Controlled Growth of Zn-Polar ZnO Films on Al-Terminated α-Al₂O₃(0001) Surface by Using Wurtzite MgO Buffer

The controlled growth of Zn-polar ZnO films on Al-terminated αAl₂O₃ (0001) substrates is investigated by the radio-frequency plasma-assisted molecular beam epitaxy method. Prior to the growth, αAl₂O₃ (0001) surface is modified by an ultrathin MgO layer, which serves as a uniform template for epitaxy of
Zn-polar ZnO films. The microstructures of ZnO/MgO/Al₂O₃ interface are investigated by in-situ reflection high-energy electron diffraction observations and ex-situ high-resolution transmission electron microscopy characterization. It is found that under Mg-rich condition, the achievement of the wurtzite MgO ultrathin layer plays a key role in the subsequent growth of Zn-polar ZnO. An
interfacial atomic model is proposed to explain the mechanism of polarity selection of both MgO and ZnO films.