Growth of high quality (In,Ga)N films on O-face ZnO substrates by plasma-assisted molecular beam epitaxy

Epitaxial growth of (In,Ga)N films on O-face ZnO substrates was studied via plasma-assisted molecular beam epitaxy. Atomically smooth GaN films, showing step edges, were grown at low temperatures to suppress the interfacial reaction between nitrides and the ZnO substrate at elevated temperatures using metal-enhanced epitaxy. High-quality growth of ∼300 nm-thick (In,Ga)N films with the In content varying from 11% to 23% was demonstrated using ∼2 monolayer-thick low temperature GaN as the buffer layer. A clear redshift in (In,Ga)N photoluminescence was observed by decreasing the substrate temperature. For the first time, we achieved an atomically smooth surface on 300 nm-thick GaN grown on ZnO, showing step edges. The surface morphology, however, eventually degraded after exposure to the ambient due to strain, which was perhaps facilitated by the formation of an oxide layer. These results are promising for optoelectronics and electronics applications since the eventual degradation of the surface morphology can be mitigated via strain engineering or surface passivation.