This work investigated the influence of Zn/O flux ratio and Mn-doped ZnO buffer layer on the epitaxial growth of ZnO grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Atomic force microscopy (AFM), photoluminescence (PL) and X-ray diffraction (XRD) measurements indicated that a small amount residual strain of ZnO epilayers was further relaxed under stoichiometric growth conditions due to the better surface migration of the adatoms. Moreover, we observed that a small amount of Mn doping led to obtain a flatter surface with stronger lattice relaxation maybe due to the greatly enhanced surface migration of the adatoms. By adding a Mn-doped ZnO buffer layer the optical and electrical properties of the ZnO epilayers had significant improvement. (c) 2008 Elsevier B.V. All rights reserved.