We investigate the growth of MgO thin films on Ge(0 0 1) via molecular beam epitaxy and find that the growth temperature plays a key role in the quality of MgO thin films. Reflection high-energy electron diffraction (RHEED) and atomic force microscopy show that the singie-crystal quality and atomically smooth morphology are optimized for a growth temperature of 250 degrees C. RHEED and transmission electron microscopy indicate that the MgO is (0 0 1) oriented and the MgO unit cell has a 45 degrees in-plane rotation with respect to that of Ge, providing a high-quality film and interface for potential spin-injection experiments. (C) 2009 Elsevier B.V. All rights reserved.