Blue shift of optical band gap in Er-doped ZnO thin films deposited by direct current reactive magnetron sputtering technique

Er-doped ZnO films were deposited by direct current co-reactive magnetron sputtering technique and the microstructure and the optical properties of the ZnO films were investigated. XRD analysis reveals that the substrate temperatures have an evident effect on the (0 0 2) preferential orientation and the Er-doped ZnO film deposited at room temperature consists of an amorphous phase. The blue shift of the optical band gap was observed in the ZnO:Er films compared with undoped ZnO film, and the Er-doped ZnO film deposited at room temperature has the largest band gap (about 3.99 eV). The main reason for the broadening of the band gap is attributed to the amorphous phase in the Er-doped ZnO film. Meanwhile, the red shift of the band gap in the ZnO:Er films deposited at high temperature was observed as the crystallinity of the fim became better.