The ZnO and mixed (ZnO:GaN) thin films are synthesized by (RF) magnetron sputtering in Ar and mixed O-2 and N-2 gas ambient at 100 degrees C, followed by post-annealing at 500 degrees C in ammonia for 4 h. The mixed (ZnO:GaN) thin films deposited under Ar gas ambient failed to reduce the bandgap, whereas (ZnO:GaN) thin films grown under mixed O-2 and N-2 gas ambient showed bandgap reduction. The (ZnO:GaN) films deposited under mixed O-2 and N-2 gas exhibited enhanced crystallinity, with shifting the optical absorption into the visible light regions. The bandgap reduction in mixed (ZnO:GaN) thin films is realized by varying the RF power. As a result, mixed (ZnO:GaN) films grown under mixed O-2 and N-2 showed higher photocurrents than the mixed (ZnO:GaN) thin films deposited under Ar gas ambient. Our results indicate that reduced bandgap with enhanced PEC response can be attained using the appropriate gas ambient and by varying the RF power using mixed (ZnO:GaN) films. (C) 2013 Elsevier B.V. All rights reserved.