Influence of surface structure of (0001) sapphire substrate on the elimination of small-angle grain boundary in AlN epilayer

AlN epilayers were grown on (0001) sapphire substrates by metal-organic vapor phase epitaxy, and the influence of the substrate’s surface structure on the formation of in-plane rotation domain is studied. The surface structure is found to change with increasing temperature under H2 ambient. The ML steps of sapphire substrate formed during high-temperature (HT) thermal cleaning is found to cause the formation of small-angle grain boundary (SAGB). To suppress the formation of such structure, the use of LT-AlN BL technique was demonstrated, thereby eliminating the SAGB. The BL growth temperature (Tg) is also found to affect the surface morphology and structural quality of AlN epilayer. The optical emission property by cathodoluminescence (CL) measurement showed higher emission intensity from AlN without SAGB. The LT-AlN BL is a promising technique for eliminating the SAGB.