The effects of V/III ratio on nonpolar a-plane GaN films grown on r-plane sapphire by MOCVD

Abstract

It was critical to optimize V/III ratio for growing high quality GaN epilayers, because a suitable V/III ratio can promote the two-dimensional growth mode and decrease the crystalline anisotropy. In this paper, in order to investigate the influence of the V/III ratio on the surface morphology and the crystal quality of nonpolar a-GaN, a-plane GaN thin films with different V/III ratios were grown on r-plane sapphire substrates with low-temperature (LT) GaN buffer layers (BLs) by metal-organic chemical-vapor deposition (MOCVD). The surface morphology of these a-GaN thin films was characterized by optical microscopy (OM) and atomic force microscopy (AFM). The crystal quality of the a-GaN thin films was investigated by high resolution X-ray diffraction (HRXRD). The results showed that the a-GaN thin films with a V/III ratio of 1200 had the smoothest surface morphology with a root mean square (RMS) surface roughness of 1.6 nm and the best crystal quality with a iiill-width-at-half-maximum (FWHM) of (11 2̄ 0) x-ray rocking curve of 864 arcsec.