Characterization of Nanostructured ZnS Thin Films Deposited by Chemical Process on the Si Substrates

Recently, ZnS thin films have attracted interests because of their application in thin film solar cells, optical coatings, optoelectronics appliances such as electroluminescent, photoconductor and especially photovoltaic devices and light emitting diodes [1]. ZnS is an important semiconductor material with a large band gap (Eg = 3.6 eV), with a vast potential applications in thin film devices [2]. Various techniques, such as atomic layer deposition (ALD),electrochemical deposition (ED), chemical vapor deposition (CVD), successive ionic layers adsorption and reaction (SILAR), photochemical deposition (PD), chemical deposition (CD), molecular beam epitaxy (MBE) and spray pyrolysis have been employed to prepare ZnS thin film. Among them, the CD method is more attractive because of its simplicity [3]. The main advantages of the CD method are low cost, room temperature process and easy coating of large surfaces. This technique does not require expensive apparatuses. CD is a technique in which thin films are deposited on to substrates immersed in dilute solutions containing metal ions and the sulfide ions. In addition, this method is free of many inherent problems associated with high-temperature process which might cause some problems such as increasing in point defects, concentrations, evaporation and decomposition of ZnS thin films [4,5]. The chemical deposition process uses a controlled chemical reaction to deposit a thin film by precipitation. This technology is based on controlled release of the metal ions and sulfide ions. In this paper we are report preparation of nanocrystalline zinc sulfide thin films onto n-type Si substrates using a weak acidic bath at 70 °C for 4 hours. In this work zinc acetate acts as source of zinc ions, TAA acts as source of sulfide ions, and ethylenediamine acts as complexing agent for zinc ions.