The effect of Mg and Al co-doping on the structural and photoelectric properties of ZnO thin film

Mg-Al co-doped ZnO thin films were prepared via radio-frequency reactive magnetron sputtering technique. X-ray diffraction investigation showed all the thin films with different Mg:Al ratio had hexagonal wurtzite structure. All the thin films showed (100) preferential orientation of ZnO. When Al concentration was kept constant but Mg concentration was increased, the grain size decreased at first and then increased. When Mg:Al ratio was 3:1, the grain size reached a maximum. Ultraviolet-visible spectra showed the thin films had a high average transmittance of 80% in the visible range. The optical band gaps of the thin films were obtained as follows: 3.31, 3.32, and 3.37 eV, corresponding to the Mg:Al ratio of 0:1, 1:1, and 3:1, respectively. Photoluminescence spectroscopy showed all the thin films had four main peaks located at 386, 410, 463, and 499 nm. The origin of blue peak is oxygen vacancy. When Mg concentration was kept constant but Al concentration was increased, I-V curve presented that for both of the heterojunctions the rectifying behavior was formed. The conductivity of Mg:Al=1:1 thin film is higher than that of Mg:Al=1:0 thin film. After illumination, light I-V curve deviated from rectifying character.