In this letter, we report on the realization of the p-type ZnO film by in situ nitrogen doping and subsequent thermal activation, as well as the discussions on the doping mechanism. Through the high temperature activation, a conversion of conductivity from n- to p-type with a hole concentration of similar to 10(19)/cm(3) has been observed by Hall measurements, accompanied with the formation and dissociation of N-H complex investigated by Raman spectra. These observations provide probability on the passivation effect of N-H complex and dehydrogenation process at high temperature, as confirmed by the variation of N and H atomic concentration in the secondary ion mass spectra. The dehydrogenation process in oxygen ambient at 900 degrees C led to the dissociation of NO-H complexes, resulting in the formation of isolated No acceptors and compensation to the intrinsic donor-like defects. The N-related acceptor bound exciton in photoluminescence with a small binding energy of 100 meV and high p-type conductivity in activated ZnO:N film imply the important role of dehydrogenation effect to the realization of p-type ZnO. (c) 2008 Elsevier B.V. All rights reserved.