Effect of four different zinc salts and annealing treatment on growth, structural, mechanical and optical properties of nanocrystalline ZnS thin films by chemical bath deposition

ZnS thin films were deposited from four different zinc salts on glass substrates by chemical bath deposition method. Different anions of zinc salts affect the deposition mechanism and growth rate, which influence the properties of the films significantly. The ZnS thin film deposited from ZnSO4 is smoother, thicker, more homogeneous and compact, nearly stoichiometric, comparing with the films deposited from Zn(CH3COO)2 and Zn(NO3)2, and ZnCl2. The scratch test of bonding force between ZnS film and substrate shows that the ZnS film deposited from ZnSO4 has the most excellent adhesion with the substrate. The presence of SO42− promotes heterogeneous ZnS thin film growth via ions by ions deposition, and the films deposited from Zn(CH3COO)2 and Zn(NO3)2 are formed via clusters by clusters deposition. XRD and HRTEM results show that cubic ZnS films are obtained after single deposition, and the grain size of ZnS thin film deposited from ZnSO4 for 2.5 h is 10 nm. The average transmission of all films is greater than 85% in the wavelength ranging from 600 to 1100 nm, and the transmission of films deposited from ZnSO4 or Zn(NO3)2 for 1.5, 2 and 2.5 h is greater than 85% in the wavelength varying from 340 to 600 nm, which can enhance the blue response. The band gaps of all ZnS thin films are in the range of 3.88–3.99 eV. After annealing treatment, the mechanical and optical properties of the ZnS thin film deposited from ZnSO4 are improved significantly.