Influence of Selective Nucleation on the One Step Chemical Bath Deposition of CdS/ZnO and CdS/ZnS Composite Films

We show how the composition and the morphology of composite films deposited by one step chemical bath deposition (CBD) can he controlled by varying kinetic factors, in particular by selective nucleation, as well as varying the rate of growth of specific phases'. ZnS/CdS composite films are obtained from a solution containing a mixture of Zn and Cd salts and thiourea under conditions where nucleation of zinc oxide is not favorable, while CdS/ZnO films grow if ZnO nucleation is promoted. In the absence of Cd in the deposition solution, only ZnS forms under all the conditions used by us. The role of Cd in directing the deposition to ZnO is believed to be due to the higher affinity of Cd for S compared to Zn, therefore preventing formation of ZnS in the early stages of deposition and allowing ZnO to nucleate. This demonstrates the importance of interaction between the various components in the solution. Addition of ethanol to the deposition solution, believed to serve as a dehydrating-assisting agent for Zn(OH)(2), had a crucial role on the deposition outcome by accelerating formation of ZnO in the bulk of the solution, and leading to more rapid depletion of Zn with respect to Cd.