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

Abstract

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 28.60A degrees, 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 (E-g) of the ZnS film changes from 4.13 to 3.87 eV, indicating the presence of lower E-g with thicker ZnS film. The lower E-g (similar to 3.27 eV) value of the annealed films is attributed to the ZnO transition. Unlike bulk ZnS material (Zn/S similar to 1.08), deposited ZnS thin film has Zn-rich and S-deficient composition (Zn/S similar to 1.28). However, the Zn/S ratio is closer to the ideal value when there is a longer deposition time or higher RF-power.