Surface morphologies of homoepitaxial ZnO on Zn- and O-polar substrates by plasma assisted molecular beam epitaxy

Homoepitaxial ZnO layers are grown on Zn-polar (0001) and O-polar (0001¯) surfaces of single crystal ZnO substrates by plasma assisted molecular beam epitaxy. It is found that the growth conditions to obtain smooth surfaces are significantly different for the two surface polarities. For growth on Zn-polar surface, moderate temperature (650°C) and highly O-rich condition (low Zn∕O2) are required, while high temperature (1000–1050°C) and Zn-rich condition (high Zn∕O2 ratio) are essential for growth on O-polar surfaces.