Microstructure, Surface Morphology And Optical Properties Of Cu-doped ZnO Thin Films Prepared By Magnetron Co-sputtering

As a new transparent conductive oxide film material, ZnO is applied extensively infield of solar cell and optoelectronic devices, because of large wide-band gap (3.37eV),large exciton binding energy (60meV), availablity to doping, cheapness, nontoxicity andinnocuousness. Among various dopants, Cu doping can modify the luminescence and theabsorption coefficient of ZnO crystals through reducing the band gap.Most previous researchers studied ZnO:Cu films with moderate doping level. In thisstudy, we prepare two groups of ZnO:Cu films with different Cu doping content (0-23.8%)on grass substrates by magnetron co-sputtering. The influence of Cu concentration on themicrostructure, crystal morphology and optical properties of the ZnO:Cu films had beensystematically investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), the photoluminescence (PL) measurement and ultraviolet visible spectrophotometer(UV-VIS), respectively.XRD and SEM results show that moderate Cu doping can enhance the crystallinity ofthe films, whereas heavy doping inhabits it. Cu doping has a significant fluorescencequenching effect. It was found that all the visible emissions peaks corresponded to blueemission. The blue emissions peaks were mainly originated from the transition from theconduction band bottom to Zinc vacancy and the transition from antisite Zinc to zincvacancy. We can control the intensity of blue emissions peaks by changing the Cu dopingcontent.The UV-Vis results of heavily doped samples show that Cu dopant significantlychanges the absorption characteristics of films in the near ultraviolet and visible range.With the Cu content increasing, the intensity of absorption peak increases gradually, and thered shift phenomenon appeared. The band gap narrowing effect of ZnO films increasesgradually with increasing Cu-content. A promising band gap reduction of0.64eV wasachieved at23.8%doping level.