Influence of Fe content on the structural and optical properties of ZnFeS thin films

ZnFeS thin films have been grown on c-plane sapphire substrate using low-pressure metalorganic chemical vapor deposition (LP-MOCVD) equipment. The X-ray diffraction (XRD) patterns indicated that the diffraction peaks positions of ZnFeS thin films shifts gradually towards the lower angle side due to substitution of Zn by Fe atoms in the crystal lattice with increasing Fe content. When gas flow rates of Fe (CO)5 varied from 1 to 6 ml min−1, crystalline phase of the ZnFeS thin film changed from the hexagonal to cubic structure. And when gas flow rates of Fe (CO)5 was less than 6 ml min−1, ZnFeS single-crystal structure was obtained. From the measurements of optical absorption spectrum, the energy gaps of the samples were evidently narrowed with increasing Fe component. The electronic states of ZnFeS were investigated by X-ray photoelectron spectroscopy (XPS). It was found that the S 2p shifted towards higher binding energies side due to the larger bond strength of Fe–S than that of Zn–S, but the Fe incorporated into the ZnS lattice did not affect the Zn 2p core levels.