Modeling thin film CdS development in a chemical bath deposition process

The chemical bath deposition (CBD) process is currently favored for the preparation of CdS thin films of commercial interest. A chemical engineering type analysis of the CBD process is carried out in this paper to aid its design and optimization. Model equations are developed (based on a population balance formulation) for the temporal variation of reactant concentrations as well as of the solid phase, both in the bulk and on the substrate. A possible sequence of elementary mechanisms (i.e., nucleation, surface reaction, etc.) is suggested, and the resulting comprehensive model is solved numerically. Computational results show that the model is consistent with available experimental data on film thickness evolution. Furthermore, the influence of the process parameters on the results is studied theoretically and discussed extensively for several cases. The model may prove very useful for optimization of the CBD process with respect to its design variables (reactant concentrations, process time, etc.) as well as for efficient experimental determination of presently uncertain or missing parameter values.