Epitaxial ZnO thin films were grown by pulsed laser deposition (PLD) in N-2 or N2O or O-2 background gas on MgO-buffered a-plane sapphire. The excitonic room-temperature cathodoluminescence (CL) intensity, the carrier concentration and the Hall mobility showed well-defined maxima for films grown at PLD gas pressures of ca. I mbar N-2, N2O, and O-2. However, despite the comparable high CL intensities of the ZnO films grown in the three different background gases, their surface toughness varied considerably. Films with rough surface showed a broadening and splitting of the room-temperature CL peak into maxima at 3.21 and 3.26 eV, which could be due to either grain morphology or spatial variation of the electronic defect structure. (c) 2005 Elsevier B.V. All rights reserved.