Shingo Mochizuki

Systematic analysis and control of low-temperature GaN buffer layers on sapphire substrates

The growth of low-temperature (LT) GaN buffer layers on sapphire substrates was systematically studied using x-ray photoelectron spectroscopy with regards to processes such as substrate treatment and deposition conditions, along with annealing treatments of the GaN buffer layer during two-step metalorganic chemical vapor deposition. Variations observed in the LT-buffer layer depended strongly on both the chemical state of the sapphire surface as a result of the substrate treatment and the subsequent annealing conditions. A 20 nm buffer layer on non-nitrided sapphire evaporated after the formation of islands during the conventional annealing process (N2, H2, and NH3 gas mixture). Adding H2 gas to the annealing ambient enhanced the evaporation and reduced the surface coverage. It was found that AlxGa1−xN was formed at the interface, which has a low evaporation coefficient. In contrast, a buffer layer deposited onto a nitrided sapphire substrate evaporated completely in a layer-by-layer mode. The buffer laye...

Growth Mechanism and Characterization of Low‐Dislocation‐Density AlGaN Single Crystals Grown on Periodically Grooved Substrates

We have implemented the direct growth technique using periodically grooved substrates of sapphire(0001), sapphire(1120) and 6H-SiC(0001) Si in growing low-dislocation-density AlGaN with AIN molar fractions below 0.14. Low dislocation densities observed in lateral growth areas were in the range of 10 7 cm -2 or less which was similar to those of GaN prepared by the same technique. Besides, we also found that doping Mg into AlGaN films assisted in lateral growth very effectively and hence lateral coalescence was made possible in shorter growth time.

Crystal Growth of High‐Quality AlInN/GaN Superlattices and of Crack‐Free AlN on GaN: Their Possibility of High Electron Mobility Transistor

Al 0.90 In 0.10 N/GaN, AIN/GaN and their superlattices (SLs) grown on GaN by metalorganic vapor phase epitaxy (MOVPE) were studied. A (0001) sapphire substrate was used. X-ray diffraction analysis of 2θ/ω scans and reciprocal space mapping showed that the samples were coherently grown on GaN, and in particular, crack-free AlN of 0.5 μm thickness was grown on GaN. Al 0.90 In 0.10 N/GaN (or AlN/GaN) SLs grown on GaN showed a maximum electron mobility of 946 (or 1422) cm 2 /Vs at room temperature and a nominal sheet carrier density of 2.9 x 10 12 (or 7.5 x 10 12 ) cm -2 .

Reduction of threading dislocation density in AlXGa1−XN grown on periodically grooved substrates

We proposed a heteroepitaxial lateral overgrowth technique using periodically grooved substrates to prepare a GaN single crystal with low dislocation density. By this technique, GaN single crystals have been grown without a selective growth mask or GaN single crystal seeds. Moreover, the AlGaN single crystal, which is important for optoelectronic devices in the UV region, can also be grown using this technique. The reduction of the threading dislocation density in Al x Ga 1-x N single crystals grown on periodically grooved substrates was confirmed by transmission electron microscopy.

Metalorganic Vapor Phase Epitaxial Growth of High-Quality AlInN/AlGaN Multiple Layers on GaN

Al1-xInxN epilayers with a thickness of 20 nm grown on GaN were characterized. It was found that the surface roughness of very thin Al1-xInxN is more sensitive to the growth temperature than to the lattice mismatch to GaN. Multiple layers of (Al0.95In0.05N/Al0.10Ga0.90N)5 were grown at different temperatures. X-ray diffraction measurement revealed that the sample grown at 800°C is of high quality, showing up to five orders of sharp satellite peaks, while no clear satellite peaks are observed from the sample grown at 720°C. Transmission electron microscopy observation revealed that multiple layers grown at 800°C exhibit very sharp interfaces.

Low-dislocation-density AlxGa1−xN single crystals grown on grooved substrates

Abstract We propose a new approach to the direct growth of low-dislocation-density Al x Ga 1− x N single crystal films on highly mismatched substrates. Four different substrates, basal-plane sapphire (0001) and (11 2 0), 6H–SiC(0001) Si and Si(111), were used. The surface of the substrates was patterned with periodic grooves. In this technique, neither a selective growth mask nor a patterned GaN single crystal film were used. Low-dislocation-density areas were observed above the trench area and at the boundaries of the terrace and trench areas. The dislocation density was reduced to mid 10 6 cm −2 which is lower than that of the films grown directly on the planar substrates by at least two orders of magnitude.

MOVPE growth and characterization of Al1−xInxN/GaN multiple layers

Abstract In a previous study, we have found that lattice matching is essential to grow high quality thick Al 1− x In x N on GaN epilayer. In this study, in a coherent growth regime, it is found that high-quality Al 1− x In x N with different composition can be successfully grown on the GaN epilayer. The surface morphology and the roughness of very thin Al 1− x In x N grown on GaN epilayer were similar regardless of the InN molar fraction x in the range from 0.07 to 0.34. (Al 1− x In x N/GaN) 5 thin multiple layers were grown on the GaN epilayer. All samples show atomically flat interfaces which was confirmed by X-ray diffraction measurement and transmission electron microscopy.