Growth of Ga- and N-polar GaN layers on O face ZnO substrates by molecular beam epitaxy

Gallium nitride (GaN) epitaxial layers have been grown on O face (0001¯) zinc oxide (ZnO) substrates by ammonia source molecular beam epitaxy. By adjusting the growth temperature and the III/V ratio during the nucleation stage, GaN layers with Ga (0001) or N (0001¯) polarities have been obtained. We show that low growth temperatures (<550 °C) and Ga-rich conditions lead to Ga-polar layers, whereas higher growth temperatures (>600 °C) and N-rich conditions lead to N-polar layers. Furthermore, the formation of a zinc gallate (ZnGa2O4) interfacial layer between GaN and ZnO has been evidenced, which is responsible for the growth of Ga-polar GaN layers. The structural and optical properties of Ga- and N-polar GaN layers have been characterized and Ga-polar GaN layers exhibit higher crystal quality.