High quality epitaxial MgxZn1-xO films are essential for the fabrication of ZnO/MgxZn1-xO heterostructures. In this work, MgxZn1-xO (0less than or equal toxless than or equal to0.33) thin films are epitaxially grown on (0112) r-sapphire substrates by metalorganic chemical vapor deposition. A thin ZnO buffer layer in the order of 50 Angstrom is found to be critical for the growth of single crystal MgxZn1-xO (0less than or equal toxless than or equal to0.33) films with a wurtzite-type structure. The energy bandgap of MgxZn1-x-O films as a function of Mg composition was deduced using a UV-Visible spectrophotometer at room temperature in conjunction with Rutherford backscattering spectroscopy measurements. The epitaxial relationship between the wurtzite-type MgxZn1-xO films and r-sapphire substrates is determined to be (1120) Mg(x)Zn(1-x)Oparallel to(0112) Al2O3, and [0001] Mg(x)Zn(2-x)Oparallel to[0111] Al2O3. In-plane X-ray diffraction reflections show the lower lattice mismatch along the c-axis of the MgxZn1-xO films on r-sapphire substrates. High resolution transmission electron microscopy analysis of the film/substrate interface indicates the region in the film near the interface is crystalline though strained. (C) 2003 Elsevier B.V. All rights reserved.