Characteristics of Nanocrystalline ZnS thin films grown on glass with different Zn ion concentrations by CBD technique

Abstract

Thin films of zinc sulfide (ZnS) with various values of Zn ions concentrations (0.2,0.3,0.4)M have been prepared by Chemical Bath Deposition Technique on glass slides substrate at 80 oC bath temperature. The prepared films were annealed in air at constant temperature 400 oC and constant time (180) min . Structural and optical properties of ZnS thin films were investigated and analyzed extensively before and after annealing . The structure properties of the prepared films were studied by using x-ray diffraction technique , it has been found that all prepared films at different Zn ions concentrations were amorphous structure, while the annealed films showed polycrystalline structure type (Hexagonal) , The lattice constants (a , c) of ZnS films were calculated and its values found about (3.86,31.6) A , the crystallite size (Grain size) of ZnS thin films also calculated and found to vary from (20.8 to 83.7) nm ,which indicate that annealed ZnS thin films has Nanocrystalline structure . The optical properties of ZnS thin films contained study of transmittance spectrum in the range of wave length (190-1100)nm by using UV- ViS. Spectrophotometer was carried out. Transmittance decreased with increasing the Zn ions concentrations of ZnS films , also the transmittance decreased after annealing . The fundamental absorption edge of ZnS thin films shifted toward the highest photon energies (blue shift) with increasing the Zn ions concentration and shifted toward the lowest photon energies (red shift) after annealing. The absorption coefficient values which calculated from the absorbance spectrum was larger than 10 4 cm -1 gives an indicate that ZnS films were direct semiconductors and the electronic transitions was a direct transitions. The optical energy gap values for allowed direct transition found in the range of , (1.594-3.060) eV for (ZnS) thin films with (0.2 - 0.4 M) Zn ions concentration and in the range of (3.215-3.099) eV for the same concentrations after annealing. Keyword: ZnS , thin film ,CBD, structural and optical properties.