Effect of diffusion on the formation of chemically deposited films of CdS and other chalcogenides

•Observed square root dependence of the film thickness against of deposition time.•The maximum size of a particle participating in the upward mass transfer is 1000 Å.•It is shown that growth rate of a film can be increased by reducing the boundary layer.•The shape of the deposited islands is obtained from optical transmission spectra.•The contact angle for the films CdS, ZnS, InSe and glass substrate is determined. Chemical bath deposition has been used as a method to synthesize metal chalcogenide thin films. This method is being intensively studied, since chalcogenide films demonstrate an applied significance. Traditionally, the mechanism of this film growth is investigated by kinetic analysis. The role of diffusion processes, taking part in film formation, is much less investigated. In this paper the film growth is interpreted in terms of diffusion- and reaction-limited processes. Employing this approach, we consider the possibility of occurrence of the upward vertical diffusion for the Brownian particles towards the substrate working side and establish the maximum particle size. We propose and demonstrate the applicability of a method for determining the size and shape of islands of discontinuous ZnS, CdS and InSe films. The square root dependence of the continuous CdS film thickness as a function of the deposition time is experimentally confirmed for certain ammonia based solutions. Finally, we present results for the effect of immersion depth in case of diffusion limitation of the growth rate on the film thickness. The derived theoretical dependence on the depth is consistent with the experiment for the cadmium sulfide films deposited from the citrate solution.