Non-polar a-plane AlN epitaxial films on r-plane sapphire with greatly reduced defect densities obtained by high-temperature annealing

Abstract

This study addresses the difficulty of obtaining high crystalline quality non-polar a-plane AlN films grown epitaxially on r-plane sapphire substrates by applying a high-temperature annealing process to films grown via standard-temperature metal organic chemical vapor deposition. Atomic force microscopy results demonstrate the occurrence of a significant recrystallization process in the AlN films during annealing. Raman spectroscopy measurements reveal that the AlN films are subject to a transition from tensile strain to compressive strain after the annealing process. Transmission electron microscopy analyses demonstrate that the non-polar a-plane AlN films provide an appropriately low dislocation density of 3.7 × 109 cm−2.