Synthesis and characterization of band gap-reduced ZnO:N and ZnO:(Al,N) films for photoelectrochemical water splitting

ZnO thin films with significantly reduced band gaps were synthesized by doping N and codoping Al and N at 100 °C. All the films were synthesized by radiofrequency magnetron sputtering on F-doped tin-oxide-coated glass. We found that codoped ZnO:(Al,N) thin films exhibited significantly enhanced crystallinity compared with ZnO doped solely with N, ZnO:N, at the same growth conditions. Furthermore, annealed ZnO:(Al,N) thin films exhibited enhanced N incorporation over ZnO:N films. As a result, ZnO:(Al,N) films exhibited better photocurrents than ZnO:N films grown with pure N doping, suggesting that charge-compensated donor–acceptor codoping could be a potential method for band gap reduction of wide-band gap oxide materials to improve their photoelectrochemical performance.