Growth of Single-Crystalline, Atomically Smooth MgO Films on Ge(001) by Molecular Beam Epitaxy

Developing single-crystalline FM/MgO/Ge(001) heterostructures is essential for Ge-based spintronics. We investigate the growth of MgO thin films on Ge(001) 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 single-crystal quality and atomically smooth morphology are optimized for a growth temperature of 250\r{ }C. RHEED and transmission electron microscopy indicate that the MgO is (001)-oriented and the MgO unit cell has a 45\r{ } in-plane rotation with respect to that of Ge, providing a high quality film and interface for potential spin injection experiments.