An improved MBE-grown ZnO film on nitrided sapphire was obtained by introducing an MgO buffer layer before the ZnO growth. The effect of MgO layer was systematically studied by transmission electron microscopy investigations. It was found that the island feature of MgO buffer promoted the strain relaxation of the nitrided layer, which, in turn, improved the quality of the ZnO film. (c) 2007 Elsevier B.V. All rights reserved.