Epitaxial growth of ZnO thin films on $R$-plane sapphire substrate by radio frequency magnetron sputtering

ZnO thin films were deposited on a $R$-plane sapphire substrate. The effects of the thermal energy and the kinetic energy of the sputtered species on the growth of ZnO thin films were investigated. By varying the substrate temperature, chamber pressure, and radio frequency power, the structure of ZnO thin films was transformed from polycrystalline to epitaxial on $R$-plane sapphire substrates. High quality (110) ZnO epitaxial thin films were grown at the condition of 400 °C, 250 W, and 5 mTorr. According to reflection high energy electron diffraction and reflection electron microscopy observations, there were no double diffraction distortion and any other patterns. Its surface roughness observed by atomic force microscopy was about 27 nm.