A new buffer layer for MOCVD growth of GaN on sapphire

High quality GaN films have been grown on sapphire substrates (C face and A face) by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) using a new buffer layer. With our reactor configuration and growth parameters, a GaN film grown on a single GaN buffer layer appears opaque with high density of hexagonal pits. Using a single A1N buffer layer results in extremely nonuniform morphology with mirror-like areas near the edge of the substrates and opaque areas in the center. The double buffer layer we report here, with GaN as the first layer and A1N as the second, each with an optimized thickness, leads to mirror-like films across the entire substrate. Scanning electron microscopy, photoluminescence, x-ray diffraction, and van der Pauw geometry Hall measurement data are presented to establish the quality of our films. The mechanism for this new buffer layer is also discussed.