Erbium concentration effects on the structural and photoluminescence properties of ZnO:Er films

Films of Er-doped ZnO (ZnO:Er) were prepared on MgO(100) wafers by ultrasonic spray pyrolysis at 550 °C. The concentration of Er in the deposition source varied from 1.0 to 3.0 wt.%. The crystallographic properties and surface morphologies of the films were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Polycrystalline films were grown with a dominant direction of [002]. The grain size of the films was reduced by Er-doping. The ultraviolet (UV) photoluminescence properties of the films as a function of Er concentration were studied at low temperature (18 K) and room temperature (300 K). In undoped ZnO films, UV peaks at 3.375 and 3.360 eV were observed at 18 K, which are considered to be due to free excitons and donor-bound excitons, respectively. The peaks from the free exciton transitions disappeared at room temperature. Er-doping enhanced the room temperature UV emission of ZnO:Er films. ZnO:Er (2.0 wt.%) films prepared from the deposition source including 2.0 wt.% Er showed UV peaks which were ∼ 15 times stronger than those of undoped ZnO films.