Structural, optical and chemical analysis of zinc sulfide thin film deposited by RF-mganetron sputtering and post deposition annealing

Zinc sulfide (ZnS) thin films were deposited by radio-frequency (RF) magnetron sputtering. The effects of the process parameters such as deposition time and RF-power, as well as of post deposition annealing under oxygen containing atmospheres, on the material properties of ZnS films have been investigated. X-ray diffraction analysis reveals out that the as-deposited ZnS films preferred (002) hexagonal wurtzite and (111) cubic zinc blend (111) at 28.60°, while a thicker ZnS film has additional hexagonal wurtzite (100), (110), and (200) planes coexisting with the preferred oriented-planes, suggesting that the thickness is dependent on the growth of ZnS. After annealing, ZnO phases were detected, indicating island-like grain growth on the surface of the ZnS film. By increasing the deposition time and the RF power, the optical band gap energy (Eg) of the ZnS film changes from 4.13 to 3.87 eV, indicating the presence of lower Eg with thicker ZnS film. The lower Eg (∼3.27 eV) value of the annealed films is attributed to the ZnO transition. Unlike bulk ZnS material (Zn/S∼1.08), deposited ZnS thin film has Zn-rich and S-deficient composition (Zn/S∼1.28). However, the Zn/S ratio is closer to the ideal value when there is a longer deposition time or higher RF-power.