Cu doping effects on the electronic and optical properties of Cu-doped ZnO thin films fabricated by radio frequency sputtering

The role of Cu in Cu-doped ZnO (ZnO: Cu) thin films, with a nominal composition of Zn1-xCuxO (x=0, 0.02, 0.05 and 0.07) was investigated using X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES) and UV-visible transmittance measurements. The ZnO: Cu thin films showed single phase wurtzite-hexagonal similar to single crystal structure. The XRD peak positions shifted towards higher scattering angle with increasing Cu doping, indicating substitution of Cu atoms at Zn sites. Spectral features of Cu K-edge XANES indicated that the Cu in ZnO: Cu films is the +2 valence state. The average transmittance of ZnO: Cu films in the visible region was >= 85% and red shift in the optical band gap was observed with increasing Cu doping in ZnO. (C) 2012 Elsevier B.V. All rights reserved.