**3.3.1 GaAs on fianite films - MOCVD capillary epitaxy of III-V on fianite**

The investigations showed that continuous GaAs layers on fianite can be obtained only in a very narrow range of epitaxial conditions. In particular, temperature range of 550-600°C is necessary. The minimum thickness of a continuous layer was 1.5-2.0 µm. The epitaxial films had polycrystalline structure and rough surface. Structural and electrical properties of GaAs films could be improved using capillary epitaxy. The essence of this method is that a thin (less than 50 nm) film of an III-group element is initially deposited on the fianite surface and then saturated with a V-group component with the formation of a thin continuous epitaxial III-V layer. After this procedure, the film growth continues to obtain the necessary thickness under conventional epitaxial conditions.

The use of capillary forces in the first (heteroepitaxial) stage of GaAs film formation led to improvement of epitaxial quality. Electron microscopy of the GaAs films at the initial growth stages showed that the transition from the standard MOCVD growth to capillary epitaxy leads to a change in the growth mechanism. Three-dimensional island mechanism changes to the two-dimensional one with propagation of the growth steps (Fig. 9, A). This process is similar to graphoepitaxy [27, 28] from aqueous solutions with addition of surfactants, where an increase in the substrate wettability also significantly improves the quality of graphoepitaxial layers [27] (Fig. 9, B).

In both cases, the height of the crystallization medium (melt or solution) decreases in the initial stage due to the capillary forces. This effect impedes growth of epitaxial nuclei in the direction normal to the substrate surface and facilitates their growth in the tangential direction. As a result, the substrate orienting role increases and a transition to the layer-bylayer growth mechanism occurs with a decrease in the growth step height. As a result, the minimum height of the continuous layer decreases and the film structural quality is improved. It has been shown that the use of capillary force in this method has a positive influence on both the mechanism of epitaxial growth and the quality of AIIIBV epitaxial films. It also reduces the minimum thickness of a continuous layer [17, 19]. Virtually the same approach has now begun to be used with success in the works of other authors in order to obtain AIIIN films on various substrates [29].

The use of capillary epitaxy made it possible to decrease minimum thickness of a continuous GaAs/fianite film to 25 nm and to improve its structural quality and surface morphology. The technique was also efficient for growing other AIIIBV compounds on fianite.

#### **3.3.2 Study of impurities content in GaAs-on-fianite films using mass-spectrometry analysis**

Mass-spectrometry analysis using single crystal GaAs standard curve has shown concentration of the impurities in GaAs-on-fianite films grown using the capillary epitaxy technique to be in the range of 51016–51017сm–3 (Tab. 2). Layerwise mass-spectrometry analysis of the GaAs/fianite structures has shown uniform distribution of the impurities in GaAs film. Somewhat increase of Ca, Na and Cr concentrations in the film-substrate interface seems to be associated with a formation of oxides in the interface.

Fianite in Photonics 145

Impurity Fianite crystal, mass% Fianite substrate, mass% GaAs-on-fianite film,

Al 0.0004 0.001 5x1017 Ca 0.001 0.003 5x1017

Na 0.0001 0.003 2x1017 K 0.0005 0.001 5x1016 Si 0.001 0.015 1x1017

Fe 0.0004 0.0004 5x1016

Cr 1x1016 C 1x1017

In order to obtain flat layers laser sputtering technique was used in the study.

0.15 μm total thickness were deposited using this technique.

fianite substrates electron mobility approaches to 580 cm2/ V×s.

velocity of the surface recombination.

than 4 nm (Sq = 0.003778 μm).

Table 2. Concentrations of the impurities in the crystals, fianite substrates and GaAs films

The studies have shown that it was complicated to obtain thin and homogeneous layers of AIIIBV compounds on fianite substrates. It may be related to rather high mismatching of the lattice parameters of fianite and AIIIBV compounds leading to growth according Volmer-Weber mechanism. Formation of the continuous layer occurred through 3 dimensional nuclei, their subsequent growth and joining. Low nuclei density results in formation of highly inhomogeneous rough surface that hinders subsequent formation of a flat layer. Laser sputtering technique is considered to maintain high nuclei density, so, before joining the nuclei are of sufficiently small size that promotes formation flat

The Q-switched Nd laser and single crystal GaAs and InAs targets were used. The superlattices were grown by optical switching of the layer beam between the targets. Mirror-flat GaSb, GaAs: Sb layers, as well as penta-periodic InAs/GaSb supperlattices of

The X-ray diffraction investigations of GaAs:Sb (111) layers on fianite (111) showed their single-crystal structure (fig. 10a). It was shown that the spectral dependence of photoconductivity of GaSb layers on fianite substrates (fig. 10b) have a maximum of photoconductivity at the edge of fundamental absorption. This effect may be due to high

The width of the rocking curve for these layers as FWHM [GaSb (111)] = 0.23o. The image of the surface of GaAs:Sb (0.2 μm fickness) on fianite is shown in fig. 11a. It is apparent, that the surface of the layer is mirror-flat and sufficiently homogeneous. The microrelief of the layer surface is shown in fig. 11b. According to our estimations roughness of the layer is less

In the penta-periodic InAs/GaSb supperlattices of 0.15 μm total thickness grown on (111)

Mg 0.0005 0.0005

Cu 0.0005 0.0005

Mn 0.0001 0.001 La 0.0006 0.006

continuous layer.

atoms сm–3

Fig. 9. Analogy between capillary epitaxy and graphoepitaxy**:** A - Electron microscopy image of GaAs on YSZ initial stage of growth (20000Х): Conventional MOCVD, height of the islets is up to 3000 nm, left; Capillary epitaxy technique, minimal layer thickness is 50 nm, layers growth is visible, right [17]; B - *Optical microscopy image of NH4 J on amorphous Al graphoepitaxy growth:* without (left) and with (right) the use of surface-active substances, magnification 100Х [27].

#### **3.3.3 The deposition of GaAs, GaSb, GaAs: Sb films and GaSb/InA supper-lattice on fianite substrates by means of laser sputtering**

Our experiments have shown that the conventional "direct" growth of heteroepitaxial films InGaAs on fianite substrates resulted in the films with rough surface. So the buffer layers were elaborated to improve the results. The buffer layer must have very high structural perfection and mirror-homogeneous surface. The multiple experiments were conducted for growth of GaAs, GaSb, GaAs: Sb buffer layers on fianite (100) and (111) substrates as well as well as GaSb/InAs superlattice by using laser spraying. This superlattice is working as a filter which prevents the defects penetration into InGaAs film and first of all, formation of growing dislocation. Furthermore Sb is an effective surfactant [52] which significantly improves the layer morphology.

Fig. 9. Analogy between capillary epitaxy and graphoepitaxy**:** A - Electron microscopy image of GaAs on YSZ initial stage of growth (20000Х): Conventional MOCVD, height of the islets is up to 3000 nm, left; Capillary epitaxy technique, minimal layer thickness is 50 nm, layers growth is visible, right [17]; B - *Optical microscopy image of NH4 J on amorphous Al graphoepitaxy growth:* without (left) and with (right) the use of surface-active substances, magnification 100Х [27].

**3.3.3 The deposition of GaAs, GaSb, GaAs: Sb films and GaSb/InA supper-lattice on** 

Our experiments have shown that the conventional "direct" growth of heteroepitaxial films InGaAs on fianite substrates resulted in the films with rough surface. So the buffer layers were elaborated to improve the results. The buffer layer must have very high structural perfection and mirror-homogeneous surface. The multiple experiments were conducted for growth of GaAs, GaSb, GaAs: Sb buffer layers on fianite (100) and (111) substrates as well as well as GaSb/InAs superlattice by using laser spraying. This superlattice is working as a filter which prevents the defects penetration into InGaAs film and first of all, formation of growing dislocation. Furthermore Sb is an effective surfactant [52] which significantly

**fianite substrates by means of laser sputtering** 

improves the layer morphology.

**A**

**B** 


Table 2. Concentrations of the impurities in the crystals, fianite substrates and GaAs films

The studies have shown that it was complicated to obtain thin and homogeneous layers of AIIIBV compounds on fianite substrates. It may be related to rather high mismatching of the lattice parameters of fianite and AIIIBV compounds leading to growth according Volmer-Weber mechanism. Formation of the continuous layer occurred through 3 dimensional nuclei, their subsequent growth and joining. Low nuclei density results in formation of highly inhomogeneous rough surface that hinders subsequent formation of a flat layer. Laser sputtering technique is considered to maintain high nuclei density, so, before joining the nuclei are of sufficiently small size that promotes formation flat continuous layer.

In order to obtain flat layers laser sputtering technique was used in the study.

The Q-switched Nd laser and single crystal GaAs and InAs targets were used. The superlattices were grown by optical switching of the layer beam between the targets. Mirror-flat GaSb, GaAs: Sb layers, as well as penta-periodic InAs/GaSb supperlattices of 0.15 μm total thickness were deposited using this technique.

The X-ray diffraction investigations of GaAs:Sb (111) layers on fianite (111) showed their single-crystal structure (fig. 10a). It was shown that the spectral dependence of photoconductivity of GaSb layers on fianite substrates (fig. 10b) have a maximum of photoconductivity at the edge of fundamental absorption. This effect may be due to high velocity of the surface recombination.

The width of the rocking curve for these layers as FWHM [GaSb (111)] = 0.23o. The image of the surface of GaAs:Sb (0.2 μm fickness) on fianite is shown in fig. 11a. It is apparent, that the surface of the layer is mirror-flat and sufficiently homogeneous. The microrelief of the layer surface is shown in fig. 11b. According to our estimations roughness of the layer is less than 4 nm (Sq = 0.003778 μm).

In the penta-periodic InAs/GaSb supperlattices of 0.15 μm total thickness grown on (111) fianite substrates electron mobility approaches to 580 cm2/ V×s.

Fianite in Photonics 147

homogeneous AlGaAs/InGaAs/GaAs multi-layer heterostructures with smooth slightly bloom surface were grown on (001) fianite substrates of 50 mm diameter. Roughness of the heterostructure surface measured using Talysurf interference microscope (3-dimensional topography) was 0.25 μm. This structure was grown using «AIXTRON» installation on (100) fianite ellipsoidal substrate of 2 inch major diameter. The surface of multilayer structure is

> n+ GaAs:Si nSi ~6x1018 cm-3 40 nm i-AlxGa1-xAs x~0.24 (>0.23) 25 nm i-GaAs ~0.6 nm

i-GaAs ~0.6 nm i-AlxGa1-xAs x~0.24 4 nm i-GaAs 1 nm i-InyGa1-yAs y~0.18 (<0.2) 11 nm i-GaAs 30 nm i-AlxGa1-xAs x~0.24 50 nm i-GaAs n< 8x1014 cm-3 0,5-0,8 m CP AlAs/GaAs (1 nm/ 2 nm) x 5 GaAs: Sb 100 nm

Fianite substrate 400 m

Structural perfection of AlGaAs/InGaAs/GaAs multi-layer heterostructures on fianite was investigated by means of XRD. DRON-4 device (Ge(004) monochromator, CuK1 radiation) was used. /2 - spectra were recorded at symmetric reflection mode by scanning with 0.1 steps of texture maxima rocking. X-ray diffraction /2 - spectrum of GaAs (001) / fianite (001) is shown in Fig. 12. The peaks of (Zr,Y)O2 (004), 2 = 73.4 substrate and of GaAs(004), 2 = 66.05 buffer layer were recorded. The width of the layer rocking curve FWHM = 1 that is the evidence of a mosaic structure of GaAs layer. The grain-boundary angle was ~ 1 (Fig. 12a). Preliminary conditions of the growth of AlGaAs/InGaAs/GaAs heterostructures on fianite has shown that the use of (111) fianite substrate with GaAs:Sb buffer layer allowed reaching of mirror-flat homogeneous surface and 10-fold decrease of its roughness

Layer-by-layer SIMS analysis of the heterostructures on fianite was carried out using «Shipovnik 3» and «TOF SIMS-5» devices. These devices provide detailed information on elemental and molecular composition in thin sub-surface layers, as well as 3-dimensional analysis. Sputtering was carried out by Cs+,2 keV, raster 250250 μm, negative ion detection mode, the probe beam Bi+, 25 keV, depth resolution DZ > 7 nm. The analysis of the AlGaAs/InGaAs/GaAs heterostructures obtained on fianite (Fig. 12b) has shown that its inner topology was in conformity with the assigned scheme (Tab. 3) of the PHEMT-

rather uniform but its roughness reaches the value of 25 nm.

δ-Si nSi ~4,5x1012 cm-2

Table 3. PHEMT heterostructure for FET operating in 10-40 GHz range

up to 0.025 μm value.

structure.

Fig. 10. X-ray rocking curve of layer GaSb(111)/fianite(111) (a); rocking curve width FWHM GaSb(111) = 0.23o; photoconductivity of GaSb on fianite substrate (b).

Fig. 11. Interference microscope images of surface (а) and the surface relief (b) of buffer layer GaAs:Sb on fianite (Interference microscope Talysurf).

The GaSb layers, as well as InAs/GaSb short-period supperlattices are suitable for the development of IR detectors operating in 2-3 μm range. In our studies they were used as buffers for AIIIN growth on fianite substrates.

#### **3.3.4 Deposition of GaAs, AlGaAs, InGaAs – Based multilayer structures on fianite**

The results on epitaxial growth of AIIIBV compounds films obtained in the studies described above were used for obtaining of AlGaAs/InGaAs/GaAs multi-layer heterostructures on fianite. These structures were used in FET. Sequential growth AIIIBV heteroepitaxial layers on the fianite substrates was conducted according to topologic scheme of PHEMT (Pseudomorphic High Electron Mobility Transistor) for microwave frequency FET operating in 10-40 GHz range (Tab. 3) using «Aixtron AIX 200RF»installation. Capillary epitaxy MOCVD technique in 550–600С temperature range was used.

Grown by «capillary epitaxy» techniques series of GaSb and GaAs:Sb buffer layers on (111) and (100) fianite substrates were developed to decrease the surface roughness of the PHEMT heterostructure. The buffer layers had a uniform mirror-smooth surface with about 5 nm roughness. Application of the developed buffers made it possible to obtain an AlGaAs/InGaAs/GaAs heterostructures with uniform mirror-smooth surface on fianite substrates and to decrease its roughness by a factor of 10 (to 25 nm). As a result, sufficiently

<sup>Е</sup> ( 1) 82Å a b

Fig. 10. X-ray rocking curve of layer GaSb(111)/fianite(111) (a); rocking curve width FWHM GaSb(111) = 0.23o; photoconductivity of GaSb on fianite substrate (b).

Fig. 11. Interference microscope images of surface (а) and the surface relief (b) of buffer layer

The GaSb layers, as well as InAs/GaSb short-period supperlattices are suitable for the development of IR detectors operating in 2-3 μm range. In our studies they were used as

The results on epitaxial growth of AIIIBV compounds films obtained in the studies described above were used for obtaining of AlGaAs/InGaAs/GaAs multi-layer heterostructures on fianite. These structures were used in FET. Sequential growth AIIIBV heteroepitaxial layers on the fianite substrates was conducted according to topologic scheme of PHEMT (Pseudomorphic High Electron Mobility Transistor) for microwave frequency FET operating in 10-40 GHz range (Tab. 3) using «Aixtron AIX 200RF»installation. Capillary epitaxy

Grown by «capillary epitaxy» techniques series of GaSb and GaAs:Sb buffer layers on (111) and (100) fianite substrates were developed to decrease the surface roughness of the PHEMT heterostructure. The buffer layers had a uniform mirror-smooth surface with about 5 nm roughness. Application of the developed buffers made it possible to obtain an AlGaAs/InGaAs/GaAs heterostructures with uniform mirror-smooth surface on fianite substrates and to decrease its roughness by a factor of 10 (to 25 nm). As a result, sufficiently

**3.3.4 Deposition of GaAs, AlGaAs, InGaAs – Based multilayer structures** 

Z5551 /2 - скан со щелью 0.25 мм. Окрестность пика GaSb(111)

a b

MOCVD technique in 550–600С temperature range was used.

GaAs:Sb on fianite (Interference microscope Talysurf).

buffers for AIIIN growth on fianite substrates.

**on fianite** 

homogeneous AlGaAs/InGaAs/GaAs multi-layer heterostructures with smooth slightly bloom surface were grown on (001) fianite substrates of 50 mm diameter. Roughness of the heterostructure surface measured using Talysurf interference microscope (3-dimensional topography) was 0.25 μm. This structure was grown using «AIXTRON» installation on (100) fianite ellipsoidal substrate of 2 inch major diameter. The surface of multilayer structure is rather uniform but its roughness reaches the value of 25 nm.


Table 3. PHEMT heterostructure for FET operating in 10-40 GHz range

Structural perfection of AlGaAs/InGaAs/GaAs multi-layer heterostructures on fianite was investigated by means of XRD. DRON-4 device (Ge(004) monochromator, CuK1 radiation) was used. /2 - spectra were recorded at symmetric reflection mode by scanning with 0.1 steps of texture maxima rocking. X-ray diffraction /2 - spectrum of GaAs (001) / fianite (001) is shown in Fig. 12. The peaks of (Zr,Y)O2 (004), 2 = 73.4 substrate and of GaAs(004), 2 = 66.05 buffer layer were recorded. The width of the layer rocking curve FWHM = 1 that is the evidence of a mosaic structure of GaAs layer. The grain-boundary angle was ~ 1 (Fig. 12a). Preliminary conditions of the growth of AlGaAs/InGaAs/GaAs heterostructures on fianite has shown that the use of (111) fianite substrate with GaAs:Sb buffer layer allowed reaching of mirror-flat homogeneous surface and 10-fold decrease of its roughness up to 0.025 μm value.

Layer-by-layer SIMS analysis of the heterostructures on fianite was carried out using «Shipovnik 3» and «TOF SIMS-5» devices. These devices provide detailed information on elemental and molecular composition in thin sub-surface layers, as well as 3-dimensional analysis. Sputtering was carried out by Cs+,2 keV, raster 250250 μm, negative ion detection mode, the probe beam Bi+, 25 keV, depth resolution DZ > 7 nm. The analysis of the AlGaAs/InGaAs/GaAs heterostructures obtained on fianite (Fig. 12b) has shown that its inner topology was in conformity with the assigned scheme (Tab. 3) of the PHEMTstructure.

Fianite in Photonics 149

Hydrogen is conventional carrier gas in MOGPE of III-V materials because it is rather readily can be purified. Similarly, in MOGPE of nitrides of III group hydrogen for the first time was used as a carrier gas. However, later it was demonstrated that in contrast to classic III-V semiconductors, GaN and InN are unstable under hydrogen atmosphere and undergo destruction (etching) at the temperatures used for growth of these crystals. This is an evidence that hydrogen as a carrier gas at the epitaxy of nitrides of III group elements actively participates in the process occurring on the surface of growing layer, in contrast to GaAs. Therefore, in most cases for growth of nitrides of III group by MOGPE ammonia is used as nitrogen source and supplied into reactor in large quantities. For a long time ammonium was because that it inhibits the destruction of a growing film and makes the effect of hydrogen negligible. However, it appears that it is far from the case and hydrogen

The studies have shown that at annealing of LT-GaN nucleus layer, the latter undergo etching in H2-NH3 flow hindering growth of a high-quality GaN layer. Application of the low-temperature AlN nucleus layer with annealing in hydrogen-ammonia atmosphere, as well as the high-temperature AlN nucleus layer on (111) and (100) oriented fianite substrates resulted in formation of hexagonal GaN layers comprising a textured polycrystal of hexagonal modification. Scattering angles of the texture for the GaN layers grown on the

It has been shown that the high-temperature annealing of LT-GaN buffer layer at 1000- 1100С promotes improvement of structural perfection GaN heteroepitaxial layer. The GaN layers on fianite substrates exhibited an intense photoluminescence with maximum at

The conditions of growth of single-crystal GaN layers on (111) and (100) fianite substrates by MOCVD without buffer layer at 850oC substrate temperature has been determined. The

Two peaks of the substrate were observed at 30o YSZ(111) and 34.8o YSZ(200). The layer provides a single GaN(0002) peak at 34.5. Since GaN (0002) peak is close to YSZ(200) a narrow slit in front of the detector was inserted with the purpose to increase the resolution. GaNhex (0001) was detected on the both substrates at FWHM < 1 that corresponds to

spectra of /2 scanning were obtained with monochromator Ge(400) (fig. 13).

significantly influenced on the process of the nitrides growth.

(111) and (100) oriented substrates were 10 and 15, respectively.

Fig. 13. XRD spectra of GaN on (111) and (100) fianite substrate.

365 nm.

Fig. 12. X-ray diffraction pattern (a) and layer-by-layer secondary ion mass-spectrometry (b) of the multilayer heterostructure AlGaAs/InGaAs/ GaAs (001) / fianite (001).

#### **3.4 AIIIN films on fianite substrates and buffer layers**

Principal difficulty of growth of perfect heteroepitaxial GaN layers is an absence of suitable substrates having good matching with the heteroepitaxial layer. Currently, for the growth of GaN layers Al2O3, ZnO, MgO, SiC, Si, GaAs substrates are in use. Usually, a material with wurtzite structure is grown on a hexagonal substrate, whereas sphalerite - on a cubic one. Fianite as a substrate material for cubic InGaN epitaxy has a number of advantages, such as favorite crystallochemical parameters and high chemical stability. Besides fianite, Si and GaAs substrates with fianite buffer layer were developed in scope of the work. Synthesis of the layer was carried out by laser deposition technique. The growth of fianite films on silicon substrates was conducted with the purpose to evaluate prospects of the use of less expensive large silicon substrates with fianite sublayer instead of monolithic fianite because maximum dimensions of the silicon-on-fianite structures are limited by size and quality of fianite crystals and the corresponding substrates (currently 50 mm). Another purpose of the study was determination of suitability of fianite not only as a substrate material but also as a gate dielectric. Producing of such substrates will allow integrating GaN-based optoelectronics with a well-developed silicon electronics and gallium arsenide electronics and optoelectronics.

#### **3.4.1 GaN films on fianite substrates**

Growth of the films on (111) and (100) oriented fianite substrates was carried out using nucleus layers. 3 types of the nucleus layers were used:


At the use of all of the types of the nucleus layers fianite substrates were annealed in pure hydrogen at ~10700С before deposition of the nucleus layers.

Fig. 12. X-ray diffraction pattern (a) and layer-by-layer secondary ion mass-spectrometry (b)

Principal difficulty of growth of perfect heteroepitaxial GaN layers is an absence of suitable substrates having good matching with the heteroepitaxial layer. Currently, for the growth of GaN layers Al2O3, ZnO, MgO, SiC, Si, GaAs substrates are in use. Usually, a material with wurtzite structure is grown on a hexagonal substrate, whereas sphalerite - on a cubic one. Fianite as a substrate material for cubic InGaN epitaxy has a number of advantages, such as favorite crystallochemical parameters and high chemical stability. Besides fianite, Si and GaAs substrates with fianite buffer layer were developed in scope of the work. Synthesis of the layer was carried out by laser deposition technique. The growth of fianite films on silicon substrates was conducted with the purpose to evaluate prospects of the use of less expensive large silicon substrates with fianite sublayer instead of monolithic fianite because maximum dimensions of the silicon-on-fianite structures are limited by size and quality of fianite crystals and the corresponding substrates (currently 50 mm). Another purpose of the study was determination of suitability of fianite not only as a substrate material but also as a gate dielectric. Producing of such substrates will allow integrating GaN-based optoelectronics with a well-developed silicon electronics and gallium arsenide electronics

Growth of the films on (111) and (100) oriented fianite substrates was carried out using

1. Low-temperature GaN nucleus layer with annealing in hydrogen-ammonia

2. Low-temperature AlN nucleus layer with annealing in hydrogen-ammonia

At the use of all of the types of the nucleus layers fianite substrates were annealed in pure

a b

**3.4 AIIIN films on fianite substrates and buffer layers** 

and optoelectronics.

atmosphere;

atmosphere;

**3.4.1 GaN films on fianite substrates** 

3. High-temperature AlN nucleus layer.

nucleus layers. 3 types of the nucleus layers were used:

hydrogen at ~10700С before deposition of the nucleus layers.

of the multilayer heterostructure AlGaAs/InGaAs/ GaAs (001) / fianite (001).

Hydrogen is conventional carrier gas in MOGPE of III-V materials because it is rather readily can be purified. Similarly, in MOGPE of nitrides of III group hydrogen for the first time was used as a carrier gas. However, later it was demonstrated that in contrast to classic III-V semiconductors, GaN and InN are unstable under hydrogen atmosphere and undergo destruction (etching) at the temperatures used for growth of these crystals. This is an evidence that hydrogen as a carrier gas at the epitaxy of nitrides of III group elements actively participates in the process occurring on the surface of growing layer, in contrast to GaAs. Therefore, in most cases for growth of nitrides of III group by MOGPE ammonia is used as nitrogen source and supplied into reactor in large quantities. For a long time ammonium was because that it inhibits the destruction of a growing film and makes the effect of hydrogen negligible. However, it appears that it is far from the case and hydrogen significantly influenced on the process of the nitrides growth.

The studies have shown that at annealing of LT-GaN nucleus layer, the latter undergo etching in H2 -NH3 flow hindering growth of a high-quality GaN layer. Application of the low-temperature AlN nucleus layer with annealing in hydrogen-ammonia atmosphere, as well as the high-temperature AlN nucleus layer on (111) and (100) oriented fianite substrates resulted in formation of hexagonal GaN layers comprising a textured polycrystal of hexagonal modification. Scattering angles of the texture for the GaN layers grown on the (111) and (100) oriented substrates were 10 and 15, respectively.

It has been shown that the high-temperature annealing of LT-GaN buffer layer at 1000- 1100С promotes improvement of structural perfection GaN heteroepitaxial layer. The GaN layers on fianite substrates exhibited an intense photoluminescence with maximum at 365 nm.

The conditions of growth of single-crystal GaN layers on (111) and (100) fianite substrates by MOCVD without buffer layer at 850oC substrate temperature has been determined. The spectra of /2 scanning were obtained with monochromator Ge(400) (fig. 13).

Fig. 13. XRD spectra of GaN on (111) and (100) fianite substrate.

Two peaks of the substrate were observed at 30o YSZ(111) and 34.8o YSZ(200). The layer provides a single GaN(0002) peak at 34.5. Since GaN (0002) peak is close to YSZ(200) a narrow slit in front of the detector was inserted with the purpose to increase the resolution. GaNhex (0001) was detected on the both substrates at FWHM < 1 that corresponds to

Fianite in Photonics 151

The study has shown that the layers had uniform distribution of its constituents, the concentration profile of Zr atoms at the hetero-interface being very sharp (Fig. 14c). The use of AlN nucleating layers on the fianite buffering layers allows deposition of continuous and

Comparative study of density and electric activity of structural defects in the GaN epitaxial films grown on GaAs substrates with various buffer layers were carried out by **Induced bias technique**. Induced bias (IBT) technique has been developed rather recently [30, 31]. It is contact-free similarity of induced current technique (EBICmode). IBT is nondestructive contact-free diagnostic technique of semiconducting materials and microelectronic devices. IBT is based on detecting of voltage (or charge) generated by an electron probe of scanning electron microscope (SEM). Draft-scheme is

a b c

Fig. 15. Outline of induced potential method (a) and scanning electron microscope images of electrically active polygonal defects in GaAs films: secondary-electron emission mode (b);

The electron probe (e) scans the surface of a crystal under the study (O). Metal ring (D), in which surface charge generated by electrons through capacitive coupling is induced, is a detector of the signal. The signal from the ring electrode is monitored in the SEM display (or by other measurement equipment) through charge-sensitive amplifier (PA) (Fig. 15 a). The technique allows qualitative monitoring of semiconductor plates, structures and devices identifying electric active inhomogeneities such as dislocations, stacking faults, microfractures, extent of doping by various dopants, all *p-n* junctions and Schottky barriers, etc (see for example Fig. 15 b,c). Quantitative measurements of local fundamental characteristics of semiconductors are also possible (diffusion distance, nonequilibrium carrier lifetime, its

The studies have shown that the use of GaAs substrates with porous GaAs layer resulted in a decrease of the electric activity of structural defects in the GaN films and in an increase of its electrical uniformity as compared to GaN films grown on monolithic GaAs substrates. The use of GaAs substrates with double buffer layer (fianite on porous GaAs) allows additionally decreasing concentration of the electrically active defects in the GaN films to

**3.4.3 Electrically active defects in GaN films on GaAs substrates with fianite** 

homogeneous GaN layers of hexagonal modification.

**buffer layers** 

shown in Fig. 15 a.

b - induced potential mode (c).

surface recombination rate, diffusion barrier height).

more than an order of magnitude (Fig. 16).

epitaxial growth. Traces of the polycrystalline phase at 32.4 (suggested 0.1-1.0 intensity units) were not detected.
