Synthesis of band-gap-reduced p-type ZnO films by Cu incorporation

p -type ZnO thin films with significantly reduced band gaps were synthesized by heavy Cu incorporation at room temperature and followed by postdeposition annealing at 500°C in air for 2h. All the films were synthesized by rf magnetron sputtering on F-doped tin oxide-coated glass. The p-type conductivity was confirmed by Mott-Schottky plots and illuminated I-V analysis. The Cu+1 acceptor states (at substitutional sites) and their band-gap reduction were demonstrated by UV-visible absorption and x-ray excited valence band measurements.