High-quality ZnMgO films were grown by the radio frequency (RF) magnetron sputtering technique in pure oxygen ambient. Single-crystal films were obtained, when the Mg concentration was Zn0.87Mg0.13O or lower in the case of ZnMgO/Al2O3 and when it was Zn0.65Mg0.35O or lower in the case of ZnMgO/ZnO. Polycrystalline films were obtained when the growth temperature was lower than 500 degrees C, regardless of the Mg concentration. Position of the photoluminescence (PL) ultraviolet (UV) peak of the ZnMgO film shifted with the addition of Mg, from 3.33eV (ZnO) to 3.51 eV (Zn0.87Mg0.13O) and 3.70 eV (Zn0.65Mg0.35O). It was also observed that growth of the ZnMgO films at higher temperature resulted in higher band-gap energy. It was proposed that this phenomenon is because concentration of the substitutional Mg atoms occupying Zn site is increased as the growth temperature increases. (C) 2009 Elsevier B.V. All rights reserved.