Zinc sulphide (ZnS) thin films were synthesised by chemical bath deposition technique without using complexing agent. A physicochemical study was realized on the growth solution composed of ZnCl 2 , KOH, and SC(NH 2 ) 2 . The bath solution was at 60°C and pH values of 11.5, 12, and 12.5 were selected for growing the material. The species distribution diagrams, and solubility curves show that the growth mechanism requires the presence of zinchydroxide ions, and alkaline pH for growing the ZnS. The physicochemical properties of the samples improve as the pH of the solution increases. Samples deposited at pH=12.5 present a cubic structure (sphalerite) and bandgap energy of 3.72 eV, consistent with bulk-ZnS. For comparison, additional chemical baths were prepared by using NH3 as complexing agent; however, the properties of those samples result inferior. This methodology was validated by depositing ZnS films at 40°C without the complexing agent, obtaining similar results.

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The material deposition in aqueous solution, also known as chemical bath deposition (CBD), is a well-established technique for the fabrication of semiconducting thin films. The success of the CBD technique is mainly based on the relatively easy implementation and operation requirements. The CBD has importantly contributed to the development of sensors, optical devices and solar cells applications. In this review, the origins and current state of the art of the CBD technique, the involved physicochemical processes, the growing mechanisms, and the analytical techniques for the estimation of optimal physicochemical conditions for the film deposition are discussed. Emphasis on authors' experience on CBD of CdS, ZnS, Zn (OH) 2 , and ZnO films are here highlighted, following methodologies for a high control of the deposited materials, such as the species distribution diagrams and the solubility curves.