Effects of oxygen partial pressure within the Ar process plasma on the optical, structural, and electrical properties of magnetron-sputtered ZnMgBeO films were investigated in detail. It was observed that the optical energy bandgap (E-g) values of the ZnMgBeO films substantially decrease with the oxygen addition, from 5.3 to 4.3 eV as the oxygen partial pressure increases from zero to one. The full-widthat-half-maximum (FWHM) values of the (0 0 0 2) XRD peaks drastically decrease with the addition of a small amount of oxygen but then increase with further oxygen addition. All the films had very high sheet resistance, 1.3-1.4 G Omega/square. It was also observed that the concentration of Zn within the films significantly increased with the oxygen addition, which was proposed to be mainly responsible for the observed decrease in E-g. It was also proposed that the FWHM change due to the oxygen addition may be attributable to three factors, film composition, grain size, and point defect density, as confirmed by results of TEM and XPS investigations. (c) 2015 Elsevier B.V. All rights reserved.