A single-phase wurtzite MgZnO film with an optical band gap of 294.5 nm was synthesized on ZnO substrate by molecular beam epitaxy, and a photodetector was fabricated working in the ultraviolet-B spectrum region. Wurtzite BeO was adopted to restrain the substrate response as an insulating layer and provide an excellent epitaxial template for high-Mg-content MgZnO growth. In situ reflection high-energy electron diffraction observations, ex situ X-ray diffraction and reflectance spectrum indicate the achievement of high-quality single-phase wurtzite MgZnO with smooth surface and deep ultraviolet band gap. The BeO layer efficiently suppresses the photoresponse from the substrate, as the photo-detector demonstrates a sharp cutoff at 290 nm, consistent with the optical band gap. (C) 2013 Elsevier B.V. All rights reserved.