Interdependence of Ar and O2 partial pressure on the properties of RF sputtered Zn0.85Mg0.15O thin film

Band gap engineering of zinc oxide (ZnO) has gain substantial interest from past few years. Assimilation of Mg in ZnO increases band gap from 3.37 eV to 4.1 eV and it has versatile application in short wavelength UV devices. In this work, we have studied influence of growth ambient on RF sputtered Zn_1−xMg_xO (x = 15%) thin films. Here, we have deposited Zn_1−xMg_xO films at varying Ar/(O₂) gas ratio from 4:1, 3:2, 2:3, 1:4 and 0:5 in growth ambient which yielded sample A, B, C, D and E, respectively. As the O₂ content in chamber decreases, (i.e. sample A), the surface recombination of O₂ atoms in the horizontal direction reduces as compared to that of Zn²⁺ and Mg²⁺. Hence, we observed (100) orientation peak along with (002) in High resolution X-ray diffraction pattern. Reduction in full width half maximum values of the (002) peak were observed from sample A to E which suggests reduction in the Mg concentration. Photoluminescence measurement demonstrated the growth of films in Ar-rich ambient (A) lead to the formation of oxygen vacancies whereas reducing it results in grain size reduction, grain boundary–related defects formation and lower Mg concentration. X-ray photoelectron spectroscopy(XPS) spectra confirmed the reduction in oxygen vacancy peaks with increase in the oxygen concentration in the growth ambient. To summarize, Zn_1−xMg_xO film grown in 3:2 ratios of Ar/O₂ ambient yielded superior quality with minimal defect states using RF sputtering technique.