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Co-doping AlN crystals with Si is found to suppress the unwanted 4.7 eV (265 nm) deep ultraviolet absorption associated with isolated carbon acceptors common in materials grown by physical vapor transport. Density functional theory calculations with hybrid functionals demonstrate that silicon forms a stable nearest-neighbor defect complex with carbon. This complex is predicted to absorb at 5.5 eV and emit at or above 4.3 eV. Absorption and photoluminescence measurements of co-doped samples confirm the presence of the predicted CN-SiAl complex absorption and emission peaks and significant reduction of the 4.7 eV absorption. Other sources of deep ultraviolet absorption in AlN are also discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

We performed a thermodynamic analysis of GaN metalorganic vapor phase epitaxy considering the (0001) and surface states. Surface reconstruction, which depends on growth conditions such as temperature and partial pressure, affects growth processes. To discuss the effects of surface states on growth processes, we investigated the driving force of precursor deposition to form the surface phase defined stoichiometrically. In both N2 and H2 carrier gas cases, we showed surface phase diagrams, calculated driving forces, and discussed the difference in growth orientation. [ABSTRACT FROM AUTHOR]

The composition pulling effect in metalorganic vapor-phase InGaN epitaxy was theoretically investigated by thermodynamic analysis. The excess energies of biaxial-strained InxGa1−xN were numerically calculated using empirical interatomic potentials considering different situations: (i) coherent growth on GaN(0001), (ii) coherent growth on In0.2Ga0.8N(0001), and (iii) bulk growth. Using the excess energies, the excess chemical potentials of InN and GaN alloys were computed. Our results show that compressive strain suppresses In incorporation, whereas tensile strain promotes it. Moreover, assuming chemical equilibrium, the relationship between the solid composition and the growth conditions was predicted. The results successfully reproduced the typical composition pulling effect. [ABSTRACT FROM AUTHOR]

An improved thermodynamic analysis method for vapor-phase epitaxy is proposed. In the conventional method, the mass-balance constraint equations are expressed in terms of variations in partial pressure. Although the conventional method is appropriate for gas–solid reactions occurring near the growth surface, it is not suitable for gas reactions that involve changes in the number of gas molecules. We reconsider the constraint equations in order to predict the effect of gas reactions on semiconductor growth processes. To demonstrate the feasibility of the improved method, the growth process of group-III nitrides by metalorganic vapor-phase epitaxy has been investigated. [ABSTRACT FROM AUTHOR]

We propose a newly improved thermodynamic analysis method that incorporates surface energies. The new theoretical approach enables us to investigate the effects of the growth orientation and surface reconstruction. The obtained knowledge would be indispensable for examining the preferred growth conditions in terms of the contribution of the surface state. We applied the theoretical approach to study the growth processes of InN(0001) and by metalorganic vapor phase epitaxy. Calculation results reproduced the difference in optimum growth temperature. That is, we successfully developed a new theoretical approach that can predict growth processes on various growth surfaces. [ABSTRACT FROM AUTHOR]

The thermal and chemical stabilities of group-III sesquioxides (Al2O3, Ga2O3, and In2O3) were comparatively investigated at an atmospheric pressure at heat treatment temperatures ranging from 250 to 1450 °C in a flow of either N2 or H2. In a flow of N2, the thermal decomposition of α-Al2O3 was not observed at the temperatures investigated, while the decompositions of β-Ga2O3 and c-In2O3 occurred above 1150 and 1000 °C, respectively, with no generation of group-III metal droplets on the surfaces. In contrast, the chemical reactions of α-Al2O3, β-Ga2O3, and c-In2O3 began at low temperatures of 1150, 550, and 300 °C in a flow of H2. Thus, the presence of H2 in the gas flow significantly promotes the decomposition of group-III sesquioxides. The order of thermal and chemical stabilities (α-Al2O3 ≫ β-Ga2O3 > c-In2O3) obtained experimentally was verified by thermodynamic analysis, which also clarified dominant decomposition reactions of group-III sesquioxides. [ABSTRACT FROM AUTHOR]

Homoepitaxial tri-halide vapor-phase epitaxy (THVPE) growth on polar, semipolar, and nonpolar bulk GaN substrates was demonstrated using GaCl3 as the precursor. The influence of the surface orientation of the substrate on GaN growth by THVPE was compared with that observed for GaN grown by hydride vapor-phase epitaxy. The dependence of the GaN growth on the surface orientation of the substrate was confirmed; GaN could be grown on , , , , and but not on , , , or . This behavior was explained to be due to the changes in adsorption energy, the magnitudes of which were estimated by theoretical calculations. [ABSTRACT FROM AUTHOR]

The formation mechanism of AlN whiskers on sapphire substrates during heat treatment in a mixed flow of H2 and N2 was investigated in the temperature range of 980–1380 °C. AlN whiskers grew above 1030 °C after covering the sapphire surface with a thin AlN layer. The existence of pits on the sapphire surface beneath the thin AlN layer was observed. Both AlN whisker and pit densities of samples were on the same order of 108 cm−2. These results suggested the following mechanism. First, the sapphire surface reacts with H2, and the generated Al gas reacts with N2 to form a thin AlN layer on sapphire. Then, the sapphire surface reacts with H2 diffusing to the AlN/sapphire interface. The Al gas escapes through dislocations in the AlN layer to leave pits on the sapphire surface, and finally reacts with N2 to form AlN whiskers on the top surface. [ABSTRACT FROM AUTHOR]

The influence of NH3 input partial pressure on N-polarity InGaN grown by tri-halide vapor phase epitaxy was investigated. It was found that surface morphology, solid composition and optical properties were affected by NH3 input partial pressure. As shown in thermodynamic analyses, the indium content increased due to an increase in the driving force for InN deposition caused by increased NH3 input partial pressure. In addition, the deep level emission around 2.1 eV in photoluminescence measurements drastically decreased at higher NH3 input partial pressures. Ab initio calculations and subsequent secondary ion mass spectrometry measurements suggested the reduction of metal-vacancies and/or carbon impurity incorporation in the InGaN layers. [ABSTRACT FROM AUTHOR]

This is a review article on the current status and future prospects of the research and development on gallium oxide (Ga2O3) power devices. Ga2O3 possesses excellent material properties, in particular for power device applications. It is also attractive from an industrial viewpoint since large-size, high-quality wafers can be manufactured from a single-crystal bulk synthesized by melt–growth methods. These two features have drawn much attention to Ga2O3 as a new wide bandgap semiconductor following SiC and GaN. In this review, we describe the recent progress in the research and development on fundamental technologies of Ga2O3 devices, covering single-crystal bulk and wafer production, homoepitaxial thin film growth by molecular beam epitaxy and halide vapor phase epitaxy, as well as device processing and characterization of metal–semiconductor field-effect transistors, metal–oxide–semiconductor field-effect transistors and Schottky barrier diodes. [ABSTRACT FROM AUTHOR]

Thick Si-doped AlN layers were homoepitaxially grown by hydride vapor phase epitaxy on AlN(0001) seed substrates. Following the removal of the seed substrate, an n-type AlN substrate with a carrier concentration of 2.4 × 1014 cm−3 was obtained. Vertical Schottky barrier diodes were fabricated by depositing Ni/Au Schottky contacts on the N-polar surface of the substrate. High rectification with a turn-on voltage of approximately 2.2 V was observed. The ideality factor of the diode at room temperature was estimated to be ∼8. The reverse breakdown voltage, defined as the leakage current level of 10−3 A/cm2, ranged from 550 to 770 V. [ABSTRACT FROM AUTHOR]

The thermal stability of β-Ga2O3(010) substrates was investigated at atmospheric pressure between 250 and 1450 °C in a flow of either N2 or a mixture of H2 and N2 using a radio-frequency induction furnace. The β-Ga2O3 surface was found to decompose at and above 1150 °C in N2, while the decomposition of β-Ga2O3 began at only 350 °C in the presence of H2. Heating β-Ga2O3 substrates in gas flows containing different molar fractions of H2 demonstrated that the decomposition was promoted by increasing the H2 molar fractions. Thermodynamic analysis showed that the dominant reactions are in N2 and in a mixed flow of H2 and N2. The second-order reaction with respect to H2 determined for the mixed flows agrees with the experimental results for the dependence of the β-Ga2O3 decomposition rates on the H2 molar fraction. [ABSTRACT FROM AUTHOR]

Thick high-purity β-Ga2O3 layers of high crystalline quality were grown homoepitaxially by halide vapor phase epitaxy (HVPE) using gaseous GaCl and O2 on (001) β-Ga2O3 substrates prepared by edge-defined film-fed growth. The surface morphology and structural quality of the grown layer improved with increasing growth temperature. X-ray diffraction ω-rocking curves for the (002) and (400) reflections for the layer grown at 1000 °C had small full widths at half maximum. Secondary ion mass spectrometry and electrical characteristics revealed that the growth of high-purity β-Ga2O3 layers with low effective donor concentration (Nd − Na < 1013 cm−3) is possible by HVPE. [ABSTRACT FROM AUTHOR]

The surface stability, growth process, and structural stability of InGaN and InN are reviewed from a theoretical viewpoint. In 2001, a new theoretical approach based on an ab initio calculation was developed. This theoretical approach enables the investigation of the influence of growth conditions such as partial pressure and temperature on the surface stability. The theoretical approach is applied to the research on the In incorporation efficiency in InGaN grown on nonpolar and semipolar surfaces. The calculation results suggest that the N–H layer formed on such surfaces has a crucial role in In incorporation. Moreover, the structural stability of InN grown by pressurized-reactor MOVPE is reviewed. It was found by the theoretical approach that facet formation causes the spontaneous formation of islands with the zinc-blende structure. [ABSTRACT FROM AUTHOR]