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 deposi tion (MOCVD) using a new buffer layer. With our reactor configuration and growth parameters, a GaN film grown on a single GaN buffer layer a ppears opaque with high density of hexagonal pits. Using a single AW b uffer layer results in extremely nonuniform morphology with mirror-lik e 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 AIN as the second, each with an optimized thickness, leads to mirr or-like films across the entire substrate. Scanning electron microscop y, photoluminescence, x-ray diffraction, and van der Pauw geometry Hal l measurement data are presented to establish the quality of our films . The mechanism for this new buffer layer is also discussed.