Joint effect of miscut r-plane sapphire substrate and different nucleation layers on structural characteristics of non-polar a-plane GaN films

Abstract

Non-polar a-plane GaN films with different nucleation layers (NLs) were grown on miscut r-plane sapphire substrates (MRSSs) by metal–organic chemical vapor deposition technique. The joint effect of MRSSs and different NLs on the structural characteristics of a-plane GaN films was investigated intensively. Broad asymmetrical stripes and small triangular pits were observed on the surface of a-plane GaN films grown on MRSSs with a relatively large miscut angle. A significant improvement in crystalline quality was found for the a-plane GaN film grown over a low-temperature GaN (LT-GaN) NL deposited on the MRSS with a miscut angle of 1.0° and the film grown over a high-temperature AlN (HT-AlN) NL deposited on the MRSS with a miscut angle of 2.0° has been achieved. Moreover, the smallest anisotropy in crystalline quality and in-plane strain was achieved with the a-plane GaN film grown over the LT-GaN NL or the HT-AlN NL deposited on the 1.5° MRSS. These results indicate that the structural characteristics of the a-plane GaN film can be affected remarkably by the joint effect of MRSSs and different NLs through lattice modulation.