Homoepitaxial growth of AlN layers on freestanding AlN substrate by metalorganic vapor phase epitaxy

•We examine the crystallinity of the homoepitaxially grown AlN layer on freestanding AlN substrate.•With lower V/III ration of 80, many hillocks were observed on AlN layer because of mixed polarity of AlN.•By optimizing the V/III ratio and growth temperature, homoepitaxial AlN layers with good surface flatness and high crystallinity could be realized.

We investigated the optimum conditions for the homoepitaxial growth of AlN on freestanding AlN (0001) substrates (off angle: 0.6–0.9°) by metalorganic vapor phase epitaxy. The crystallinity, surface morphology, and full width at half maximum as obtained from X-ray rocking curves of the homoepitaxially grown AlN layer were strongly dependent on the growth conditions. When AlN layers are grown on an AlN substrate using a relatively low V/III ratio of 80, which is commonly used for AlN layer growth on a sapphire substrate, a high density of hillocks appeared at the AlN surface. In addition, the crystallinity of these hillocks was significantly worse than that of the substrate. By optimization of the growth temperature and V/III ratio, homoepitaxial AlN layers with good surface flatness and high crystallinity were realized.