Effect of low temperature vulcanization time on the structure and optical properties of ZnS thin films

The ZnS films were prepared by vulcanizing the sputtered Zn films at 440 degrees C for different vulcanization time. The crystal structure, surface morphology, microscopic defects and optical properties of the samples were measured by XRD, SEM, slow positron beam Doppler broadening spectroscopy and UV-visible spectrophotometer, respectively. The results show that the vulcanization time has significant effect on the crystallinity and optical properties of the samples. As the vulcanization time increases, the crystallinity of the samples will be improved. But excessive vulcanization time makes the sample crystallinity weak. The transmittance of all samples in the visible range is above 60%. The crystallinity of the sample after 6 h vulcanization is the best, and the band gap value is also up to 3.49 eV. The samples form hexagonal ZnS, whose surface free energy is the lower. The effect of grain specific surface area and S vapor atmosphere on grain growth is also discussed. The slow-positron beam Doppler broadening test results intuitively reveal the changes of microscopic defects in the ZnS film, which are consistent with the results of XRD and SEM analysis.