Optimization of the surface morphologies and electron mobilities in GaN grown by plasma-assisted molecular beam epitaxy

The morphology and electrical properties of homoepitaxial GaN layers grown by molecular beam epitaxy at 720 degreesC were investigated as a function o f Ga/N ratio. GaN films grown with low Ga/N ratios (N-stable regime) are se mi-insulating and have heavily pitted morphologies. GaN films grown with hi gher Ga/N ratios (intermediate regime) have fewer pits with areas of atomic ally flat surface. The room-temperature electron mobilities in samples grow n in the intermediate regime are greater than 800 cm(2)/V s and increase wi th Ga/N ratio. At the highest Ga/N ratios (Ga-droplet regime), Ga droplets formed on the surface during growth. Although the surface morphology is fre e of pits and atomically flat for films grown within the Ga-droplet regime, the mobility decreases significantly compared to films grown in the interm ediate regime. Room-temperature electron mobilities as high as 1191 cm(2)/V s were measured in a GaN film grown with the highest Ga/N ratio within the intermediate regime. (C) 2000 American Institute of Physics. [S0003-6951(0 0)04444-2].