Novel buffer layer for the growth of GaN on c‐sapphire

Abstract

AbstractWe propose a rocksalt (RS) structured chromium nitride (CrN) layer as a novel buffer for the growth of gallium nitride (GaN) films on c‐sapphire substrate. A RS‐CrN buffer has good advantages for growing GaN films on c‐sapphire from the viewpoints of lattice mismatch and thermal expansion coefficient. The RS‐CrN layer has mid value of both the lattice constant and the thermal expansion coefficient of GaN and c‐sapphire. It is verified that the lattice mismatch between CrN and c‐sapphire of 6.2–6.7%, which is experimentally estimated from reflection high‐energy electron diffraction (RHEED) characterization, about 6.2–6.7%, agree well with the calculated value of 6.6%. By these advantages, N‐polarity GaN epilayers grown on RS‐CrN buffer layer show remarkably improved crystal quality when compared with those of grown on conventional low temperature (LT) GaN buffer using molecular beam epitaxy (MBE). For a further improvement of GaN crystallinity, we performed the surface treatment of Ga‐exposure on CrN buffer layer. The Ga‐exposure treatment on the RS‐CrN buffer layer drastically improved the crystal quality of upper GaN epilayer, which was identified by measuring structural and optical properties using X‐ray diffraction (XRD) and Photoluminescence (PL), respectively. The improved crystallinity is resulted not from the polarity conversion but from the stress relaxation effect by a metallic Ga interlayer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)