Effect of [Zn]/[S] ratios on the properties of chemical bath deposited zinc sulfide thin films |
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Authors: | ZQ Li |
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Institution: | Engineering Research Center for Nanophotonics and Advanced Instrument, Ministry of Education, Department of Physics, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, PR China |
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Abstract: | ZnS thin films have been prepared by chemical bath deposition (CBD) technique onto glass substrates deposited at about 80 °C using aqueous solution of zinc sulfate hepta-hydrate, ammonium sulfate, thiourea, ammonia and hydrazine hydrate. Ammonia and hydrazine hydrate were used as complexing agents. The influence of the ratio of Zn]/S] on formation and properties of ZnS thin films has been investigated. The ratio of Zn]/S] was changed from 3:1 to 1:9 by varying volumes and/or concentrations of zinc sulfate hepta-hydrate and thiourea in the deposition solution. The structural and morphological characteristics of films have been investigated by X-ray diffraction (XRD), scanning electron microscope and UV-vis spectroscopic analysis. ZnS films were obtained with the Zn]/S] ratio ranged from1:1 to 1:6. In the cases of Zn]/S] ratio ≥ 3:1 or ≤1:9, no deposition was found. Transparent and polycrystalline ZnS film was obtained with pure-wurtzite structure at the S]/Zn] ratio of 1:6. The related formation mechanisms of CBD ZnS are discussed. The deposited ZnS films show good optical transmission (80-90%) in the visible region and the band gap is found to be in the range of 3.65-3.74 eV. The result is useful to further develop the CBD ZnS technology. |
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Keywords: | ZnS thin films Chemical bath deposition (CBD) Band gap Optical properties |
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