Crystal structures and optical properties of(Fe, Co)-codoped ZnO thin films

Abstract

The Fe, Co-codoped Zn0.9FexCo0.1-xO (x=0, 0.03, 0.05, 0.07) thin films are fabricated on the glass substrates by sol-gel method. The surface morphologies, crystal structures, elements and optical properties of the films are investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectrum. The XRD results reveal that all the ZnO films are of wurtzite structure. The diffraction peaks of the clusters, oxide or other impurity phase related to Fe and Co are not observed in the samples. This indicates that codoped is beneficial to the improvement on the dispersion of Fe or Co in ZnO. XPS results reveal that Co elements exist as Co2+, Fe elements exist as Fe2+ and Fe3+, but the increase of relative concentration of Fe leads to the increase of Fe3+ content. The ultraviolet emission peak and blue double emission are observed in the PL spectra of all the samples. Compared with the undoped ZnO film, the Co-codoped ZnO film has a blue shift of ultraviolet emission peak of Fe, the unchanged position of the blue double emission peak, and the weakened luminous intensity. Moreover, the green luminescence peak of the doped ZnO film almost disappears. Finally, the luminescence mechanisms of Fe, Co-codoped ZnO films are discussed by combining the microstructures and compositions of the samples.