Morphological Characteristics of a-Plane GaN Grown on r-Plane Sapphire by Metalorganic Vapor-Phase Epitaxy

摘要

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 μm when GaN is grown at 1120℃ on a 40-nm-thick low-temperature GaN (LT-GaN) buffer layer, as well as at 1150℃ 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 x 10~(18) cm~(-3) at room temperature.