Structural and optical properties of Co and Ni doped ZnO thin films prepared by RF magnetron sputtering

We have reported the effect of Co and Ni doping on structural and optical properties of ZnO thin films prepared by RF reactive sputtering technique. The composite targets were formed by mixing and pressing of ZnO, Mn3O4, CoO and NiO powders. The thin films were deposited on sapphire, quartz and glass substrates. The structure study confirms the formation of the hexagonal wurtzite ZnO without any secondary phase in transition metal (Co, Ni) - doped samples. Cross-sectional TEM images of all studied samples show a denseand uniformly textured structure composed of column-like structure along the growth direction. The surface morphology of the thin films was studied using atomic force microscopy (AFM). Different surface morphology (AFM) images were obtained depending on the film composition and growth conditions. Optical absorption spectra suggest of substitution Zn2+ ions in ZnO lattice by transition metal atoms. The shift of the absorption edge due to decrease the energy band gap with increasing cobalt content and complex dependence of the energy band gap on content of nickel was observed in optical absorption spectra of the studied films. The room temperature photoluminescence peaks are attributed to near band gap emission and vacancy or defect states.