INFLUENCE OF MOISTURE AND OXYGEN ON THE FORMATION OF CUBIC PHASE GAN IN HALIDE VAPOR-PHASE EPITAXIAL-GROWTH

Halide vapor phase epitaxy (HVPE) was performed for the growth of GaN films. The hexagonal phase alpha-GaN films were grown on (0001) and (< 11(2)over bar 0>) sapphire substrate, using the Ga/HCl/NH3/He system. Reflection high energy electron diffraction (RHEED) and scanning elect ron microscopy (SEM) were used for the study of phase orientation and surface morphology of the resulting films. Luminescence was assessed b y photoluminescence (PL) and local cathodoluminescence (CL) measuremen ts at room temperature. It was observed that the oriented islands of c ubic gallium nitride (beta-GaN) were formed on the surface of as-grown alpha-GaN films. Their growth occurred during: postgrowth, when the t emperature in the deposition zone decreased. It was shown that the gro wth of the beta-GaN islands was caused by the presence of trace moistu re and oxygen remained in the gas phase. Apart from the partial pressu res of H2O vapor and oxygen the growth conditions of alpha-GaN films s howed a significant effect on the density of the resulting islands. Po ssible reasons for the formation of beta-GaN followed by subsequent gr owth are discussed.