Fabrication of high-crystallinity a-plane AlN films grown on r-plane sapphire substrates by modulating buffer-layer growth temperature and thermal annealing conditions

Abstract

High-crystallinity a-plane AlN(112̅0) films containing a low-temperature AlN (LT-AlN) buffer layer and a high-temperature AlN (HT-AlN) film were grown on r-plane sapphire(11̅02) substrates. We investigated the effect of the growth temperature and thermal annealing conditions for the LT-AlN buffer layers on the crystallinity and surface morphology. The surface roughness of the buffer layers became smooth with the decrease in growth temperature to 900°C, and the crystallinity of the buffer layers was improved by thermal annealing at temperatures over 1600°C. HT-AlN films were then grown on the annealed LT-AlN buffer layers at 1500°C. The optimum crystallinity of HT-AlN films without any facet formation at the surfaces was obtained with full width at half maximum values of the X-ray rocking curves for AlN(112̅0)//[11̅00]AlN at 770 and (0002) at 640″.