal mod- InGaN epitaxy has a number of advantages, such as favorite iﬁcation. Scattering angles of the texture for the GaN ﬁlms 8 Advances in OptoElectronics n GaAs: Si AlAs/GaAs InGaAs AlGaAs GaAs: Sb YSZ XRD–spectrum i-GaAs AB7A % (C) % (O) % (As) ### % (AlAs) % (SiAs) % (Zr) % (GaAs) % (SbAs) % (InGaAs) 66 67 68 69 70 71 72 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2θ (deg) Depth (mkm) (a) (b) Figure 5: XRD θ/2θ scan (a) and layer-by-layer secondary ion mass-spectrometry (b) of AlGaAs/InGaAs/GaAs (001)/ﬁanite (001) multilayer heterostructure. grown on the (111) and (100) oriented substrates were 10 XRD–spectra H1058B/YSZ111 and 15 ,respectively. H1058B YSZ100 It has been shown that high-temperature annealing of LT-GaN buﬀer layer at 1000–1100 C promotes improvement of structural perfection GaN heteroepitaxial ﬁlms. The GaN layers on ﬁanite substrates exhibited an intense photolumi- nescence with maximum at 365 nm. The conditions of growth of single-crystal GaN ﬁlms on (111) and (100) ﬁanite substrates by MOCVD without buﬀer layer at 850 C substrate temperature have been determined. The spectra of θ/2θ scanning were obtained using Ge (400) monochromator (Figure 6). Two peaks of the substrate were observed at 30 YSZ 29 30 31 32 33 34 35 36 37 (111) and 34.8 YSZ (200). The ﬁlm provides a single GaN 2θ (deg) (0002) peak at 34.5 . Since GaN (0002) peak is close to Figure 6: XRD θ/2θ scan of GaN ﬁlms on (111) and (100) ﬁanite YSZ (200) one, a narrow slit in front of the detector was substrates. inserted with the purpose to increase the resolution. GaN hex (0001) was detected on both substrates at FWHM of the XRC < 1 that corresponds to the epitaxial growth. Traces of temperature. Before the deposition of AlN ﬁlms, ﬁanite the polycrystalline phase at 32.4 (expected 0.1–1.0 intensity substrates were annealed in pure hydrogen at ∼1070 C. units) were not detected. Mirror-ﬂat homogeneous AlN ﬁlms with the roughness not exceeding 0.6 nm (Figure 7) were deposited on (100) and AlN Films on Fianite Substrates. The AlN ﬁlms on ﬁanite (111) ﬁanite substrates. substrates were grown using an MOGPE technique. The Layer-by-layer analysis of AlN nucleating layer on the Al Ga N direct gap semiconductors are very useful in the x 1−x ﬁanite substrates was carried out by SIMS using TOF SIMS-5 development of UV photodetectors. By altering Al content device (sputtering by Cs+, 2 keV, 250 × 250 raster, negative in GaN-based solid solutions, it is possible to obtain the recording mode, Bi+ probe beam 25 keV). material with a forbidden band ranging 3.43–6.2 eV thus The study has shown that the ﬁlms had uniform distribu- covering 200–365 nm spectral band. This spectral band tion of its constituents, the concentration proﬁle of Zr atoms is of practical importance in UV astronomy, ozone layer at the heterointerface being very sharp (Figure 7(c)). The use monitoring, combustion, and water sensors. These ﬁlms are of AlN nucleating layers on the ﬁanite buﬀering layers allows both of original interest as well as are useful as nucleating and deposition of continuous and homogeneous GaN ﬁlms of buﬀer layers in GaN epitaxy. hexagonal modiﬁcation. Growth of the ﬁlms was started from thin 20–50 nm nucleating layer. Two growth modes were used: at 650 C with subsequent annealing in ammonia-hydrogen media at Deposition of InN Single-Crystal Films on YSZ Substrates by 1100 C during 30 min followed by growing up of the basic Means of LP-MOCVD Technique Using Pulse-Capillary Epi- layer and high-temperature growth of AlN at the same taxy. InN heteroepitaxial ﬁlms attract a signiﬁcant interest Intensity (cps) Advances in OptoElectronics 9 Length = 101 μm; Pt 2.825 nm; scale= 5nm −0.5 5.854 nm −1.5 −2.5 101 μm 101 μm −3.5 −4.5 0 1020 30 40 50 6070 80 90 100 (μm) (a) (b) H1005B1 Cs 2 keV AlN/ZrO 0 100 200 300 400 500 Sputtering time (s) C 3 O Zr Al ZrO AlN (c) Figure 7: Image of surface (a) and the surface relief (b) (Interference Microscope “Talysurf ”); results obtained by layer-by-layer SIMS analysis (c) of the low temperature AlN layer on ﬁanite substrate (TOF SIMS-5). because the ﬁlms provide an opportunity of the development In [5], InN epitaxial ﬁlms have been for the ﬁrst of high-frequency electronic devices. Since an industrial time deposited on ﬁanite substrates by pulse-capillary LP- technology of InN substrates production is so far absent, MOCVD. The technique was shown to allow a signiﬁcant improvement of the ﬁlms quality, as well as synthesizing heteroepitaxial growth of InN on foreign substrates is single-crystal InN ﬁlms of hexagonal modiﬁcation. The required. Al O and Si substrates, being well developed and 2 3 ﬁlms demonstrated rather perfect morphology along with having considerable dimensions along with excellent crystal high photoluminescent and electrophysical characteristics. perfection, seem to be of the most interest. Moreover, Si is The structures on ﬁanite substrates were grown under low not expensive and allows a combination of the InN-based pressure in vertical reactor supplied with rotating molyb- devices with well-developed silicon electronics. However, denum stand (designed in IPM RAS). The substrates were mismatching between Al O , Si, and InN lattice constants is 2 3 inductively heated, trimethyl indium (TMIn) and ammonia rather large, 25% and 8%, respectively. That was the reason were the element sources, and nitrogen was the carrier why ﬁanite (YSZ) has been recently taken into account as an gas. The substrates of (111) and (100) orientations were alternative substrate. used. Comparative studies of the InN ﬁlms were carried For the ﬁrst time ﬁanite substrates have been successfully out using optical and electron microscopy, SIMS, XRD, tested for deposition of InN heteroepitaxial ﬁlms in [4]. photoluminescence, and probe techniques. The ﬁlms of cubic symmetry were grown on (001) ﬁanite The experiments on deposition of InN ﬁlms on ﬁanite substrates using plasma-assisted molecular beam epitaxy by MOCVD technique have shown that it was diﬃcult to (PA-MBE) at 400–490 C. grow a uniform and smooth InN ﬁlm using general growth Due to better crystal-chemical matching between InN process, as well as single-step capillary epitaxy, because of and ﬁanite, the ﬁlms grown on ﬁanite substrates exhibited three-dimensional nucleation. Satisfactory results have been crystal perfection better than those grown on sapphire and achieved only by using pulse-capillary epitaxy, in which the GaAs substrates [4]. process of intermittent supply of In (in form TMIn) at Intensity (cps) (nm) 10 Advances in OptoElectronics (a) (b) Figure 8: Morphology of the surface of InN ﬁlms deposited by means of conventional (a) and pulse-capillary LP-MOCVD techniques (b) (scanning electron microscope Supra 50 VP). constant NH ﬂow was repeatable [7]. The pulse-capillary XRD–spectrum LP-MOCVD deposition was started by puﬃng TMIn in H1142A nitrogen without ammonia inﬂow during 20 s followed by 40 s interruption of TMIn supply and puﬃng nitrogen- ammonia mixture. TMIn ﬂow was equal to 0.25 sccm/min. The procedure was repeated ten times and then the growth of InN ﬁlm was conducted at 550 CinN -TMIn-NH gas 2 3 5 6 mixture. The V/III reactant ratio was in the range of 10 –10 . Under these conditions growth of InN ﬁlms of 0.3 μ thickness was observed. The application of “pulse-capillary epitaxy” technique and ﬁanite substrates resulted in the formation of mirror-ﬂat ﬁlms of single-crystal structure. The comparative studies on growth (nucleation and formation of the primary 30 31 32 33 2θ (deg) continuous layer) of InN ﬁlms on ﬁanite substrates by means of LP-MOCVD and conventional MOGPE techniques have Figure 9: XRD θ/2θ scan of the InN ﬁlm. demonstrated signiﬁcant diﬀerences in size, habitus, and concentration of the epitaxial nuclei, as well as in mor- phology of the epitaxial layers. Raster electron microscopy and LP-MOCVD using pulse-capillary epitaxy are 1.0 (Supra 50 VP) images of the surface of InN layers deposited and 0.19 (curves 2and 1on Figure 10), respectively. It by means of conventional LP-MOCVD (a) and pulse- is noticeable that the latter value is considerably lower. capillary LP-MOCVD techniques (b) are shown in Figure 8. Therefore, the growth on ﬁanite results in more structurally Roughness of the surface of InN layer of 0.3 μ thickness perfect InN ﬁlms due to better crystallographic matching, grown by the conventional technique is apparently seen. other conditions being equal. Herewith, application of the The roughness occurred because of the three-dimensional pulse-capillary epitaxy allows achieving of record values that nucleation. is the evidence of excellent perfection of InN ﬁlms obtained At the same time, pulse-capillary epitaxy resulted in more in this study. smooth and uniform surface. θ/2θ scanning spectrum of InN The nondoped epitaxial InN ﬁlms grown on ﬁanite sub- ﬁlm deposited on (111) ﬁanite substrate by pulse-capillary 19 3 strates were semiconductors of n-typewith2.5 ∗ 10 cm LP-MOCVD technique and rocking curves of InN ﬁlms are electron concentration. It is also noticeable that Hall mobility presented in Figure 9. The 2θ peaks in the spectrum are value approaches 320 cm /V × s. The ﬁlms showed intense attributed to 30.0—YSZ (111) substrate, 31.3—InN (0002) photoluminescence with peak maximum at 0.87 eV. layer, and 33.0—In (100). The rocking curve of InN (0002) ﬁlm deposited on YSZ substrate by means of pulse-capillary epitaxy is shown in 2.4.5. Electrically Active Defects in GaN Films on GaAs Figure 10. Rocking curves of InN ﬁlms deposited on YSZ Substrates with Fianite Buﬀer Layers. Comparative studies and sapphire substrates by means of conventional techniques of density and electric activity of structural defects in are shown for comparison. The rocking curve data of InN GaN epitaxial ﬁlms grown on GaAs substrates with various (0002) peak provide full width at half maximum 1,8 for buﬀer layers were carried out by an induced bias technique the ﬁlms grownonsapphire(curve3on Figure 10). The (IBT). The technique has been developed rather recently values obtained for ﬁanite ﬁlms grown using conventional [27, 28]. It is a contact-free similarity of the induced current Advances in OptoElectronics 11 optoelectronics. However, there are three considerable prob- lems occurring at GaN epitaxy: ﬁrst, a signiﬁcant parameter mismatch of GaN layer and Si or GaAs substrates; second, the diﬀerence of thermal expansion coeﬃcients of the layer and the substrates and third, insuﬃcient chemical and thermal stability of the substrates at the epitaxial temperature. Application of various buﬀer layers, in particular, ﬁanite- based, canbeaneﬃcient method for solution of the above problems. GaN epitaxial ﬁlms were grown by MOCVD tech- nique using capillary epitaxy on Si and GaAs substrates with various buﬀer layers. Trimethylgallium (TMG), arsine (AsH ), and ammonia (NH )wereusedasGa, As,and N 3 3 8 10 12 14 16 18 20 sources, respectively. Single (ﬁanite, layer of porous Si, or ω (deg) GaAs material) and double (ﬁanite on porous Si and GaAs) were tested. The ﬁrst “prominent” porous buﬀer layer was suggested to allow decreasing thermoelastic strains in the second heteroepitaxial buﬀer thus improving its morphology Figure 10: Rocking curves of (0002) InN. and structure. The upper buﬀer layer, being chemically stable in the growth medium, provides ﬁne matching with functional heteroepitaxial ﬁlm. The epitaxial structures were studied using a set of technique (EBIC-mode). IBT is a nondestructive contact- techniques: photoluminescence (PL), scanning electron free method for diagnostics of semiconducting materials and microscopy in electron-beam induced current (EBIC-mode), microelectronic devices. IBT is based on detecting voltage (or and secondary-ion mass spectroscopy (SIMS). charge) generated by an electron probe of scanning electron It was established that the use of ﬁanite buﬀer layer microscope (SEM). Draft scheme of the method is shown in on Si substrate prevents formation of amorphous silicon Figure 11(a). nitride. The GaN ﬁlms grown on Si substrates with ﬁanite The electron probe (e) scans the surface of a crystal buﬀer layer were of hexagonal modiﬁcation (α-GaN) and under the study (O). Metal ring (D), in which the surface had mosaic single-crystal structure. It was demonstrated that charge generated by electrons through capacitive coupling the use of porous Si in the complex ﬁanite/Si buﬀer allows is induced, is a detector of a signal. The signal from the improving the adhesion of GaN ﬁlm and its uniformity by ring electrode is monitored in the SEM display (or by other phase composition and thickness. measurement equipment) through charge-sensitive ampli- Layer-by-layer SIMS analysis of GaN ﬁlms grown on Si ﬁer (PA) (Figure 11(a)). The technique allows qualitative and GaAs substrates with ﬁanite buﬀer layers has shown monitoring of semiconductor plates, structures, and devices that ﬁanite layer serves as a barrier for diﬀusion of Si and identifying electric active inhomogeneities such as disloca- As into GaN ﬁlm from Si and GaAs substrates, respectively tions, stacking faults, microfractures, extent of doping by (Figure 13). Good insulating properties of ZrO in the various dopants, all p- n junctions, and Schottky barriers (see 2 double buﬀer provide an opportunity to use “Semiconductor e.g., Figures 11(b) and 11(c)). Quantitative measurements of on dielectric” technology, which is promising to improve the local fundamental characteristics of semiconductors are also integration level. possible (diﬀusion distance, nonequilibrium carrier lifetime, its surface recombination rate, diﬀusion barrier height). Comparative studies of PL spectra (recorded at 300 K) The studies have shown that the use of GaAs substrates of GaN ﬁlms grown on a monolithic GaAs substrate and with porous GaAs layer resulted in a decrease of the electric GaAs substrates with various kinds of buﬀer layers have been activity of structural defects in the GaN ﬁlms and in an carried out (Figure 14): 1 single buﬀer “porous GaAs;” 2 increase of its electrical uniformity as compared to GaN double buﬀer “ﬁaniteonporousGaAs.” ﬁlms grown on monolithic GaAs substrates. The use of The position of PL peaks in the spectra corresponds to GaAs substrates with double buﬀer layer (ﬁanite on porous characteristic peak of cubic GaN. Consequently, the use of GaAs) allows additionally decreasing concentration of the single buﬀer layerofporousGaAsaswellasdoublebuﬀer electrically active defects in GaN ﬁlms to more than an order layer (ﬁanite on porous GaAs) allows growing GaN ﬁlms of of magnitude (Figure 12). cubic modiﬁcation. The growth of GaN ﬁlm on monolithic GaAs substrate in contrast resulted to the formation of hexagonal modiﬁcation. 2.4.6. GaN Films on Si and GaAs Substrates with Fianite Buﬀer Layers. Silicon and gallium arsenide are promising III substrates for GaN and the other A N epitaxy due to 3. Functional Fianite Films their high quality, large dimensions, and a low net cost, as well as possibility to integrate GaN-based devices with 3.1. Functional Fianite Films on Si, Ge, and GaAs Substrates. well-developed silicon and gallium arsenide electronics and Thin ﬁlms of ﬁanite and related solid solutions such X-ray intensity (a.u.) 12 Advances in OptoElectronics PA (a) 20 kV x10000 1 μ 20 kV x10000 1 μ (b) (c) Figure 11: Outline of the induced potential technique (a) and scanning electron microscope images of electrically active polygonal defects in GaAs ﬁlms: secondary-electron emission mode (b); b-induced potential mode (c). 20 kV x1000 10 μ 20 kV x1000 10 μ (a) (b) Figure 12: Electrically active defects in GaN ﬁlm on GaAs substrate with buﬀer layers: (a) single buﬀer (ﬁanite); (b) double buﬀer (ﬁanite on porous GaAs). Advances in OptoElectronics 13 as Zr(Ce)O canbeusedas insulating layers (alternative N843 GaN/ZrO /por(mono)Si/Si 2 2 Raster 300 ∗ 300 mkm to SiO , SiC, and Si N ) in the development of Si-, 2 3 4 Ge- and GaAs-based “semiconductor-dielectric” multilayer structures. Fianite is also a good gate dielectric for Si- as III V well as for A B -based devices (including GaN-based) due to its high dielectric constant value (25–29.7). Thin ﬁanite ﬁlms are a barrier for diﬀusion of impurities and provide a signiﬁcant (up to 1000-fold and even more) decrease of the loss current in highly integrated devices [11, 12]. Due to high chemical inertness ﬁanite ﬁlms can also be used as protective coatings. 0 200 400 600 800 1000 1200 Sputtering time (s) 3.2. Techniques for Deposition of Fianite Films on Si and Si mono GaAs Substrates. In recent years, a considerable attention Si por was drawn to ﬁanite ﬁlms on silicon due to its electric (a) and optic device applications, such as insulating layers in GaN/ZrO /porGaAs/GaAs SOI (silicon-on-insulator) devices [29], gate dielectric in Si- III V Raster 200 ∗ 200 mkm 2stage/ [28, 29], SiGe- [30], and A B -based [31]devicestructures, Raster 400 ∗ 400 mkm 1stage/GaN GaN-substrate GaAs buﬀer layers for production of optic coatings for ﬁlms of various semiconductors [30–33], superconductors [34–36], 4 4 10 10 ferroelectrics. Various techniques can be used for the production of 3 3 10 10 ﬁanite ﬁlms on silicon and other semiconductors, including magnetron [36–40], laser and electron-beam [41–43]sput- 2 2 tering, and molecular-beam epitaxy (MBE), as well as gas- 10 10 phasechemicaldeposition[44]. 1 1 The choice of a speciﬁc technique is determined by 10 10 0 400 800 1200 1600 2000 0 200 400 600 800 further designation of a ﬁanite ﬁlm and possibility to Sputtering time (s) Sputtering time (s) produce the ﬁlm of maximum structural perfection, as well as technologic potentialities of the technique. So, MBE Ga2 Ga2 technique is more suitable for the deposition of the thinnest N N As As ﬁanite ﬁlm for the use as a gate dielectric. Magnetron and laser sputtering are more favorable for ﬁanite layers used (b) as buﬀer layers with subsequent growing semiconductor III V Figure 13: Results from a layer-by-lyer SIMS analysis of GaN/ ﬁlms, including A B compounds. In [36], ﬁanite ﬁlms ﬁanite/por(mono)Si/Si (a) and GaN/ﬁanite/porGaAs/GaAs (b) were deposited on Si and GaAs substrates using magnetron, structures. laser, and electron-beam sputtering techniques. The ﬁlms obtained by magnetron sputtering were of the best structural perfection [36]. 388 nm 3.3. Growing of Fianite Films on Si and GaAs Substrates. The growth of ﬁanite ﬁlms on silicon and gallium arsenide substrates was carried out with the purpose to evaluate the prospects of using less expensive and more large Si and 20000 GaAs substrates with ﬁanite sublayer instead of monolithic ﬁanite substrates because, currently, maximum size of the latter is ∼50 mm. Another purpose was the determination of an opportunity to use ﬁanite not only as a substrate but also as insulating layer material alternative to SiO , SiC, and Si N protecting and insulating layers, as well as 3 4 a gate dielectric for multi-layer “semiconductor-dielectric” 350 400 450 500 structures. Producing such substrates will allow integrating (nm) GaN-based optoelectronics with a well-developed silicon and gallium arsenide electronics and optoelectronics. Magnetron Figure 14: Photoluminescence spectra of GaN ﬁlms (300 K) on and laser sputtering were used for deposition of ﬁanite ﬁlms GaAs substrate with buﬀer layers: porous GaAs (1) and double buﬀer-ﬁanite on porous GaAs (2). on silicon and gallium arsenide Intensity (cps) Intensity (cps) Intensity (cps) 14 Advances in OptoElectronics 3.4. Fianite Films on Porous Si and GaAs. With the purpose (i) optic refractive index n ∼ 2.1 ÷ 2.2; to improve quality of ﬁanite ﬁlms and its adhesion to Si and (ii) dielectric constant ε ∼ 25; GaAs substrates, opportunities of the use of porous layers of (iii) absence of defects of porosity type (in 30 mm diame- the material were studied. ter sample). The following results were obtained: (i) appropriate regimes of deposition of porous GaAs layer on GaAs (111) substrates of n-and p-conduc- 3.6. Laser Sputtering Technique. Experimental installation for deposition of ﬁanite ﬁlms was a sputtering system tivity types were developed; composed by a vacuum device and excimer laser. The system (ii) appropriate regimes of deposition of the uniform has been designed and manufactured in IPM RAS. mirror-ﬂat ﬁanite layer on GaAs (111) substrates of Operational oxygen pressure was maintained by vacuum 18 × 18 mm size were established; system supplied with a mechanical pump and CHA-2 letting (iii) it has been demonstrated that the use of the porous system. Evaporation of the target was performed by LPX200 layers allowed an improvement of adhesion of ﬁanite eximer laser radiation working on KrF mixture. Wavelength with GaAs layers; of the radiation was 248 nm, pulse duration 27 ns, the pulse energy 350 MJ (pulse power 1.3 × 10 W), and repetition (iv) the samples of ﬁanite/GaAs and ﬁanite/Si epitaxial frequency 50 Hz. Optical system providing a focusing of substrates have been obtained for subsequent growth III the laser beam on the target surface consisted of quartz of A N ﬁlms. prisms and 30 cm focal distance lens. The laser beam spot High mechanical and chemical stability of ﬁanite and on the target surface was 1 × 4mm . The energy density absence of pores open the prospects of its application as on the target surface was ∼10 J/cm . The distance between protective and stabilizing coating for various substrates. the target and substrate was 60 mm. Cylindrical targets of 15–20 mm diameter and 10–30 mm length were used in the installation. In order to prevent local overheating of 3.5. Magnetron Sputtering Technique. Magnetron systems are the target and to provide a uniform material drift rotation related to diode-type sputtering systems. The sputtering an axial movement of the target was used. Possibility of occurred due to bombardment of a target surface by gas conducting pre- and postgrowth annealing under oxygen ions (usually Ar) forming in plasma of anomalous glow atmosphere at 10 Pa–100 kPa pressure and at up to 750 C discharge. Material ions knocked out the target subjected temperature is a peculiarity of the installation. to the bombardment are captured by the magnetic ﬁeld Ceramic target of (ZrO ) (Y O ) with x = 0.1 2 1−x 2 3 x and maintained complex cycloidal movement by closed composition was used for deposition of ﬁanite ﬁlms. The trajectory in vicinity of the target surface. High sputtering deposition was carried out on Si and GaAs substrates heated rate, which is a feature of magnetron systems, is achieved to 600–800 C temperature under oxygen atmosphere at by an increase of the ion current density due to localization approximately 10 Pa. The growth rate of YSZ ﬁlms was about of plasma by means of high transverse magnetic ﬁeld. The 0.02 nm per pulse. Contactless heater of substrates (heating increase of sputtering at simultaneous decrease of actuation by irradiance) was an original peculiarity of the sputtering gas pressure allows a signiﬁcant decrease of contamination system. The heater comprises vertically positioned quartz of the ﬁlms by alien gas impurities. Fianite was grown up on tube (of 30 mm inner diameter) supplied with refractory Si and GaAs substrates using unbalanced magnetron system. stainless steel heating coil on its outer surface with up to Fianite crystals were used as a target. Si substrate subjected to 1 kW power of the heater. Monitoring and maintenance of the sputtering was heated by IR radiance. Preparation of the the assigned temperature (with ±5 C precision) were carried substrates included degreasing, removing of the oxide, and out using precise regulating device and Pt-Rh thermocouple passivating of the surface in ammonium-peroxide solution. positioned under the heating coil. A substrate was ﬁtted in Optimization of the conditions of the growth of ﬁanite ﬁlms a holder and positioned inside of the quartz tube. Loading on Si substrates was carried out by varying of the sputtering of substrates and oxygen supply was maintained through the rate, temperature of the substrate, and residual gas pressure. upper end of the tube. Bombardment of the target leads to dissociation of zirconium and yttrium oxides to ZrO, Zr, YO, Y, and O . Technology of growth of dielectric ﬁanite ﬁlms using the That is why such parameters as sputtering rate and residual laser sputtering consists of the following stages. gas pressure considerably inﬂuence stoichiometry of the (1) A substrate is loaded to the sputtering system and the resulting ﬁlm. Energy of the evaporating particles is rather vacuum chamber is evacuated up to ∼1Pa residual low (∼0.5–10 eV); so for the epitaxial growth of ﬁanite ﬁlm, pressure. a high temperature of Si substrate and optimal rate of the condensate supply are necessary. (2) Letting-to-oxygen is maintained up to the pressure The ﬁanite ﬁlms were studied by means of scanning required. electron microscopy, ellipsometry, and CV-parameters mea- surement techniques. The ﬁlm parameters were found as (3) Rotational movement drive of the target is switched follows: on. Advances in OptoElectronics 15 (4) A substrate is heated up to deposition temperature. usually used at ﬁanite growth. As it has been shown by calculations, ﬁanite should not react with silicon substrate to (5) The eximer laser (the pulse energy 350 MJ, repetition form SiO , which has low dielectric constant value, at a direct frequency 50 Hz) is switched on and the sputtering is contact [45]. However, in practice, it is very diﬃcult to avoid started. the formation of this ﬁlm at ﬁanite deposition or subsequent (6) Followed by the achievement of the assigned thick- high-thermal treatment [46, 47]. Therefore, a development ness of the ﬁlm, the laser is switched oﬀ. of special technological tools is necessary. One of the routes (7) Followed by the end of the ﬁlm growth, the chamber to solve the problem has been suggested by the authors [48]. Thin Zr or Y layer was deposited on Si substrate before is ﬁlled with oxygen up to the pressure required. ﬁanite deposition. The metals absorb oxygen from SiO layer (8) The structure is annealed. because free energy of both ﬁanite and Y O formation is 2 3 The substrate heater is switched oﬀ and the substrate is lower than of SiO one [49]. That leads to a decrease of the layer thickness. cooled to room temperature. Second, oxygen from ﬁanite layer readily diﬀuses to silicon substrate or reacts with silicon surface. Secondary 3.7. Initial Stages of Deposition and Structure of Fianite Buﬀer phases occurring as a result of the reaction disturb silicon Layers on Si and GaAs Substrates. The application of ﬁanite crystal lattice and hinder a perfect growth. Under these cir- as a buﬀer layer will present a solution route to another very III cumstances, ﬁanite layers on Si substrates are of amorphous important problem: epitaxy of A N compounds on Si and or polycrystalline structure. At the development of gate GaAs substrates having large dimensions, high quality, and dielectric technology, these issues are of peculiar importance low net cost. because thickness of the last layer is about some nanometers. Single-crystalline heteroepitaxial ﬁanite ﬁlms of 1000 A Therefore, the above data show that the problem of thickness were grown on silicon substrates of up to 50 mm 2 deposition of ﬁanite ﬁlms on Si substrates is of great interest. diameter in vacuum chamber at p ∼ 2·10 Pa pressure, The problem of improvement of quality of the layers seems to sputtering rate V ∼ 60 A/min, and substrate temperature ◦ be very urgent because of a number of principal diﬃculties T ∼ 800 C. occurring due to peculiarities of physical-chemical proper- The studies have shown that the ﬁlm became continuous ties of the materials resulting in reactions at the growth and as from 100 A thickness. subsequent thermal treatment stages. The synthesis of perfect X-ray structural studies of ZrO -Y O /Si structures 2 2 3 ﬁanite ﬁlms on Si requires a development of special methods have shown that the ﬁanite ﬁlm was single phased and to decrease the inﬂuence of amorphous SiO layer at the consisted of two layers with diﬀerent rocking curve val- substrate-layer interface. ◦ ◦ ues: 0.20 for the upper layer and 0.96 for the lower one. Epitaxial relation between the ﬁlm and the substrate 3.9. Characterization of Fianite Films. The ﬁlms were studied was (100)[100] Si//(100)[100]ZrO -Y O . The relation was 2 2 3 established using diﬀraction measurements under the fol- by means of scanning electron microscopy, ellipsometry, and CV-parameters measurement techniques. lowing regimes: Θ/2Θ scanning (simultaneous rotation of the detector and sample over goniometer axis) and Ψ- scanning (rotation of the plate in a proper plane at ﬁxed 3.9.1. Capacity-Voltage Characteristic Measurements of the detector position). The former regime was used to determine “Fianite-on-Silicon” Structures. The capacity-voltage (CV) orientation of the composition plane, the latter-mutual characteristics of the structures supplied with ﬁanite ﬁlms orientation of unit cells of the ﬁlm, and the substrate in the deposited on p-Si and n-Si substrates were measured. composition plane. Capacity measurements provide evaluation of dielectric Spectra of the Ψ-scanning of (ZrO -Y O )/Si structure 2 2 3 properties of ﬁlms under the study: dielectric constant ε for asymmetric (422) reﬂection of the ﬁlm (b) and the and dielectric loss tgδ. The application of a multifrequency substrate (a) are shown in Figure 15. device allows the determination of frequency dependencies The absence of additional peaks and high peak maxi- of dielectric constant and high-frequency loss in dielectric mum-to-background ratio (∼10 ) are the evidence for ZrO - ﬁlms. Since the dielectric ﬁlm is deposited on a semicon- Y O layer is a perfect single-crystal ﬁlm. The ﬁanite buﬀer 2 3 ductor, a MIS structure (metal-insulator-semiconductor) is III layers grownonSiand GaAs were used forA N compounds formed, so the CV-measurement provides additional infor- epitaxy. mation concerning the semiconductor and the dielectric- semiconductor interface, namely, type of the semiconductor 3.8. Some Diﬃculties in Deposition of Fianite Films on Silicon conductivity (n or p) and concentration of the dopant, ﬂat Substrate. Growth of ﬁanite-on-silicon structures of high band barrier voltage V , density of boundary states, and a fb quality featuring with sharp interfaces is associated with charge induced in the dielectric. signiﬁcant diﬃculties because of a number of principal The device used for CV-measurements allowed deter- problems. mining the capacity and high-frequency conductivity of First, silicon surface readily undergoes transformation the structures, as well as its dependency on the applied into SiO amorphous layer either due to interaction with voltage. The measurements were carried out at 500 KHz and oxygen-containing ﬁanite ﬁlm or oxidative atmosphere 1 MHz frequencies. Direct potential bias range was ±40 V. 16 Advances in OptoElectronics 100 100 0 45 90 135 180 225 270 315 360 0 45 90 135 180 225 270 315 360 ◦ ◦ Ψ ( ) Ψ ( ) i i (a) (b) Figure 15: Ψ scanning spectra for (422) reﬂection of YSZ substrate (a) and the ﬁlm (b). Thermally sputtered Al of 1 mm surface diameter was used as the contacts. The results obtained are shown in Figure 16. “Al-ﬁanite-Si” MIS structure parameters: ﬂat band bar- rier voltage –4 V for 180 nm ﬁlm and 1.5 V for 20 nm ﬁlm; 12 −2 density of the boundary state charge ∼+10 cm . 3.9.2. Investigation of ZrO Films on Si and Ge Substrates by Means of Scanning Electron Microscopy. The ZrO ﬁlms were studied using scanning electron microscopy. All of the ﬁlms studied were porous-free. Since the square of the samples −10 −8 −6 −4 −20 2 4 6 8 10 studied was 5-6 cm , it is possible to consider the porosity −2 Potential bias (V) value at least not exceeding 0.15–0.2 cm . For comparison, −2 it is worth to mention that porosity of SiO ﬁlms is 4–8 cm . Figure 16: CV-characteristics of ﬁanite-on-p-Si sample. Therefore, it is possible to consider ZrO ﬁlms as a protective layer for Ge devices actually superior SiO ﬁlms because its porosity decreased in 1.5–2 orders of magnitude. that formation of larger elements of the relief occurred The study of morphology of the ﬁlms deposited by by enlargement of such particles. The reasons of local magnetron sputtering technique at high magniﬁcation has enlargement (formation of spherical hills) can be gradients shown its satisfactory homogeneity. Some regions of the of temperatureand mass transfer,aswellasoccurrenceof surface featured by a relief composed by quasi-spherical hills impurities. The observations allowed reﬁning the conditions of 500–600 nm in diameter and exhibiting lateral periodicity. of the sputtering of ZrO andﬁaniteﬁlmsinorder to Analytical study of the ﬁlms has shown an absence of minimize surface roughness. inclusions of impurities. An attempt to study the mechanism of formation of the ﬁlms with the purpose to optimize the conditions of 3.10. Fianite as a Gate Dielectric. Recently, a sharp surge of interest in the use of ﬁanite as a gate dielectric in CMOS magnetron sputtering was done using electron microscopy (JSM JEOL 5910 LV). The particles were identiﬁed by means technology has been observed. It is associated with an increase of leakage current at the use of conventional SiO of electron probe. The ﬁlm was removed by polishing using 2 by increasing the integration level. That requires a change of diamond paste with 2.5–4 μm particle size. This abrasive SiO over dielectrics with higher dielectric constant (high-k size was chosen to minimize decreasing particle size of the 2 materials) [30, 32, 33, 45]. The resent studies have limited ﬁlm constituents at the polishing. The obtained material possible alternatives to ﬁanite, HfO ,ZrO , and its silicates. was ﬂushed by ethanol (9–12 purity grade “for microelec- 2 2 For example, ZrO has high dielectric constant value, good tronics”) and the suspension was put in plastic syringes (1 mL). In order to disintegrate aggregates, ultrasonic (US) dielectric properties (5.8 eV energy gap width), and rather good crystallochemical matching with Si [50] (see Table 2). treatment was carried out. The US dispersion was conducted using “Sapphire 3 M-1.3” US device with 35 GHz operational Intel Corp., one of the leaders of the world electronics, has demonstrated that the change of SiO over HfO as a gate frequency. The syringes were inserted to the device chamber 2 2 ﬁlled with water. The chamber was thermostated at 27 C. dielectric in 45 nm technological process allows decreasing leakage currents, (which became a serious problem for Followed by 3 min of the US treatment, the suspension transistors) by more than two orders of magnitude [51]. was aspirated onto conductive (graphitized) ribbon for subsequent microscopy study. The study has shown that Comparison of ﬁanite ﬁlms [33]and SiO with electrical the largest constituents of the zirconia ﬁlm were quasi- equivalent oxide thickness of about 1.46 nm, has shown that spherical particles of 50–100 nm size that explained X-ray the leakage current for ﬁanite was four orders of magnitude amorphous nature of the ﬁlm. It is possible to suggest lower than that of conventional SiO gate oxides. Ncp 10 s Ncp 10 s Capacity (pF) Advances in OptoElectronics 17 Table 3: Parameters of growth and annealing of the ﬁanite-on-Si ﬁlms. Sample T of growth, C Annealing, 600 C, 10 min Film thickness, nm Substrate z1 Room Without annealing ∼20 Si B z2 Room Vacuum ∼20 Si B z3 Room Oxygen ∼20 Si B z4 Room Oxygen ∼20 Si Sb z5 600 Oxygen ∼20 Si B Table 4: Optimal modes of ﬁanite and ZrO sputtering. The hysteresis and interface state density in this ﬁlm was 2 11 −1 −2 measured to be less than 10 mV and 2.0 × 10 eV cm . Target material Fianite ZrO Thus, such crystalline oxide on semiconductor could be used Installation Z-400 Z-550 for future generation of semiconductor-based devices. Target diameter ∅ 70 mm ∅ 203 mm It is worth to note that quality of the synthesized ﬁanite, −3 −3 Argon pressure 5 ∗ 10 mBar 5 ∗ 10 mBar as well of the interfaces, is very important for integration of Power ∼500 Wt ∼400 Wt such a dielectric to the CMOS technology currently in use. ˚ ˚ Synthesizing of ﬁanite-on-silicon structures of high Film growth rate 100 A/min ∼50 A/min quality featuring with sharp interfaces is associated with signiﬁcant diﬃculties described above. One of the routes to solve this problem is in application magnetron power, plasma is unstable (“blinking plasma”); of low-temperature growth and annealing regimes, as those, in case of larger values of discharge power, the growth rate which were used in the series of experiments described below, increases, but irregularity of the surface patterns and growing type of a substrate, and the annealing media were also varied. ﬁlm coarse-graining were observed on a number of samples. Conditions of the synthesis of the ﬁanite/Si structures are Fianite sputtering requires higher power than in case of given in Table 3. XRD technique has shown that ﬁanite layers ZrO , at the same time the growth rate was twice as much obtained by laser deposition at room temperature were of thanincaseofZrO . amorphous structure. The developed technique of magnetron sputtering made Subsequent postgrowth recrystallization annealing it possible to vary the ﬁanite ﬁlm thickness between 600 resulted in arising of a polycrystalline phase in the ﬁlm. At and 2000 A. The optimization of the sputtering modes the same time, the layers sustained mirror ﬂat and uniform. allowed producing of Ge and Si plates with ﬁanite ﬁlms Proﬁle of the surface of z4 sample (Table 4) obtained using of satisfactory quality. Ge plates with ﬁanite ﬁlms were Talysurf interference microscope is shown in Figure 17(a). used to try out further operations of the device structures Roughness of this ZrO surface was estimated as Sq = production: photolithography and etching. 0.852 nm that does not practically diﬀer from roughness of the Si substrate used for the ﬁanite growth (Sq = 0.7877 nm). 3.12. Protective and Stabilizing Properties of Fianite Films Preliminary studies of gate properties of thin (10– on Ge. Inorganic dielectric coatings are usually used for 15 nm) ﬁanite ﬁlms obtained by laser deposition on Si passivating and protection of p-n transition surface, as substrates have been carried out. The studies conducted on shielding and thermal compensation layers at ion implanting the test structures with deposited Al contacts have shown and for interference antireﬂecting protection. Passivation of that thin ﬁanite ﬁlms featured with low values of loss the surface is the most important issue for manufacturing −12 2 currents, minimum values being 10 A/cm at 1 V voltage of germanium photodiodes because natural GeO and GeO (Figure 17(b), samples z3 and z4). oxides are unstable and, so, cannot be considered as the only passivating coatings. It is one feature distinguishing Ge and Si devices (the latter have stable and rather eﬃcient 3.11. Fianite and ZrO as Protective and Stabilizing Layers on coating formed by its own SiO oxide). This oxide ﬁlm Ge and Si Substrates and Multilayer Structures deposited from a gas phase is of the most frequent use 3.11.1. Deposition Modes. Fianite and zirconium dioxide for photodiodes, with p -n-structure. It has positive charge and by attracting electrons to the surface prevents growth ﬁlms were deposited by magnetron sputtering technique, 2 types of vacuum evaporation Leybold Heraeus units of p-channels thus decreasing probability of generation in the layer. It is worth to note that for improved reliability (Z-400 and Z-550) with diﬀerent target dimensions were used: 70 mm in diameter for ﬁanite and 203 mm—for ZrO and stability of characteristics of photodiodes, it is necessary 11 −2 −1 (Table 4). to maintain surface state density at 10 cm eV level. However, this passivating technique is far from ideal because High-frequency and direct voltage modes of sputtering of the high porosity of SiO ﬁlms that decreases humidity were tested. By using the latter mode it was impossible to 2 resistance and reliability of the device. provide suﬃcient ﬁlm growth rate, so HF sputtering mode (13.56 MHz) was chosen. The optimal modes of ﬁanite and In order to improve dielectric properties of the protective ZrO sputtering are also shown in Table 4.Incaseoflow coating, ﬁanite ﬁlms deposited by magnetron sputtering were 2 18 Advances in OptoElectronics −1 Z2 −2 Z5 −3 −4 −5 Z1 −6 −7 −8 Length = 101 μm; Pt = 3.995 nm; scale= 10 nm −9 Z3 Z4 4 −10 −11 −12 −2 −4 −13 0 10 20 30 40 50 60 70 80 90 100 01 2 3 (μm) V (A) (a) (b) Figure 17: Surface roughness of ﬁanite ﬁlm on Si substrate, sample z4 (a); and leakage current of Al/ﬁanite/Si structure (b) samples z1–z5 were prepared under diﬀerent conditions. used. The opportunity of its application for maintaining high-quality practically porous-free protective coating has been conﬁrmed earlier by the experiments. It has been demonstrated that the use of ﬁanite protective layer in Ge-structures instead of SiO eliminated pulse noise and thus considerably improved photoelectric and performance characteristics of these devices. It has been established that the improvement was related to a more uniform nature of ﬁanite ﬁlms, in particular, absence of pores, in comparison with SiO ﬁlms, which contain defects 10 in form of pores. 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 3.13. Some Properties of the Device Structures Supplied Wavelength λ (μm) with Zirconium Dioxide Films. Photoelectric characteristics Figure 18: The dependency of the reﬂection on wavelength of and noise of germanium photodiodes supplied with ZrO silicon sample coated with ZrO ﬁlm of 1200 A thickness. and SiO ﬁlms described above have been investigated. Monochromatic sensitivity of these photodiodes is typical for germanium devices and equals to 0.5-0.6 A/W (at 1.06 and using these ﬁlms have demonstrated the advantages of 1.55 μm wavelengths). The change SiO over ZrO resulted 2 2 zirconia-based solid solutions in application to photosensi- in somewhat decrease of a dark current (on average for 10%). tive apparatus technology. Main improvement of the photodiodes quality achieved due to the application of ZrO ﬁlms was revealed at the noise studies. Under the voltage exceeding operational one (that 3.14. Studies of Optical Properties of ZrO Films. Optical corresponds to accelerated reliability testing conditions), the refraction of ZrO equals to 1.98 ÷ 2.1, that is, close check samples with SiO ﬁlms have shown pulse noise of 2 to ﬁanite one; therefore this material is also promising telegraphic type in the oscillogram, which can be associated for antireﬂection coatings. Determination of the refraction with processes of energizing-deenergizing of the surface constant n and monitoring of the ﬁlm thickness d were conducting channels [51]. The defects occurring because of carried out using ellipsometry technique. The experimentally the presence of pores in SiO ﬁlms are probable cause of 2 determined values of d depended on duration of the ﬁlms arising of the channels. In the batch with ZrO protective ˚ ˚ 2 growth and varied within 600 A–1100 Arange. ﬁlms, only shot noise, which is in principle unavoidable, The ﬁlms obtained have shown rather high refraction was observed. More detailed results of the device studies are constant ∼2 ÷ 2.1. These values were signiﬁcantly higher presented in [52]. than that of SiO (1.45). Thus, the studies performed on ﬁanite and zirconium In theory, considering an incident beam from air (vac- dioxide ﬁlms as well as on the device structures developed uum), it is possible to decrease the reﬂection to zero when (nm) I (A) Reﬂectance (%) Advances in OptoElectronics 19 0.32 0.4 0.3 0.38 0.36 0.28 0.34 0.26 0.32 0.24 0.3 0.22 0.28 0.2 0.26 0.18 0.24 0.16 0.22 0.2 0.14 0.18 0.12 0.16 0.1 0.14 0.08 0.12 0.06 0.1 0.04 0.08 0.02 0.06 0.04 0.02 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 λ (μm) 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 λ (μm) Ge Si (a) (b) Figure 19: Experimental (1) and theoretical (2) dependencies of the reﬂection on wavelength in Ge-ﬁanite antireﬂecting ﬁlm system (1300 A) (a); experimental dependencies of the reﬂection of ﬁanite ﬁlm on Si and Ge (b). the refraction constant of an antireﬂecting ﬁlm corresponds the corresponding thickness of a ﬁlm d) at n = n ,where d f to the following equation: n -optical refraction constant of a semiconductor. Since for Si and Ge the constants are equal to 3.7 and 4, respectively, n = n , (1) the reﬂection is completely eliminated at n = n ≈ 2. d f Therefore, a dielectric having its optical refraction constant where n -refraction constant of a semiconductor. In case of n = n ∼ 2(at n = 3.7 ÷ 4) canbeconsideredasan d f f Si and GaAs, n ∼ 3.5 ÷ 4, thus n ∼ 1.9 ÷ 2. Therefore, f f optimal material for the antireﬂecting ﬁlm for solar cells and ZrO ﬁlms obtained actually satisfy perfect antireﬂection 2 the other photosensitive devices. Theoretically, at the ﬁlm for Si and GaAs-based devices from the viewpoint of n. thickness, which is equal to a quarter of optical wavelength Moreover, the diﬀerence in n-values of SiO and ZrO ﬁlms 2 2 W = λ/4n , such dielectric allows a complete elimination of provides an opportunity for the antireﬂection over a broad the reﬂection loss (R = 0). spectral range due to application of binary SiO +ZrO 2 2 The refraction constant of SiO (n = 1.47) is consid- 2 d antireﬂecting coatings. The dependency of the reﬂection erably lower than that value. At this n value it is impossible constant on wavelength of silicon sample coated with ZrO to maintain the reﬂection loss lower than 10%. Refraction ﬁlm of 1200 A thickness is presented in Figure 18.Theoretical constants of ﬁanite and ZrO are within (2.15 ÷ 2.18) and absorption minimum corresponds to λ = 4n · d = 4 · 2.1 · (2.13 ÷ 2.2), respectively, that is close to the above optimum 0.12 ≈ 1 μm. value. Thus, providing an evidence that ﬁanite and ZrO are As it is apparent from Figure 18, the reﬂection minimum very promising as antireﬂecting coatings for solar cells and III V was approached at λ = 0.97 μm. Thus, the experimental min the other photosensitive devices based on Ge, Si, and A B results are in conformity with the theory practically com- compounds. plete. Experimental dependencies of antireﬂection (as depen- Therefore, ZrO ﬁlm ensures high antireﬂection quality: dencies of the reﬂection on wavelength) of ﬁanite ﬁlms on Si at λ , the reﬂection loss does not exceed 2-3%. The data min and Ge have been plotted (Figure 19). obtained conﬁrm that ZrO is an excellent material for The plots apparently demonstrate that the reﬂection antireﬂecting ﬁlms, as well as ﬁanite. drops to 0–1.5% in the minima. Experimental study of antireﬂective properties of ﬁan- ite oxide applied to Ge was performed. By the reason 4. Fianite as Antireﬂecting Layer for that germanium photodetectors are designed for detecting Solar Cells radiation generated by lasers with wavelengths λ = 1.06, 4.1. Antireﬂecting Properties of Fianite Film on Ge and Si. In 1.3, and 1.54 μm, thickness of the antireﬂective ﬁanite ﬁlm theory, it is possible to eliminate the reﬂection completely (at was chosen as W = 1300 A; such thickness provides for R, rel. units R, rel. units 20 Advances in OptoElectronics 0.12 0.12 0.11 0.11 0.1 0.1 0.09 0.09 0.08 0.08 0.07 0.07 0.06 0.06 0.05 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.01 0.01 0 0 0.4 0.5 0.6 0.7 0.8 0.9 1 0.4 0.5 0.6 0.7 0.8 0.9 1 1 3 2 4 (a) (b) (c) ˚ ˚ Figure 20: Antireﬂecting properties (reﬂection spectra) of ﬁanite ﬁlms of 580 A (a) and 1050 A (b) thickness. The experimental data were obtained on the industrial items s (c) of Si solar cells of “4 x 4” size. minimal reﬂection losses in the considered wavelength range As it is shown in Figure 19(a), in the range of funda- λ = 1.06–1.54 μm. Figure 19(a) shows the comparison of mental absorption (for λ< 1.65 μm), the experimental curve experimental (thin line) and theoretical (bold line) R(λ) 1 coincides with the theoretical curve 2. Some discrepancy curves. The theoretical R(λ) curve was calculated using the at higher wavelengths (λ> 1.65 μm) appears due to deep following formula: penetration of such radiation and its reﬂection from the back surface. It is important that at the optimal wavelength R =1 (λ = 1.12 μm), ﬁanite ﬁlm provides for ideal antireﬂective properties, the reﬂection is actually absent. In rather large n n (2) range 0.88–1.55 μm, into which radiation wavelengths of the − . 2 2 2 2 2 most wide spread lasers fall, the losses for reﬂection do not n n +1 − n −n n −1 sin (2πn W/λ) f d d f d d exceed 10%. According to the above formula, reﬂection may fall The experimental dependences of enlightenment (the practicallytozeroatthe optimalvalue of n (note that dependence of reﬂectance on the wavelength) of cubic in case of SiO antireﬂective ﬁlm, for which n = 1.47, 2 d zirconia ﬁlms on Si and Ge (Ge by its optical properties is it is impossible to obtain reﬂection lower than 10%). The similar to GaAs) exhibit excellent antireﬂective properties of minimal reﬂection is achieved at the following wavelength cubic zirconia (Figure 19(b)). As is evident from the graphs, λ : the minimum reﬂection can drop to 0-1, 5%. Position of the min minimum depends on the thickness of the ﬁlm. When it gets λ = 4Wn . min d (3) thinned twice, the minimum would be in the solar spectrum. Advances in OptoElectronics 21 Plateau in the curve shows the reﬂection from the back side [2] S. Yu. Kuz’minov, E. E. Lomonova, and V. V. Osiko, Cubic Zirconia and Skull Melting, Cambridge International Science, of the substrate in the transmission range for Si. So the gain UK, 2009. due to the use of the antireﬂecting ﬁanite ﬁlm reaches 20– [3] V. V. Osiko, M. A. Borik, and E. E. Lomonova, “Synthesis of 30%. refractory materials by skull melting technique,” in Handbook So, it was experimentally proved that for 1300 A thick of Crystal Growth, pp. 433–469, Springer, 2010. ﬁanite ﬁlm, reﬂection may actually drop to zero in the [4] I. Golecki, H. M. Manasevit, L. A. Moudy, J. J. Yang, and J. wavelength range λ = 1.06–1.54 μm. E. Mee, “Heteroepitaxial Si ﬁlms on yttria-stabilized, cubic A new, unusual application of ﬁanite as a reﬂecting zirconia substrates,” Applied Physics Letters, vol. 42, no. 6, pp. ﬁlm (in contrast to antireﬂecting!) was suggested. 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References

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Silicon heterostructures on fianite substrates,

G. Shengurov, V. N. Shabunov, A. N. Buzynin et al.
Epitaxial films of GaAs and GaN on fianite substrate,

A. N. Buzynin, V. V. Osiko, E. E. Lomonova, N. Yu. Buzynin, and A. S. Usikov
Epitaxial GaN and Ga Nx A s1−x films on monolithic and porous GaAs substrates with fianit sublayer,

A. N. Buzynin, V. V. Osiko, K. Yu. Voron'ko et al.
(111) and (100) YSZ as substrates for indium nitride growth,

P. A. Anderson, C. E. Kendrick, R. J. Kinsey et al.
Electrical properties of crystalline YSZ films on silicon as alternative gate dielectrics,

S. J. Wang, C. K. Ong, S. Y. Xu et al.
Rapid thermal annealing effect on crystalline yttria-stabilized zirconia gate dielectrics,

S. J. Wang and C. K. Ong
Epitaxial films of III-V compound on fianite substrates,

A. N. Buzynin, V. V. Osiko, E. E. Lomonova et al.
X-ray photoemission spectroscopy determination of the InN/yttria stabilized cubic-zirconia valence band offset,

P. D. C. King, T. D. Veal, S. A. Hatfield et al.
RF-MBE growth and structural characterization of cubic InN films on yttria-stabilized zirconia (0 0 1) substrates,

T. Nakamura, Y. Tokumoto, R. Katayama, T. Yamamoto, and K. Onabe
Epitaxial structures of AIIIBV materials on fianite,

A. N. Buzynin, V. V. Osiko, Y. K. Voronko et al.
Growth on GaN and GaAs on fianite by MOCVD capillary epitaxy technique,

A. N. Buzynin, V. V. Osiko, Y. N. Buzynin, and B. Pushnyi
Epitaxial films of GaAs and GaN on fianite substrate,

A. N. Buzynin, V. V. Osiko, E. E. Lomonova, N. Yu. Buzynin, and A. S. Usikov
SOI technology for the GHz era,

G. G. Shahidi
Fianite: a multipurpose electronics material,

A. N. Buzynin, V. V. Osiko, Y. N. Buzynin et al.
MOVPE GaN grown on alternative substrates,

R. Paszkiewicz, B. Paszkiewicz, R. Korbutowicz et al.
Laser characterization of sapphire defectts,

A. N. Buzynin and V. P. Kalinushkin
New technique of laser characterization of sapphire and fianite crystals,

A. N. Buzynin and V. P. Kalinushkin Abstracts of the
Predominant orientation of crystals on a substrate and the effect of scratches,

N. N. Sheftal and A. N. Buzynin
Oriented crystal growth on amorphous substrates using artificial surface-relief gratings,

H. I. Smith and D. C. Flanders
Reduction of defect density in GaN epilayer having buried Ga metal by MOCVD,

M. Sumiya, Y. Kurumasa, K. Ohtsuka, K. Kuwahara, Y. Takano, and S. Fuke
Application of surface electron beam induced voltage method for the contactless characterization of semiconductor structures,

E. I. Rau, A. N. Zhukov, and E. B. Yakimov
Growth and defects of GaAs and InGaAs films on porous GaAs substrates,

A. N. Buzynin, Y. N. Buzynin, A. V. Belyaev, A. E. Luk'yanov, and E. I. Rau
SOI technology for the GHz era,

G. G. Shahidi
Electrical properties of ZrO2 gate dielectric on SiGe,

T. Ngai, W. J. Qi, R. Sharma et al.
MOCVD of HfO2 and ZrO2 high-k gate dielectrics for InAlN/AlN/GaN MOS-HEMTs,

S. Abermann, G. Pozzovivo, J. Kuzmik et al.
Crystalline zirconia oxide on silicon as alternative gate dielectrics,

S. J. Wang, C. K. Ong, S. Y. Xu et al.
Electrical properties of crystalline YSZ films on silicon as alternative gate dielectrics,

S. J. Wang, C. K. Ong, S. Y. Xu et al.
Heteroepitaxial growth of yttria-stabilized zirconia (YSZ) on silicon,

H. Fukumoto, T. Imura, and Y. Osaka
Yttria-stabilized zirconia (YSZ) heteroepitaxially grown on Si substrates by reactive sputtering,

T. Hata, K. Sasaki, Y. Ichikawa, and K. Sasaki
Epitaxial fianit films on Si and GaAs,

A. N. Buzynin, V. V. Osiko, Y. K. Voronko et al.
Widening temperature range of epitaxial growth of YSZ films on Si [100] under magnetron sputtering,

V. G. Beshenkov, A. G. Znamenskii, V. A. Marchenko, A. N. Pustovit, and A. V. Chernykh
Interfacial properties of a hetero-structure YSZ/p-(1 0 0)Si prepared by magnetron sputtering,

S. Jeon, M. Takanori, A. Unno, K. Wasa, Y. Ichikawa, and H. Hwang
Heteroepitaxial growth of CeO2 thin film on Si(001) with an ultra thin YSZ buffer layer,

N. Wakiya, T. Yamada, K. Shinozaki, and N. Mizutani
Single domain epitaxial growth of yttria-stabilized zirconia on Si(1 1 1) substrate,

S. Kaneko, K. Akiyama, T. Ito et al.
Pulsed laser deposition of Zr1−xCexO2 and Ce1−xLaxO2−x/2 for buffer layers and insulating barrier in oxide heterostructures,

R. Lyonnet, A. Khodan, A. Barthélémy et al.
Thickness determination of large-area films of yttria-stabilized zirconia produced by pulsed laser deposition,

N. Pryds, B. Toftmann, J. B. Bilde-Sørensen, J. Schou, and S. Linderoth
Excimer pulsed laser deposition and annealing of YSZ nanometric films on Si substrates,

A. P. Caricato, G. Barucca, A. Di Cristoforo et al.
Effect of deposition temperature on the growth of yttria-stabilized zirconia thin films on Si(111) by chemical vapor deposition,

S.-C. Hwang and H. S. Shin
Visible-blind GaN Schottky barrier detectors grown on Si(111),

A. Osinsky, S. Gangopadhyay, J. W. Yang et al.
Depth dependence of the tetragonal distortion of a GaN layer on Si(111) studied by Rutherford backscattering/channeling,

M. F. Wu, C. Chen, D. Zhu et al.
Ultraviolet and violet GaN light emitting diodes on silicon,

S. Guha and N. A. Bojarczuk
Wurtzite GaN epitaxial growth on a Si(001) substrate using γ-Al2O3 as an intermediate layer,

L. Wang, X. Liu, Y. Zan et al.
GaN growth on Si(111) substrate using oxidized AlAs as an intermediate layer,

N. P. Kobayashi, J. T. Kobayashi, P. D. Dapkus et al.
Microstructure and photoluminescence of GaN grown on Si(111) by plasma-assisted molecular beam epitaxy,

A. Ohtani, K. S. Stevens, and R. Beresford
SiC rapid thermal carbonization of the (111)Si semiconductor-on-insulator structure and subsequent metalorganic chemical vapor deposition of GaN,

A. J. Steckl, J. Devrajan, C. Tran, and R. A. Stall
Zirconia-based solid solutions-New materials of photoelectronics,

A. N. Buzynin, T. N. Grishina, T. V. Kiselyov et al.

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Applications of Fianite in Electronics

Applications of Fianite in Electronics

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Applications of Fianite in Electronics

Applications of Fianite in Electronics

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