Effects of AlN buffer layer thickness on the crystallinity and surface morphology of 10-µm-thick a-plane AlN films grown on r-plane sapphire substrates

Abstract

10-µm-thick a-plane AlN films containing a low-temperature AlN (LT-AlN) buffer layer and a high-temperature AlN (HT-AlN) film were prepared on r-plane sapphire substrates. The crystallinity of all the samples with different LT-AlN buffer layer thicknesses was improved after thermal annealing and HT-AlN growth, mainly owing to the elimination of domain boundaries and the concurrent suppression of facet formation. The optimum crystallinity of HT-AlN films was obtained with full widths at half maximum of the X-ray rocking curves of 660 arcsec for AlNAlN and 840 arcsec for (0002) using a 200-nm-thick LT-AlN buffer layer.