Cathodoluminescence spectra and electrical properties of the N doped and N-Al codoped p-type ZnO films and the dependence of these two properties on the post-annealing were investigated. Spectral analyses show that the intensity of the green emission strongly depends on the annealing ambient and closely relates with the width of the electron depletion region at the particle boundary. The conducting type and electrical properties of N doped and N-Al codoped ZnO films are greatly affected by the annealing process. The grain boundary effect was proposed to explain the green emission behavior and the p-type conduction in polycrystalline ZnO based films. (c) 2006 Elsevier B.V. All rights reserved.