Study of substrate temperature and copper doping effects on structural, electrical and optical properties of Cu-doped and undoped ZnO thin films

Undoped and Cu-doped ZnO (ZnO:Cu) thin films were prepared using magnetron co-sputtering. Effects of substrate temperature T_s on their structural, electrical and optical properties were comparatively investigated using X-ray diffraction, atom force microscopy, and ultraviolet visible spectrophotometer. ZnO:Cu thin films with different doping content were prepared and studied in order to investigate the effects of Cu-doping content. The results show that all the films exhibit a single phase (002)-oriented hexagonal wurtzite structure. Higher T_s enhances the crystallinity and reduces the compressive stress of the films. Cu-doping and increasing T_s lead to rougher surface and larger granules. The resistivity of both the ZnO and ZnO:Cu films increases with T_s. Interestingly, optical band gap E_g of ZnO:Cu films increases significantly with T_s, while E_g of undoped film is not obviously influenced by T_s. Cu-doping content is an important factor affecting the physical properties of ZnO:Cu thin films. In our experiments, Cu-doping composition sightly decreases with T_s increasing. Cu-doping reduces the resistivity, leads to the red-shift of absorption edge, and narrows E_g of ZnO thin films.