NUCLEATION LAYER EVOLUTION IN METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITIONGROWN GAN

The structure and morphology of low growth temperature GaN nucleation layers have been studied using atomic force microscopy (AFM), reflecti on high energy electron diffraction (RHEED), and transmission electron microscopy (TEM). The nucleation layers were grown at 600 degrees C b y atmospheric pressure metalorganic chemical vapor deposition (MOCVD) on c-plane sapphire. The layers consist of predominantly cubic GaN (c- GaN) with a high density of stacking faults and twins parallel to the film/substrate interface. The average grain size increases with increa sing layer thickness and during the transition from low temperature (6 00 degrees C) to the high temperatures (1080 degrees C) necessary for the growth of device quality GaN. Upon heating to 1080 degrees C the n ucleation layer partially converts to hexagonal GaN (h-GaN) while reta ining a high stacking fault density. The mixed cubic-hexagonal charact er of the nucleation layer region is sustained after subsequent high-t emperature GaN growth. (C) 1996 American Institute of Physics.