Epitaxial single crystalline Cu2O thin films were synthesized by thermal oxidation of Cu films, which were deposited on InN/sapphire using electron beam evaporation. Cu2O on InN shows a better crystalline quality than that on GaN due to a 30 degrees in-plane rotation between Cu2O and InN, which results in a smaller lattice mismatch. As-oxidized Cu2O on GaN or on InN shows an n-type conducting behavior, however, as-oxidized Cu2O on InN presents a higher resistance and a lower electron concentration. A transition from n- to p-type is found after the Cu2O thin films are annealed at 500 degrees C in vacuum. A less Cu2+ absorption of the Cu2O/InN plays an important role to determine the conductive type. (C) 2011 Elsevier B.V. All rights reserved.