High-quality ZnMgO/ZnO multi-layer thin films in a-plane orientation were grown by pulsed laser deposition on r-plane sapphires. Reflection high-energy electron diffraction (RHEED) patterns were performed to monitor the growth morphology and the epitaxy. X-ray diffraction, RHEED, and atomic force microscopy show that anisotropic growth of a-plane ZnO results in stripe morphology, and the difference of thermal expansion between ZnO and sapphire plays a significant role on the film surface smoothness. Cross-sectional transmission electron microscopy identifies the cause of disorientation of ZnO growth on sapphire. (C) 2007 Elsevier B.V. All rights reserved.