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The initial growth of CdTe having a thickness of 20–500 nm on (2 1 1) Si substrates was investigated to observe the growth of CdTe at the interface for hetero-epitaxial growth. The dependence of surface morphologies at the initial growth on the II/VI and the growth time was evaluated. The (1 3 3) surface orientation at the interface was shown in CdTe films grown on (2 1 1) Si substrates, which was irrespective of the II/VI. For a relatively high II/VI of 36, hillocks having a (2 1 1) orientation were observed on the underlayer having a (1 3 3) orientation. CdTe having a (2 1 1) orientation was dominant during the growth, due to its lateral coalescence on the underlayer. The dependence of the orientation between (1 3 3) and (2 1 1) CdTe films on (2 1 1) Si substrates on the II/VI was explained by the difference between the step-flow growth on the step and the spontaneous nucleation on the terrace.

In this paper, we investigated the effects of the growth temperature and chlorine gas on the growth of thick GaN on an N-polar GaN substrate via tri-halide vapor phase epitaxy. The results revealed that free Cl2 is necessary for high-speed growth. When the growth temperature increases, the crystal quality improves, and a high growth rate and high crystalline quality can be simultaneously achieved.

Single-crystalline CdTe films were grown in both (133) and (211) surface orientations on (211) Si substrates by vapor-phase epitaxy using metallic Cd source as a group-II precursor. The orientation of epitaxial films depended on the ratio of group-II and -VI precursors, i.e., II/VI. The orientation of epitaxial films was changed from (133) to (211) by increasing the II/VI under the CdTe growth condition. The surface morphology for (133) CdTe was smooth, whereas the surface for (211) CdTe was composed of hillocks with (111), (110), (101), and (100) facets. The full width at half maximum (FWHM) of the epitaxial films with the same thickness showed that the crystalline quality of (133) CdTe was better than that of (211) CdTe. The dependence of the orientation between (133) and (211) CdTe films on (211) Si substrates on the II/VI was explained by the difference between the step-flow growth on the step and the spontaneous nucleation on the terrace.

We successfully performed epitaxial CdTe growth on a Si (211) substrate with vapor-phase epitaxy using a cost-effective metallic cadmium source as a group-II precursor. The thermodynamic data demonstrate that the combination of metallic Cd and diisopropyl-telluride (DiPTe) with a H2 carrier gas enables the growth of CdTe crystals. A CdTe single crystal with a (422) surface orientation was obtained when a growth temperature between 600°C and 650°C was employed. The surface morphology and crystalline quality were improved with increasing film thickness. The full-width at half-maximum of the x-ray rocking curves with a film thickness of 15.7 μm for the skew-symmetrical (422) and asymmetrical (111) reflection were 528 arcsec and 615 arcsec, respectively.

GaN layers of thickness 0.5–1.3 mm were grown at 1280 °C at a growth rate of 95–275 µm/h by tri-halide vapor-phase epitaxy on nonpolar m -plane ( 10 1 0 ) and semipolar ( 10 1 1 ) ammonothermal GaN substrates. For nonpolar m -plane ( 10 1 0 ) with a −5° off-angle, the full widths at half maximum (FWHMs) of X-ray rocking curves (XRCs) and the basal plane stacking fault (BSF) density increased from 50 to 178″ and from 4.8×10 1 to 1.0×10 3 cm −1 , respectively, upon increasing the growth rate from 115 to 245 µm/h. On the other hand, the XRC-FWHM and the BSF density for semipolar ( 10 1 1 ) grown at 275 µm/h were as small as 28″ and 8.3×10 1 cm −1 , respectively.

The dependence of growth temperature for the epitaxial films grown by tri-halide vapor phase epitaxy (THVPE) on the crystal characteristics, such as the surface morphology, the full width at half maximum (FWHM), the threading dislocation density (TDD), the impurity concentration, and the photoluminescence (PL) was investigated. The epitaxial films grown at relatively high growth temperature of 1300-1350 °C showed that the crystal quality, such as FWHM and TDD retained that for the used substrate. The near-band-edge emission for PL for 1300-1350 °C growth showed lager intensities due to low nonradiative recombination center (NRC). Moreover, the epitaxial growth on the supercritical acidic ammonia technology (SCAAT™) substrate was demonstrated. The TDD was as low as 2 × 104 cm-2, which indicated that the epilayer grown by THVPE retained the superior crystal quality of SCAAT™.

Tri-halide vapor phase epitaxy (THVPE) of thick GaN using GaCl3 was investigated for fabricating low-cost, high-crystalline-quality GaN substrates instead of the conventional manufacturing method of GaCl-based hydride vapor phase epitaxy (HVPE). The growth rate and upper growth temperature limit of GaN using THVPE were found to be much higher than those obtained using conventional HVPE under the same growth conditions. Drastic reduction in the number of dark spots measured by cathodoluminescence at room temperature was observed for the high-temperature-grown GaN layer on the (000-1) GaN/sapphire template due to the enhancement of precursor migration on the growing surface. It was found that the incorporation of impurities such as O, C, and Cl can be reduced even on the N-polarity GaN by increasing the growth temperature. The possibility of enlargement of the crystal diameter by growing the N-polarity GaN layer using THVPE was also proposed.

Deep-level luminescence at 3.3 eV related to the presence of Al vacancies (V Al ) was observed in room temperature photoluminescence (RT-PL) spectra of homoepitaxial AlN layers grown at 1450 °C by hydride vapor-phase epitaxy (HVPE) and cooled to RT in a mixture of H 2 and N 2 with added NH 3 . However, this luminescence disappeared after removing the near surface layer of AlN by polishing. In addition, the deep-level luminescence was not observed when the post-growth cooling of AlN was conducted without NH 3 . Secondary ion mass spectrometry (SIMS) studies revealed that although the point defect density of the interior of the AlN layers remained low, the near surface layer cooled in the presence of NH 3 was contaminated by Si impurities due to both suppression of the surface decomposition by the added NH 3 and volatilization of Si by decomposition of the quartz reactor walls at high temperatures. The deep-level luminescence reappeared after the polished AlN wafers were heated in presence of NH 3 at temperatures above 1400 °C. The surface contamination by Si is thought to generate V Al near the surface by lowering their formation energy due to the Fermi level effect, resulting in deep-level luminescence at 3.3 eV caused by the shallow donor (Si) to V Al transition.

A thick and fully relaxed In0.05Ga0.95N layer was epitaxially grown on a GaN substrate after growing partially relaxed intermediate InGaN layers using tri-halide vapor phase epitaxy. In order to control the relaxation ratio of intermediate InGaN layers, a double intermediate structure with different growth rates (low growth rate and high growth rate modes) was adopted. By changing the first intermediate InGaN layer thickness, the relaxation ratio could be varied in the ranges between 25% and 59%. According to X-ray diffraction reciprocal space mapping measurements, a fully relaxed In0.05Ga0.95N layer was successfully grown on a partially relaxed intermediate In0.10Ga0.90N layer with the relaxation ratio of 32%. Thus, a mirror-like, fully relaxed and thick In0.05Ga0.95N layer could be grown with lattice matched to the intermediate InGaN layers by controlling the relaxation ratio.

GaN with a film thickness of 200–600 μm was grown on the as-grown three-dimensional supercritical acidic ammonia technology (SCAATTM) bulk seed that comprised only semipolar { 10 1 ¯ 1 ¯ } planes at a temperature as high as 1390 °C by tri-halide vapor phase epitaxy; further, the GaN film was also characterized. The FWHM value of the X-ray rocking curves was ∼40″, which was almost similar to the value of the used seed. The curvature radii were as large as 40–64 m. Further, the carrier concentrations were observed to be as small as 5.1 × 1017–9.1 × 1017 cm−3. However, the basal plane stacking fault densities were observed to be 3.4 × 101–5.4 × 101 cm−1 and were observed to increase during the growth process because of the as-grown SCAATTM seed surface condition.

In this report, effects of ammonia nitridation and low temperature InN buffer growth were investigated to improve the crystalline quality of InN(101¯3) grown on GaAs(110) by metalorganic vapor phase epitaxy (MOVPE). InN(101¯3) single crystal including less than 0.1% of differently oriented domains was successfully grown by inserting low temperature InN buffer layer. The full width at half maximum (FWHM) values of InN(101¯3) epitaxial layer were drastically decreased from 89 arcmin to 55 arcmin after processing ammonia nitridation of GaAs(110) substrate surface. Furthermore, the FWHM value was decreased to 38 arcmin by increasing growth time, and the mechanism of dislocation annihilation happened during epitaxial growth was discussed.

Thermodynamic analyses on hydride vapor phase epitaxy (HVPE) of InGaN using III-chlorides, III-bromides, and III-iodides were performed to search a promising source material having a potential for controlling the solid composition with a high growth rate. In this analysis, various precursors such as InCl3, GaCl3,InBr3, GaBr3, InI3, and GaI3 were selected for comparison. Influence of input mole fraction of hydrogen (H2) in the carrier gas and input V/III ratio on the equilibrium partial pressures at InGaN deposition zone and the driving forces of InGaN deposition are shown. It was found that HVPE growth of InGaN using a combination of InCl3 and GaCl3 under a low input mole fraction of H2 and a high V/III ratio is essential for the control of solid composition and for high growth rate. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of hydrogen (H2) in the carrier gas on the crystalline quality as well as twin-crystal formation were investigated in the metalorganic vapor phase epitaxy (MOVPE) of InN on GaAs(110). The inclusion of twin crystals of InN(10-13) was suppressed by the introduction of a small amount of H2 during crystal growth. The surface morphology of the InN layer was also significantly influenced by the input partial pressure of H2 in the carrier gas. The suppression of twin-crystal formation and improvements in the surface morphology can be explained by the differences in the stability of the In- and N-polar InN{0001} asymmetric planes in the presence of H2. Both electronic and optical properties were improved by the introduction of H2, which was probably due to the reduction of impurities such as oxygen and carbon in the InN grown layer. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Heat treatment of (0001) sapphire substrates in the temperature range 980–1480 °C was investigated in an atmospheric-pressure mixed flow of H2 and N2 for various molar fractions of H2 (F°=H2/(H2+N2)). At 1330 °C, AlN whiskers formed on the sapphire surfaces only when the heat treatment was performed in the presence of both H2 and N2 (0

In this paper, we use thermodynamic analysis to determine how the nitrogen (N) ratio in the source gases affects the solid composition of coherently grown GaAs 1− x N x ( x ∼0.03). The source gases for Ga, As, and N are trimethylgallium ((CH 3 ) 3 Ga), arsine (AsH 3 ), and ammonia (NH 3 ), respectively. The growth occurs on a Ge substrate, and the analysis includes the stress from the substrate–crystal lattice mismatch. Calculation results indicate that to have just a few percent N incorporation into the grown solid, the V/III ratio in the source gases should be several thousands and the input-gas partial-pressure ratio NH 3 /(NH 3 +AsH 3 ) should exceed 0.99. We also find that the lattice mismatch stress from the Ge substrate increases the V/III source–gas ratio required for stable growth, whereas an increase in input Ga partial pressure ratio has the opposite effect.

The adsorption processes of group-V sources used in metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) were investigated using first-principle calculations based on the density functional theory (DFT) to understand the initial growth process of AlN(0001). To examine the influence of surface hydrogen coverage on the initial growth process, the ideal surface and a reconstructed surface with an adsorbed 0.75 monolayer of hydrogen were used as the initial surface structures. NH3 and NH2 generated by the decomposition of NH3 were considered as group-V sources. From the calculations, the influence of surface hydrogen coverage on the initial growth process of AlN(0001) surfaces in vapor phase epitaxy was clarified. It was revealed that surface hydrogen coverage does not have an effect on adsorption of NH3, whereas NH2 was affected by hydrogen on the surface. It was also demonstrated that the adsorption energies for NH3 and NH2 on the ideal and reconstructed GaN(0001) surfaces are smaller than those on the ideal and reconstructed AlN(0001) surfaces (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of InGaN alloy using hydride vapor phase epitaxy (HVPE) was investigated. Thermodynamic analysis was performed, taking account of the source zones. It was found that InCl 3 and GaCl 3 , which are known to be essential for appreciable InGaN growth by HVPE, could be generated preferentially at the source zone by using a group-III metal and Cl 2 gas. The analysis for the growth zone revealed that a significantly large driving force for both InN and GaN deposition is possible. The calculated vapor–solid distribution was close to a linear relationship by using a high V/III ratio, inert carrier gas, and high temperature. These facts suggest that an InGaN thick layer can be grown with a high growth rate and enough controllability of solid composition by employing InCl 3 and GaCl 3 precursors.

Investigation of the hetero-epitaxial growth of InN on a GaAs (1 1 0) substrate was performed by metalorganic vapor phase epitaxy in order to realize the formation of semi-polar InN layer on it. The orientation relationship between InN and GaAs (1 1 0) was confirmed by 2θ―ω and pole figure of X-ray diffraction measurements. It was found that the crystalline orientation strongly depended on the growth temperature; mixed domains of (1 0 1 3) and (1 1 2 0) InN have been grown on GaAs (1 1 0) surfaces when the growth temperature was below 550 °C, while (1 0 1 3) semi-polar InN layers could be grown by increasing the growth temperature above 575 °C. It was also found that the in-plane anisotropy of semipolar InN layer was suppressed by increasing the growth temperature. Epitaxial relationship of the InN with the GaAs (1 1 0) substrate was InN (1 0 1 3) plane parallel to GaAs (1 1 0) and InN (2 1 1 0) plane parallel to GaAs(1 1 0).

Thermodynamic analyses of halide vapor phase epitaxy (HVPE) for the growth of ZnO were conducted to investigate the effects of growth conditions against growth rates. The partial pressures of gaseous species in equilibrium with ZnO and the resultant driving force for ZnO deposition are calculated with respect to temperatures, input H 2 pressures and input VI/II ratios. It has been revealed that the driving force is weakly dependent on the temperature and is still positive even at 1200 °C, while it greatly decreases at higher temperatures in the presence of H 2 . The driving force is also significantly influenced when the VI/II ratio is below 1000. The experimental growth rates substantially agree with the dispositions of the driving force expected from the thermodynamic analyses.

The surface morphology of homoepitaxial (0 0 0 1)ZnO thin layers grown by halide vapor phase epitaxy (HVPE) using ZnCl2 and H2O source gases was investigated. Atomic force microscopy (AFM) observations showed that high temperature growth at 1000 °C with a low input H2O/ZnCl2 (VI/II) partial pressure ratio of 20 strongly promoted step-flow growth. X-ray diffraction (XRD) analyses revealed the crystalline quality of the homoepitaxial ZnO layer grown at 1000 °C with input VI/II ratio of 20 is comparable to that of bulk ZnO substrates. Under a constant input partial pressure of ZnCl2, the growth rate of ZnO is constant within the temperature range 700–900 °C, and the growth rate decreases above 900 °C due to the shift of thermodynamic equilibrium of the growth reaction.

InN layers were grown on both-sides-polished (0 0 0 1) freestanding GaN substrates by hydride vapor-phase epitaxy (HVPE) in the growth temperature range from 450 to 650 °C with an input partial pressure of NH 3 ranging from 3.0×10 −2 to 3.8×10 −1 atm. An In-polar InN layer was grown on the (0 0 0 1) Ga-polar surface, while a N-polar InN layer was grown on the (0 0 0 1 ¯ ) N-polar surface of the freestanding GaN substrate. The InN layers of both polarities grown at 550 °C had smooth surfaces, ideal lattice constants of the wurtzite InN structure, and a minimum optical absorption edge energy of about 0.75 eV. Surface morphologies of the InN layers were also dependent on the NH 3 input partial pressure. The surface of In-polar InN became smoother under a high NH 3 input partial pressure, whereas the N-polar InN required a low NH 3 input partial pressure to achieve a smooth surface.

Facet control of InN was performed for the improvement of the crystalline quality of InN layers on GaAs (1 1 1)B by metalorganic vapor phase epitaxy (MOVPE). Growth mode of InN could be controlled by changing the input mole ratio of hydrogen in the carrier gas and growth temperature. When the input mole ratio of hydrogen in the carrier gas was 0 (N 2 ambient) and growth temperature was low, InN with a flat surface could be obtained. On the contrary, when a small amount of hydrogen was contained in the carrier gas (0.4% of H 2 ), InN islands having a (1 0 1¯ 2) facet were grown. It was also found that the crystalline quality of InN could be improved by employing a growth mode change during epitaxial growth from three dimensional (3D) to two dimensional (2D), indicating a reduction in dislocation density.

MnP nanowires have been grown by molecular beam epitaxy (MBE) without any preliminary deposited metal catalyst on InP(100) and GaAs(111)B substrates. Mn was supplied using a conventional Knudsen cell, whereas P2 was supplied as a gas by the decomposition of tertiary butylphosphine (TBP) using a cracking cell. The self-assembled growth of nanowires was observed when the substrate temperature exceeded 430 °C. Nanowires obtained on the InP(100) surface had diameters close to 150 nm, lengths of up to 2 µm, whereas nanowires grown on the GaAs(111)B surface had widths of up to 600 nm, lengths of up to 30 µm, and clear atomic facets. Magnetic and optical characterizations were also carried out.

High-temperature growth of thick AlN layers was performed by solid source halide vapor-phase epitaxy (HVPE) with local heating system. It was found that crystalline quality of AlN layers grown on sapphire (0 0 0 1) substrates improved with increase of growth temperature until 1500 °C. Degradation of crystalline quality occurred over 1550 °C, which is thought to be due to the decomposition of AlN crystal or sapphire substrate during the epitaxial growth. The full-width at half-maximum (FWHM) values of (0 0 0 2) and ( 1 0 1 ¯ 0 ) diffraction from the AlN layer grown at 1500 °C were 103 and 828 arcsec, respectively. Secondary ion mass spectrometry (SIMS) measurement showed a high concentration of oxygen incorporated into the AlN layer through the interface between sapphire and AlN at 1550 °C. The near band-edge emission peaking at 208.2 nm was also observed by cathodoluminescence measurement at room temperature.

The thermal stability and reaction with H2 of the surface of a (1012) R-plane sapphire substrate at high temperatures were investigated using an in situ gravimetric monitoring system. Although the R-plane sapphire surface was stable up to 1400 °C in an inert carrier gas, decomposition started at 1200 °C in H2 carrier gas. In addition, the activation energy for the decomposition of R-plane sapphire in H2 carrier gas changed at approximately 1300 °C, which indicates that the rate-limiting reaction for the decomposition of the R-plane sapphire substrate shifts near 1300 °C. These results agree with those for the stability of the C-plane sapphire substrate, as described previously. However, it was found that decomposition rate of the R-plane sapphire substrate was significantly greater than that for the C-plane substrate. The relationship between the decomposition rate and the surface orientation of sapphire and detailed mechanisms for the decomposition of R- and C-plane sapphire in H2 carrier gas are discussed.

N-polarity InN layers grown on (0001) sapphire substrates by hydride vapor phase epitaxy (HVPE) were annealed in atmospheric N2, H2, H2 + NH3, or N2 + NH3 ambient at various temperatures. In the N2 ambient, InN decomposition became significant above 600 °C, whereas in the H2 ambient, InN layers reacted with H2 and decomposed at very low temperatures above 350 °C. The process of InN decomposition was also investigated using a first-principles calculation. In a system free from H2, the rate-limiting process was found to be desorption of N atoms from the surface as atomic N (N*), whereas in the H2 ambient, the desorption of In atoms as In, InH or InH3 is the rate-limiting process. Thus, the decomposition reactions of InN layers in the ambient in the presence and absence of H2 are different. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Influences of hydrogen input partial pressure in the carrier gas ( F o = P H 2 o / ( P H 2 o + P N 2 o ) ) on the crystalline quality and polarities of InN on GaAs (1 1 1)A surfaces were investigated by metalorganic vapor phase epitaxy (MOVPE). It was found that the polarity of the InN was affected by the hydrogen gas in the system regardless of the polarity of GaAs starting substrate. The polarity of InN layer grown with the hydrogen partial pressure of F o =0.004 was a mixture of In-polarity and N-polarity, while that grown with F o =0 was In-polarity. Degradation of the crystalline quality of InN grown with F o =0.004 occurred due to the polarity inversion during the growth. The reason why the polarity of InN was influenced by the hydrogen carrier gas could be explained by the preferential growth of N-polarity InN in the H 2 contained ambient and/or the limiting reaction of InN decomposition.

Secondary-ion mass spectroscopic studies for wurtzite GaN (0 0 0 1) and ( 0 0 0 1 ¯ ) surfaces grown by hydride-vapor phase epitaxy were carried out using highly-charged ions. The secondary ions of impurities adsorbed on the surfaces, such as proton, H 2 + , and C m H n + ( m = 1–6 and n = 0–13), were preferentially desorbed by the grazing incidence of Ar q + ( q = 6–11). A spectrum peak of Ga + was observed only in the (0 0 0 1) surface, whereas an enhancement of the peak intensity of N + was observed in the ( 0 0 0 1 ¯ ) surfaces. The time difference between the two peaks was also observed in the time-of-flight spectra of protons emitted from the (0 0 0 1) and ( 0 0 0 1 ¯ ) surfaces. It was concluded that these differences were due to the surface polarity of GaN.

We report the growth of N- and Al-polar AlN layers on c-plane sapphire by flow-modulation MOCVD (FM-MOCVD) with some flow sequence modifications. Surface polarities were decided by pre-treatment for sapphire substrates prior to AlN seeding layer growth. Low-temperature nitridation (620 °C) was done for the N-polar samples, and no-nitridation was done for the Al-polar. To avoid strong vapor-phase reaction between TMA and NH 3 and to enhance the surface migration of Al atoms, FM-MOCVD technique was used. The flow sequence was modified for optimization of each N- and Al-polar growth. The surface features were completely different between the N- and Al-polar AlN layers in atomic force microscope images. The former had domed structures and the latter atomic steps. The dislocation densities were counted from plane-view transmission microscope images to be about 3 x 10 10 cm -2 for the N-polar layer and about 1×10 10 cm -2 for the Al-polar. Secondary-ion mass spectroscopy measurement revealed oxygen- and carbon-incorporation into the layers. Band-edge and impurity-related emissions were observed from only the Al-polar layer by room-temperature cathodoluminescence, whereas the N-polar one did not emit.

The thermal stabilities of Al- and N-polarity AlN layers grown on (0 0 0 1) sapphire substrates were investigated at temperatures ranging from 1100 to 1400 °C in various gas flows (He, H 2 and H 2 +NH 3 ). Decomposition of AlN occurred in flowing H 2 , while it did not occur in He or H 2 +NH 3 flow. The decomposition rate in H 2 increased with an increase in the temperature over 1200 °C, and the decomposition rate of the Al-polarity AlN layer was found to be lower than that of the N-polarity AlN layer at each temperature. The decomposition reaction of AlN and the relationship between the polarities of the AlN layers and their different decomposition rates are discussed.

We have demonstrated that high-quality aluminium nintride (AlN) single crystal can be grown at high growth rates by hydride vapor phase epitaxy (HVPE) with a help of using AlN templates and step growth technique. A colorless and transparent AlN layer with 83 μm thick was grown at a growth rate of 57 μm/h at 1450 °C. Its full-width at half-maximum for {0 0 0 2} plane was 295 arcsec and that for {1 0 1¯ 1} plane was 432 arcsec. Grown AlN layer was transparent in the visible and ultraviolet region and a sharp absorption edge with band gap energy of 5.96 eV was confined.

HVPE growth of AlGaN ternary alloy using AlCl 3 -GaCl-NH 3 system is reported. AlGaN alloy was grown directly on sapphire without any buffer layers. It was found that the solid composition could be controlled in all ranges from GaN to A1N by changing the input ratio of the group III precursors under the low partial pressure of H 2 (

A new system for hydride vapor phase epitaxy (HVPE) of thick InN layers using Cl2 was investigated. Thermodynamic analysis was performed for the reactions at the source and the growth zones. It was found that InCl3 can be generated preferentially at the second source zone by adding Cl2 to InCl from the first source zone. The analysis for the growth zone showed that a significantly large driving force for InN deposition is expected. It was shown that the growth of thick InN layers is possible by employing the new HVPE system. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In order to fabricate an Fe-doped semi-insulating (SI) GaN substrate by hydride vapor phase epitaxy (HVPE) using (111)A GaAs as a starting substrate, the Fe doping mechanism was investigated by two approaches: first-principles calculation and X-ray absorption fine structure (XAFS) measurements. First-principles study clarified that Fe and As atoms are substituting for the Ga and N atoms in the wurtzite GaN lattice, respectively. In addition, incorporation of Fe in GaN was found to be hindered by adjacent As in the N site. XAFS analysis performed for an Fe-doped SI GaN substrate, obtained by protecting backside of the GaAs substrate, showed that the Fe atoms are substituting for the Ga site in GaN. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The thermal stability of (0001) sapphire was investigated at atmospheric pressure using the in situ gravimetric monitoring (GM) method. The weight change of a sapphire substrate was monitored at various hydrogen partial pressures in carrier gas (P) at temperatures over 1200 °C. Although the sapphire substrate was stable up to 1450 °C in an inert carrier gas (P = 0.0 atm), sapphire decomposition started to occur at 1200 °C in H2 carrier gas (P = 1.0 atm). Moreover the activation energy and order of reaction for sapphire surface decomposition changed at approximately 1300 °C. These results indicate that the rate-limiting reaction for sapphire decomposition shifts near 1300 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of hydrogen coverage on a Si(1 1 1) substrate on the initial growth of a GaN buffer layer was investigated using Ga and Al adsorption energies obtained by ab initio calculations. It was found that absolute values of the adsorption energies of Ga and Al atoms increased as the hydrogen coverage on the substrate surface decreased. Moreover, it was found that the absolute value of Al adsorption energy was larger than that of Ga in any case. These results suggest that it is important to control the substrate surface condition and carrier gas for the growth of a GaN buffer layer on a Si substrate, though an AlN buffer layer can be grown even under H 2 ambient.

Growth of thick Al x Ga 1− x N ternary alloy using AlCl 3 and GaCl gases as group III precursors was performed by hydride vapor-phase epitaxy (HVPE). C -axis-oriented AlGaN layers could be grown at 1100 °C. It was found that the growth of Al x Ga 1− x N by HVPE was affected by the presence of H 2 in the carrier gas. Therefore, the solid composition x in Al x Ga 1− x N ternary alloy could be controlled by changing the input Al mole ratio of the group III precursor ( R Al ) and/or the low range ( 2 ) in the carrier gas ( F o ). The growth rate of approximately 30 μm/h was obtained under inert carrier gas ( F o =0.0), while the growth rate decreased rapidly in the low R Al under a low partial pressure of H 2 in the carrier gas ( F o =0.1). These results are in good agreement with the thermodynamic prospect. Thus, the growth of Al x Ga 1− x N using HVPE is thermodynamically controlled.

Hydride vapor phase epitaxy (HVPE) of InN using In metal, Cl 2 and NH 3 as source materials and N 2 carrier gas was investigated on sapphire (0001) substrates. A thermodynamic analysis of the reaction between In metal and Cl 2 gas in the source zone of the HVPE system revealed that the equilibrium partial pressure of InCl 3 increased significantly with decreasing source zone temperature, while that of InCI remained almost constant. At a substrate temperature of 500 °C, appreciable growth of InN occurred by decreasing the source zone temperature to 450 °C. This means that InN growth occurs by the reaction between InCl 3 and NH 3 . With an optimum surface nitridation time of the sapphire substrate prior to InN growth, c-axis oriented single-crystalline layers of InN were obtained. Cathodoluminescence (CL) spectrum measured at room temperature showed a strong peak at 0.75eV.

The growth of N-polar AlN layers on c -plane sapphire is reported. Low-temperature AlN (LT-AlN) layers were used as seeding buffer layers with pre-nitridation for sapphire. To avoid strong vapor-phase reaction between trimethylaluminum (TMA) and ammonia (NH 3 ) and to improve the crystalline quality, low-pressure flow-modulated (FM) metal-organic chemical vapor deposition (MOCVD) technique was introduced with careful optimization of the FM sequence. The surface morphologies and the crystalline quality defined by the X-ray diffraction (XRD) (0 0 2) and (1 0 0) rocking curve measurements strongly depended on the LT-AlN thickness and on the TMA coverage per cycle of the FM growth. The sample showing the best XRD data with a good morphology was almost completely etched in aqueous KOH solution owing to N-polarity. From the plan-view transmission electron microscopy (TEM) observation, the dislocation density was counted to be about 3×10 10 cm −2 .

A new MOVPE-like hydride vapor-phase epitaxy (HVPE) using AlCl 3 solid source is proposed for growing thick and high-quality AlN layers. For the new system, a high-purity AlCl 3 (5 N grade) powder was produced. AlN epitaxial layers were characterized by X-ray diffraction (XRD) and optical absorption measurement. Also, impurities such as oxygen and carbon in the epitaxial layer were analyzed comparing to the conventional HVPE system using Al metal and HCl gas. It is shown that the new HVPE system can be applied to mass production, because the Al-precursor can be transported to the reactor as vapor.

An Fe-doped thick GaN layer was grown by hydride vapor-phase epitaxy on a (1 1 1)A GaAs starting substrate. By removing the GaAs substrate, a 400-μm-thick (0 0 0 1) GaN substrate having a smooth surface and an Fe concentration of 1.5×10 19 cm −3 was obtained. X-ray diffraction rocking curves of the (0 0 0 2) and (1 0 1 ¯ 0) planes of the GaN substrate had narrow full-widths at half-maximum of 410 and 360 arcsec, respectively. The etch-pit density of the GaN substrate was 8×10 6 cm −2 . Extended X-ray absorption fine structure analysis revealed that the Fe atoms are substituting for the Ga in the GaN. The GaN substrate had a high resistivity of 8.8×10 12 Ω cm at room temperature.

Thermodynamic study for the hydride vapor phase epitaxy (HVPE) of Alx Ga1–xN was performed to realize the thick, large size AlGaN wafers. It was found that the hydrogen (H2) in the carrier gas affected the resulting solid composition of the alloy. The solid composition x in Alx Ga1–xN can be controlled by changing the H2 mole fraction in the carrier gas. These facts would be explained by difference in the growth reactions between AlN and GaN. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The direct growth of a GaN epitaxial layer on a Si(111) substrate by metalorganic vapor phase epitaxy (MOVPE) was performed using a low-temperature (LT)-GaN buffer layer with no Al-containing intermediate layer (e.g., AlN or AlGaN). No deterioration in the Si surface caused by the reaction between Si and Ga vapor was observed. However, when there were Ga droplets on the surface, Ga and Si formed a Ga?Si alloy, which caused the generation of numerous holes on the surface by melt-back etching at high temperatures. In addition, it was revealed that the coverage of the LT-GaN buffer layer on Si was strongly affected by the hydrogen (H2) partial pressure in the carrier gas. Using nitrogen (N2) carrier gas, a complete coverage of the LT-GaN buffer layer could be achieved directly over the Si surface. These features can be explained by the facts that the Si surface is partially terminated by hydrogen atoms and the coverage of hydrogen on Si surface depends on H2 partial pressure.

We used positron annihilation spectroscopy to study bulk AlN single crystals grown by physical vapor transport (PVT) and hydride vapor phase epitaxy (HVPE). Unlike in previous measurements in AlN, we see a clear Alvacancy related lifetime component already at room temperature in HVPE-AlN. Overall, our results show the more UV-transparent HVPE-AlN to have higher concentration of Al-vacancy related defects than PVT-AlN, suggesting that Al-vacancies are not the origin of UV absorption in AlN. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Novel ternary Mn-containing compound MnGeP2 has been grown on GaAs and InP substrates using molecular beam epitaxy, in which Mn and Ge were supplied from solid sources and P from a gas source. The films obtained showed XRD pattern characteristic of MnGeP2. Lattice constants were determined using reciprocal lattice mapping analysis. Films directly grown on GaAs substrate showed three-dimensional grain-growth. By

A thermodynamic analysis of the hydride vapor phase epitaxy (HVPE) of AlGaN using AlCl 3 and GaCl as group III precursors is described. For a range of values on the input ratio, temperature, and the partial pressure of hydrogen in the carrier gas, we calculated the equilibrium partial pressures and the driving force for A1N and GaN deposition in AlGaN. As a result, we show that controllable AlGaN HVPE is possible under a low partial pressure of hydrogen (

Growth of AlN on sapphire (0 0 0 1) substrates by hydride vapor-phase epitaxy (HVPE) was investigated using AlCl3 and NH3 as source gases in the temperature range from 950 to 1100 °C. It was found that the full-width at half-maximum (FWHM) values of the X-ray diffraction (XRD) rocking curves of the (0 0 0 2) and ( 1 0 1 ¯ 0 ) planes of the c-axis oriented AlN layers decreased with increasing growth temperature. An AlN layer showing a mirror-like surface could be grown at 1100 °C with a growth rate of 1.7 μm/h. Growth rate was found to increase with increasing AlCl3 input partial pressure and with decreasing distance (L) between the end of the AlCl3 injection nozzle and the sapphire substrate. The growth rate reached 122 μm/h with an AlCl3 input partial pressure of 2.0×10−3 atm and L = 25 mm but the crystalline quality became poor when the growth rate rose above 10 μm/h.

Thick Fe-doped GaN layers were grown by metalorganic hydrogen chloride vapor phase epitaxy (MOHVPE). FeCl2 formed by the reaction between ferrocene (Cp2Fe) and HCl was introduced during GaN growth. Resistivity of the GaN layer increased with increasing Cp2Fe input partial pressure. A semi-insulating (SI)-GaN layer exhibiting room-temperature resistivity of 3.0 × 109 Ω cm was successfully prepared by compensating for the residual donors. The crystalline quality of the GaN layer was found to deteriorate with excess Fe doping. These results indicate that control of background donor impurities is critically important to grow high-quality SI-GaN layers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of thick AlN layer was performed directly on sapphire (0001) substrate at 1100 oC by hydride vapor phase epitaxy (HVPE) using AlCl3 and NH3 as source gases. Growth rate over 10 µm/h was demonstrated by increasing input partial pressure of AlCl3. Also, it was found that the growth rate was sensitive to NH3 input partial pressure (P), and decreased rapidly with increase of P. Edge dislocation density estimated from full width at half maximum (FWHM) of X-ray diffraction (XRD) rocking curves was independent of the growth rate. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth conditions for MnGeP2 thin films have been investigated by using molecular beam epitaxy (MBE) method. Mn and Ge were evaporated by K-cells, and P2 was supplied by decomposing tertialybutylphosphine (TBP). GaAs (001) and InP (001) single crystals were used as substrates. An X-ray diffraction peak, which can be assigned to (008) peak of MnGeP2, was observed at nearly the same position as the (004) peak of GaAs. The lattice constant of the MnGeP2 thin film was determined to be 1.13 nm assuming its crystal structure is a c-axis oriented chalcopyrite type structure. Secondary phases such as GeP, MnGe x and MnP were observed for beam fluxes of Mn and Ge as high as 1×10−8 Torr.