Optical properties of Cu-doped thin ZnO films

Cu-doped ZnO films grown on Si (001) wafers and quartz substrates were prepared with a radio-frequency reactive magnetron sputtering method. X-ray diffraction, transmittance spectra, photoluminescence spectra, and calculation based on the density functional theory are used to analysis the crystal structure, optical properties, and band structure. All the Zn_1-xCu_xO films are highly (001) textured without any precipitated phase, and Cu dopants hardly change the c parameter of ZnO. In the transmittance spectra, there is ob-vious abnormal absorbability in near ultraviolet and visible area. Being consist with the calculation, the band gap of Zn_1-xCu_xO films decrease with the increasing Cu concentration. Significant reduction of the PL efficiency caused by Cu dopants is seen in PL spectra. The emission in near ultraviolet and visible area is found moves with increasing the Cu concentration, while the location of the main emission peak doesn't move. It is believed that the absorbability and the emission in near ultraviolet and visible area is related to the impurity levels caused by Cu dopants. And the calculation results that the Cu-3d states lie the entry of the forbidden band confirming our standpoint. We hope this study will be helpful for the understanding of optical properties of Cu-doped thin ZnO films.