Study of anisotropic crystal and electrical properties for semipolar (11-22) GaN grown on m-sapphire

We studied the anisotropic properties of semipolar (11-22) GaN thin film grown on m-plane sapphire substrate using a metalorganic chemical vapor deposition. Among many growth parameters, it was found that anisotropic crystal qualities and surface morphologies were significantly affected by growth pressure, growth temperature and NH3 flow. The X-ray rocking measurements with different incident beam directions shows that anisotropic crystal properties of semipolar GaN, observed by two directions of [11-2-3] and [1-100], were improved by high temperature, high growth pressure and low NH3 flow. In addition, anisotropic surface morphology was significantly improved by low growth temperature and low growth pressure. Particularly, low NH3 flow would drastically reduce anisotropic crystal properties without changing anisotropic surface morphology. From I-V measurements for semipolar GaN with two different NH3 flows, the resistance difference with two directions of [11-23] and [1-100] was decreased by reducing anisotropic crystal properties. Therefore, we believed that low NH3 flow was one of major growth parameters to reduce anisotropic crystal and electrical properties of semipolar (11-22) GaN template.