Zn-1 xMgxO films with x=0.22-0.87 were grown on MgO (100) substrates by molecular beam epitaxy at 400 and 600 degrees C respectively. The films containing 85% or less ZnO grow epitaxially and retain entirely the rocksalt (rs) crystal structure. The rs-Zn-1 xMgxO epilayers have a tunable bandgap energy of 4.5-6.2 eV. In addition, the rs-Zn-1 xMgxO epilayer grown at 600 degrees C exhibits a lower FWHM value of its (200) rocking curve as compared to its low-temperature counterpart. The lattice constant of rs-ZnO at ambient pressure and temperature is obtained to be 4.2766 angstrom. The sticking coefficient of Mg atoms on rs-ZMO is approximately four times higher than that of ZnO atoms regardless of the growth temperature in the range of 400-600 degrees C. (C) 2017 Elsevier B.V. All rights reserved.