Effects of nitrogen doping of ZnO (ZnO:N) during deposition and after postdeposition annealing have been studied by optical techniques, electronic properties, and the application to metal-semiconductor-metal photodetectors (MSM-PDs). Films of ZnO, nitrogen doped during rf sputtering, show larger grain size, narrower full width at half maximum, band gap emission shift in photoluminescence, and higher conductivity. Postannealing has been studied using tube furnace and rapid thermal annealing in nitrogen. These annealing methods not only reconstruct the lattice structure but also activate the nitrogen in the film to improve the conductivity of the film. The MSM-PDs having high photo to dark current ratio of 10(4) and responsive (R) of 1.79 A/W have been fabricated with those films.