Control of polarity of ZnO films grown by plasma-assisted molecular-beam epitaxy: Zn- and O-polar ZnO films on Ga-polar GaN templates

We report on the growth of polarity-controlled ZnO films by plasma-assisted molecular-beam epitaxy. Different polar (Zn- and O-polar) ZnO films on uni polar (Ga-polar) GaN epilayers are selectively grown. Polarity of ZnO films is evaluated by coaxial impact collision ion scattering spectroscopy. Zn p reexposure prior to ZnO growth results in Zn-polar ZnO films (Zn face), whi le O-plasma preexposure leads to the growth of O-polar ZnO films (O face). High-resolution transmission electron microscopy reveals the formation of a n interface layer between ZnO and GaN epilayers in O-plasma preexposed samp les, while no interface layer is observed in Zn preexposed samples. The int erface layer is identified as single crystalline, monoclinic Ga2O3. We prop ose models for interface configurations at ZnO/GaN heterointerfaces, which can successfully explain the different polarities of the ZnO films. (C) 200 0 American Institute of Physics. [S0003-6951(00)02149-5].