Composition of RF-sputtered ZnS films

Rutherford back-scattering and X-ray photoelectron spectroscopy (XPS) have been used to study the stoichiometry and chemical composition of RF-sputtered thin films of ZnS. The results show that stoichiometry of the starting material is no guarantee of stoichiometry in the final film. Films grown in the normal way have a high oxygen content and a Zn/S ratio much greater than unity. XPS shows these films to be a ZnO+ZnS mixture. To obtain low oxygen content and good stoichiometry a good starting vacuum and high throughput of sputtering gas (argon) are necessary.