Highly c-axis oriented AlN layers grown on c-plane sapphire substrates by radio-frequency sputter epitaxy at 1080 °C

Abstract

Aluminum nitride (AlN) single-crystalline layers were grown on c-plane sapphire substrates by radio-frequency magnetron sputter epitaxy using N2/Ar mixture ambient gas and 5-N grade Al target. The crystalline structures of the AlN layers depending on substrate temperature and N2 composition ratio in ambient gas, were predominantly studied. The crystalline quality of the AlN layer was improved by elevating substrate temperature, and the full-widths at half-maximum (FWHMs) of X-ray rocking curves (XRC) for both symmetric and asymmetric planes of AlN layers grown at N2 composition ratio of around 25%, became low. The FWHMs of XRC for (0002) diffraction of the AlN layers grown at 1080°C, were less than 20arcsec. The surface root-mean-square roughness of such highly c-axis oriented AlN layer was determined by atomic force microscopy, and was increased from 0.6nm to 1.3nm when AlN layer thickness was varied from 0.15 to 0.7μm.