Contrasting morphologies of O-rich ZnO epitaxy on Zn- and O-polar thin film surfaces: Phase-field model

The island growths during the epitaxy of differently polar ZnO thin films under O-rich condition are simulated in terms of a phase-field model. The different island nucleation modes as well as the different atom migration and influx sticking ability are considered on the Zn-polar surfaces and the O-polar ones. By reproducing the morphological variation from the smooth two-dimensional island growth on the Zn-polar surfaces to the rough three-dimensional islands on the O-polar surfaces, our simulated results indicate that the surface morphology of the ZnO thin films is dependent not only on the migration ability and influx rate but also on the island nucleation kinetics. For the Zn-polarity, the easy island nucleation contributes to the smooth morphology as a result of the limited migration and fast influx. However, the reduced nucleation kinetics on the O-polar surfaces causes the developed three-dimensional island growth. This phase-field modeling should be applicable to other semiconductor epitaxial growths.