Physicochemical Conditions for ZnS Films Deposited by Chemical Bath

Abstract

© 2014 The Electrochemical Society. All rights reserved. A physicochemical analysis on the chemical bath deposition technique (CBD) used for ZnS films deposition is discussed. Based on species present in solution and solubility diagrams, CBD-ZnS films experimental conditions are proposed at 80°C by keeping fixed the ZnCl2 and thiourea (SC(NH2)2) concentrations and by using different ones of NH4NO3 and KOH used for the bath, to obtain different pH values. Better conditions were experimentally obtained for synthesizing ZnS thin films with high optical quality and good crystalline orientation. These better conditions produced ZnS films with bandgap energy of 3.73 eV and film thickness about 100 nm. It was observed that the crystalline structure of the deposited films depend strongly on the physicochemical conditions, giving a blenda-cubic structure with (111) as preferential orientation. However, additional diffraction peaks of ZnO and Zn(OH)2 were observed on films deposited far from the better conditions. The surface roughness of the films ranged between 2.2 to 12.6 nm as obtained from atomic force microscopy images. XPS analysis on films surface confirms that excess of O concentrations affects the crystalline structure and the optical quality. Stoichiometry of the CBD-ZnS films was measured through [S]/[Zn] ratio and was found to be between 0.5 and 0.57.