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

Abstract

We fabricated the homoepitaxial AlN layers and AlGaN/AlN multi-quantum wells (MQWs) grown on freestanding AlN (0001) substrates by metalorganic vapor phase epitaxy. Crystallographic and optical characteristics of these AlN layers and AlGaN/AlN MQWs were investigated by X-ray diffraction (XRD), SEM, AFM, PL, and so on. These characteristics of MQWs are strongly dependent on growth condition of homoepitaxial AlN layer. In case that AlN layers are grown with high temperature and low V/III ratio, there are many hillocks on the surface and no PL signal from MQW. In contrast, strong PL emission cannot be obtained from AlGaN/AlN MQW on AlN layer grown with lower temperature and higher V/III ratio, because this MQW has large surface roughness from results of XRD and AFM measurement. We optimized the growth condition of AlN layers and obtained the high quality AlGaN/AlN MQW with smooth surface, strong PL emission.