A model of reaction pathways of GaN growth by metalorganic vapor-phase epitaxy was studied by computational fluid dynamics simulations. We included the formation of polymers such as [Ga–N] n and [MMGaNH] n (n=2–6) in the reaction model in a TMGa/NH3/H2 system for the first time. The simulations using this reaction modeling successfully explained experimental growth rates at various temperatures, and clarified the main reaction pathway of GaN growth. The change in gas-phase chemistry due to temperature in the range of 300–1400 K was investigated. It was found that the type of reactive molecule changes with temperature, followed by the formation of different polymers in a certain temperature range, that is, [MMGaNH] n at 600–750 K and [Ga–N] n at higher temperatures.

The photoelectrochemical properties of In x Ga1-x N (x=0.02 and 0.09) were compared with those of GaN. The band-edge potentials of In x Ga1-x N were determined by the Mott–Schottky plot for the first time. The gas generation from a counterelectrode using the In0.02Ga0.91N working electrode was the highest of the three samples. Band-edge potentials and the light absorption of a working photoelectrode presumably affect the gas generation efficiency.

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We report the morphological evolution of a-plane GaN thin films grown on r-plane sapphire substrates by atmospheric metalorganic vapor-phase epitaxy. The surface flatness is improved under optimized growth conditions which are different from those of c-plane epitaxy. The peak-to-valley height of surface roughness is reduced from 4 to 0.8 mm when GaN is grown at 1120 C on a 40-nm-thick low-temperature GaN (LT-GaN) buffer layer, as well as at 1150 C on a 20-nm-thick LT-GaN. These samples show their highest electron mobility of 220 cm 2 /(V s) at an electron concentration of 1:1 Â 10 18 cm À3 at room temperature.