ZnO and related materials: Plasma-assisted molecular beam epitaxial growth, characterization, and application

This paper will address features of plasma-assisted molecular beam epitaxial growth of ZnO and related materials and their characteristics. Two-dimensional, layer-by-layer growth is achieved both on c-plane sapphire by employing MgO buffer layer growth and on (0001) GaN/Al₂O₃ template by predepositing a low-temperature buffer layer followed by high-temperature annealing. Such two-dimensional growth results in the growth of high-quality heteroepitaxial ZnO epilayers. Biexciton emission is obtained from such high quality epilayers. The polarity of heteroepitaxial ZnO epilayers is controlled by engineering the heterointerfaces. We achieved selective growth of Zn-polar and O-polar ZnO heteroepitaxial layers. The origin of different polarities can be successfully explained by an interface bonding sequence model. N-type conductivity in Ga-doped ZnO epilayers is successfully controlled. High conductivity, enough to be applicable to devices, is achieved. Mg_xZn_1-xO/ZnO heterostructures are grown and emission from a ZnO quantum well is observed. Mg incorporation in a MgZnO alloy is determined by in-situ reflection high-energy electron diffraction intensity oscillations, which enables precise control of the composition. Homoepitaxy on commercial ZnO substrates has been examined. Reflection high-energy electron diffraction intensity oscillations during homoepitaxy growth are observed.