In this study, co-doped ZnO:(Ga,N) and ZnO:(Al,N) films were deposited by co-sputtering at room temperature and 100°C, followed by post-annealing at 500°C. Nitrogen-doped ZnO films, ZnO:N(1) and ZnO:N(2), were deposited at substrate temperatures of 500°C and 100°C, respectively. We found that the ZnO:(Ga,N) and ZnO:(Al,N) films exhibited greatly enhanced crystallinity compared to ZnO:N(1) and ZnO:N(2) films doped with pure N. Furthermore, the ZnO:(Ga,N) and ZnO:(Al,N) films showed much higher N-incorporation than ZnO:N films grown at 100°C and 500°C with pure N doping. As a result, the ZnO:(Ga,N) and ZnO:(Al,N) films showed significantly higher photocurrents than ZnO:N(1) and ZnO:N(2) doped by N alone at both high and low temperatures. Our results suggest that the passive co-doping approach is a preferred method for synthesizing metal oxides with both high crystallinity and impurity incorporation, which should help to improve their photoelectrochemical performance.