Influence of Ag Dopant Content on Structural and Optical Energy Gap of Zns Thin Films Deposited By Spray Pyrolysis Technique

Abstract

In this study, pure and Ag doped ZnS thin films were prepared onto glass substrates using spray pyrolysis deposition (SPD) method. 0.1 M and 0.2 M of zinc chloride ZnCl2, thiourea (NH2) 2 CS and 0.1 M of silver nitrite Ag (NO3) 2 as a source of Zn, S and Ag respectively. The spray deposition parameters was kept at nozzle – substrate distance 30 ± 1 cm, air pressure 1 mbar, spray time 3 minute and substrate temperature was 450 oC. Structural and optical properties have been studied using x-ray diffraction technique in the diffraction angle rang (20-50) o and UV-Vis spectrophotometer in the wavelength range (300-800) nm. The effect of Ag dopant content on the structure parameters such as crystallite size and lattice constants (a, c) and on the optical transmittance, absorbance and forbidden energy gap were investigated. XRD measurements demonstrated that ZnS thin films had polycrystalline structure with hexagonal phase. The average crystallite size was increased from (16.63 nm to 37.80 nm) by increasing Ag concentration from pure to 8% Ag while the dislocationdensity and the strain decrease with increase of dopant concentration due to enhancement of crystallinity. In the ultraviolet region, the optical transmittance of these films with changing of dopant concentrations of silver was observed to be more than (92%) and the optical absorption edge shifted toward lower wavelengths "blue shift". The value of energy band gap of ZnS films was found to be at (3.02, 2.91, 3 and 3.15) eV with (0, 4, 6 and 8) % of silver dopant concentration, the broadening of the band gap was due to Burstein–Möss effect. From these results it can be conclude that the fabricated ZnS: Ag thin films was suitable for solar cells, optical coating and blue LED applications.