Effect of different annealing conditions on the properties of chemically deposited ZnS thin films on ITO coated glass substrates

Abstract

The effects of different annealing conditions such as atmospheres, temperatures and times on the structural, morphological and optical properties of ZnS thin films prepared on ITO coated glass substrates by chemical bath deposition were studied. Aqueous solutions of zinc acetate and thiourea were used as precursors along with stable complexing agents, such as Na(2)EDTA and Na(3)-citrate, in an alkaline medium. X-ray diffraction patterns showed that the as-deposited and as-annealed ZnS films had an amorphous structure or poor crystallinity below the optimized annealing conditions of 500 degrees C and 60 min with the exception of the films annealed in N(2) + H(2)S annealing atmosphere. The ZnS thin films annealed in N(2) + H(2)S atmosphere for 1 h at 500 degrees C showed three sharp peaks for the (1 1 1), (2 2 0) and (1 1 3) planes of polycrystalline cubic ZnS without any unwanted secondary ZnO phases. X-ray photoelectron spectroscopy revealed Zn-OH and Zn-S bonding in the as-deposited ZnS thin film. However, the ZnS thin films annealed at 500 degrees C showed Zn-S bonding regardless of the annealing atmosphere. The sharp absorption edge and band gap energy of the as-deposited and as-annealed ZnS thin films varied from 295 to 310 nm and 3.5 to 3.89 eV, respectively. (C) 2010 Elsevier B.V. All rights reserved.