ALTERNATIVE MICROSTRUCTURE OF GAN NUCLEATION LAYERS GROWN BY LOW-PRESSURE METAL-ORGANIC VAPOR-PHASE EPITAXY ON SAPPHIRE SUBSTRATE

Predominately hexagonal GaN nucleation layers were grown on sapphire s ubstrate by low pressure metal-organic vapor phase epitaxy, Tilt angle s of GaN single crystallites about the normal of sapphire substrate ar e determined to be in the range from 0 degrees to 5 degrees by using s elected area electron diffraction. A small portion of cubic phase of G aN was observed to be selectively distributed in the grain boundary ar eas and the instantaneous surface state is suggested to play an import ant role in the nucleation of the Zincblende phase, Phase transition f rom hexagonal to cubic GaN caused by heavy radiation from ion beam was also noticed. A critical temperature is proposed to exist in forming predominately cubic or hexagonal GaN nucleation layer. (C) 1997 Americ an Institute of Physics.