This study reports the effect of nitridation on the orientation of GaN layers grown on m-plane sapphire (Al2O3) substrates by hydride vapor phase epitaxy (HVPE). Non-polar (10-10) GaN layers were grown on m-sapphire without nitridation. With increasing nitridation time, the crystallographic phases of the GaN layer changed from non-polar to semi-polar (11-22) through mixed phases of (10-1-3) and (11-22). The phase change with nitridation was attributed to the formation of the nanosized AlN protrusions with slanted facets. This was confirmed by X-ray photoelectron spectroscopy and atomic force microscopy.
Keywords: HVPE; Semi-polar; Non-polar; GaN; Nitridation