Optimization of (112¯0) a-plane GaN growth by MOCVD on (11¯02) r-plane sapphire

A-plane GaN (112¯0) epilayers have been grown on r-plane (11¯02) sapphire by MOCVD, and investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). This particular orientation is non-polar, as opposed to the c-direction, and avoids polarization charge and the associated screening charge, and the consequent band bending. Our results showed that low pressure, low ammonia flow rate (namely low V/III ratio), high-temperature conditions lead to fully coalesced and relatively high crystalline-quality a-plane GaN films. Both low-temperature GaN buffer and high-temperature AlN buffer were used for a-plane GaN growth on r-plane sapphire, and produced similar crystalline quality and surface morphology. Surface morphological evolution during early stages of a-plane GaN growth revealed behavior different from that of c-plane GaN growth. The possible reasons for striped features and surface undulations of a-plane GaN are discussed.