Growth mode in strained ZnO films on Al₂O₃(0001) during sputtering

We investigated the temperature dependence of growth mode in highly mismatched sputter-grown ZnO/Al₂O₃(0001) heteroepitaxial films using real-time synchrotron X-ray scattering. We find that the growth mode changes from 2 dimensional (2D) layer to 3D island in early growth stage with temperature (300°C-500°C). At around 400°C, however, intermediate 2D platelets nucleate in early stage, act as nucleation cores of 3D islands and transform to misaligned state during further growth. The results of the strain evolution during growth suggest that the surface diffusion is a major factor in determining the growth mode in the strained ZnO/Al₂O ₃(0001) heteroepitaxy.