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 2 h. 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.