Influence of Copper Content on Structural and Optical Properties of Cu2(x)Zn(1-x)S Thin Films

Cu2 (x) Zn (1-x) S alloy was synthesized by reacting high purity elements Cu, Zn, and S with ratios of Cu x= (0.0), (0.25), (0.50), (0.75) and (1.0) in an evacuated quartz ampoule. Cu2 (x) Zn (1-x) S thin films have been prepared by vacuum thermal evaporation method from the Cu2 (x) Zn (1-x) S alloy. The thin films were deposited onto glass substrates under vacuum pressure of 10-5 torr with thickness of 500 nm. The analysis of structural and optical properties of the Cu2 (x) Zn (1-x) S thin films were carried out by X-ray diffraction (XRD) and UV-Vis Spectrophotometer. The X-Ray diffraction method was utilized to test the Cu2 (x) Zn (1-x) S film. It was found that the films had a polycrystalline structure with cubic phase and that the average crystal size varied from (253) A0 to (348) A0. The study of the optical properties were carried out within a range of wavelength between (200nm) and (1100nm). The average transmission of the films was about (70-90) %. It was decreasing with the increasing of copper concentration (x). The value of absorbance was very dependent on copper concentration in thin films as the absorbance was proportional with the increase in copper concentrate. The absorption coefficient () and optical energy gap were measured for direct electronic transitions. And the film energy band gap was in the range of (3.10-2.08) eV, depending on the material of the thin film and the concentration of copper. Finally, the extinction coefficient, refractive index and dielectric constant were measured for all thin films. The refractive index and dielectric constant, at first, increased with the increase of wavelenght and reached the largest possible value and then they decreased with the increase of wavelenght. The refractive index varied between (1.2) and (2.6).