Analysis of MBE growth mode for GaN epilayers by RHEED

The growth mode of hexagonal GaN epilayers on sapphire(0 0 0 1) surfaces during N 2 plasma-assisted molecular beam epitaxy was investigated using in situ reflection high-energy electron diffraction technique. It was found that the Ga-rich condition results in a flat surface showing streak patterns rather than the N-rich condition, and the intensities of the diffraction spots show behaviors that are different for Ga-rich and N-rich conditions. For the specular spot, oscillation-like intensity variations were observed according to the supply of Ga flux, which depends on Ga flux intensity and substrate temperature. At the lower temperature region, the growth of cubic GaN was observed with its [1 1 1] crystal axis along the normal direction of the sapphire(0 0 0 1) surface.