In this study, Bandgap-reduced p-type ZnO thin films were synthesized through Cu and Ga co-doping. The ZnO:(Cu,Ga) films were synthesized by RF magnetron sputtering in O2 gas ambient at room temperature and then annealed at 500° in air for 2 hours. We found that the carrier concentration tuning does not significantly change the bandgap and crystallinity of the ZnO:Cu films. However, it can optimize the carrier concentration and thus dramatically enhance PEC response for the bandgap-reduced p-type ZnO thin films. The co-doped ZnO:(Ga,N) films were deposited by co-sputtering at room temperature, followed by post-annealing at 500°. We found that the ZnO:(Ga,N) films exhibited greatly enhanced crystallinity compared to ZnO:N films doped with pure N. Furthermore, the ZnO:(Ga,N) films showed much higher N-incorporation than ZnO:N films. As a result, the ZnO:(Ga,N) films showed significantly higher photocurrents than ZnO:N films.