Evaluation of growth methods for the heteroepitaxy of non-polar (112¯0) GAN on sapphire by MOVPE

Non-polar a-plane gallium nitride (GaN) films have been grown on r-plane (11¯02) sapphire by metal organic vapour phase epitaxy (MOVPE). A total of five in situ defect reduction techniques for a-plane GaN are compared, including two variants with a low temperature GaN nucleation layer (LTNL) and three variants without LTNL, in which the high-temperature growth of GaN is performed directly on the sapphire using various crystallite sizes. The material quality is investigated by photoluminescence (PL), X-ray diffraction, cathodoluminescence, atomic force and optical microscopy. It is found that all layers are anisotropically strained with threading dislocation densities over 109 cm−2. The PL spectrum is typically dominated by emission from basal plane stacking faults. Overall, growth techniques without LTNL do not yield any particular improvement and even result in the creation of new defects, i.e. inversion domains, which are seldom observed if a low temperature GaN nucleation layer is used. The best growth method uses a LTNL combined with a single silicon nitride interlayer.