Effect of oxygen deficiency on optical band gap shift in Er-doped ZnO thin films

Er-doped ZnO films were deposited by reactive magnetron sputtering technique at different oxygen flow rate. The microstructures, the chemical state of the oxygen and the optical absorption properties of ZnO:Er films were investigated. The X-ray diffraction spectroscopy (XRD) results and the X-ray photoelectron spectroscopy (XPS) analyses about the oxygen in the doped samples indicated that oxygen flow rate has great effect on the crystalline quality of ZnO:Er films. It was concluded that the decrease of the crystalline quality of the samples was caused by the oxygen deficiency. The optical absorption properties and the shift of the optical band gaps were investigated. The analysis reveals that the blue shift of the band gaps was caused due to the decreasing of O2−ions at the intrinsic sites and the increasing of O2-ions at the oxygen deficient regions.