Formation mechanism of (10−13) AlN twins on m-plane sapphire substrates at high temperature by hydride vapor phase epitaxy

Abstract

(10−13) AlN twin structures were grown on m-plane sapphire substrates with high-temperature nitridation by hydride vapor phase epitaxy. The formation mechanism of the (10−13) AlN twins was studied. It was found that a wavy interface with nano-scale pits formed between the sapphire and AlN epilayer. The wavy surface of the m-plane sapphire was composed of two kinds of equivalent nano-scale a-planes of (11−20) and (2−1−10), on which (0001) AlN was grown. If the two kinds of nano-scale AlN grains with different orientations were adjacent, then the (10−13) AlN twins formed. Actually, the twin structures were already formed during the high-temperature nitridation of the sapphire, and the wavy surface also came from this process, which further confirmed that the nano-scale wavy surface of the sapphire resulted in the twin structure. The results are helpful to understand the kinetic growth process and improve the crystal quality of (10−13) AlN.