Dislocation Reduction in GaN Epilayers Grown on a GaNP Buffer on Sapphire Substrate by Metalorganic Chemical Vapor Deposition

Dislocation defects in a GaN epilayer grown on a low-temperature GaN-rich GaNP (LT-GaNP) buffer on sapphire substrate by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) were investigated by means of transmission electron microscopy and atomic force microscopy. The GaNP-buffer-based high-temperature GaN (HT-GaN) layers have a dislocation density as low as 5×10 8 cm -2 , which can be compared to the best results for GaN epilayers grown on sapphire by atmospheric pressure MOCVD using the conventional LT-GaN or -AlN buffer. The dislocation density reduction could be predominately attributed to an enhanced lateral overgrowth for the HT-GaN layer grown on a GaNP buffer, which is confirmed by the observation of a special morphology evolution beginning from the GaNP buffer.