A COMPARATIVE-STUDY OF GAN EPILAYERS GROWN ON SAPPHIRE AND SIC SUBSTRATES BY PLASMA-ASSISTED MOLECULAR-BEAM EPITAXY

We report structural, electrical, and optical data for GaN samples grown on both 6H-SiC and sapphire substrates. A two-stage substrate preparation procedure was employed for removing oxygen from 6H-SiC and c-plane sapphire substrates without the need for elaborate high-temperature thermal degassing. Both sapphire and SiC substrates were treated with hydrogen plasma to reduce the surface contamination as evidenced by the observation of sharp (1 X 1) reconstruction RHEED (reflected high-energy electrons diffraction) patterns. Thin AlN buffer layers were employed and the crystalline quality of GaN films was studied by temperature-dependent Hall measurements, photoluminescence, and x-ray diffraction. Layers with room-temperature mobilities as high as 580 cm2/V s on SiC substrates were obtained.