Investigation of Buffer Iayer of Cubic GaN Epitaxial Films on (100) GaAs Grown by Metalorganic-Hydrogen Chloride Vapor-Phase Epitaxy

Cubic GaN epitaxial layers are grown with GaN buffer layers of various thicknesses on (100) GaAs substrate using (CH3)3Ga, HCI and NH3 as starting materials. The full width at half-maximum (FWHM) of the X-ray peak, the surface roughness and the PL spectra show that the optimum thickness of the GaN buffer layer ranges from 20 to 50 nm. It is found by high-resolution TEM and electron diffraction measurements that a GaN buffer layer grown at 500° C is a polycrystal and becomes a single crystal upon thermal annealing at 850° C for 10 min prior to the growth of a cubic GaN epitaxial layer.