A comparative study of GaN epilayers grown on sapphire and SiC substrates by plasma-assisted molecular-beam epitaxy

Abstract

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 (1×1) 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.