Abstract
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°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 1.1×10 18 cm -3 at room temperature.