Effects of the V/III Ratio of a Low-Temperature GaN Buffer Layer on the Structural and Optical Properties of a-GaN Films Grown on r-Plane Sapphire Substrates by MOCVD

We investigate the effects of the V/III ratio of a low-temperature GaN buffer layer on the growth of the overlaying nonpolar a-plane GaN film grown on r-plane sapphire by metal-organic chemical-vapor deposition (MOCVD). With other experimental conditions keeping fixed, the low-temperature GaN buffer layers are grown under various V/III ratios of 1000, 3000, 6000 and 9000, respectively. The characteristics of the a-plane GaN films are analyzed by scanning electron microscopy, high resolution x-ray diffraction, Raman spectrum, and low temperature photo-luminescence. The results show that the V/III ratio of the buffer layer has significant effects on the crystal quality of the a-plane GaN film, and a V/III ratio of 6000 is found to be the most suitable condition to achieve pit-free flat GaN surface.