Optical properties and layer microstructure of CdS films obtained from an ammonia-free chemical bath deposition process

In this work we report the optical and structural properties of chemically deposited CdS films obtained from an ammonia-free chemical bath deposition process. The deposition process is based in the substitution of ammonia by sodium citrate as the complexing agent in the reaction solution. We applied spectroscopic ellipsometry and optical transmission and reflection spectroscopy to determine the thickness, optical constants and energy band gap of a set of CdS samples obtained by this process at different deposition times. Additionally, the spectroscopic ellipsometry analysis provided information about the microstructure and kinetic growth process of the CdS films. We found that experimental data fit quite well with a model of two different layers, corresponding to different growing stages, to simulate the CdS films. The first layer, formed at the earlier growing stages by means of the ion by ion deposition process, was assigned to a pure compact CdS layer and their optical properties were simulated by a Kramers–Kronig consistent model. The second external layer composed by a mixture of CdS and voids was modeled by the Bruggeman effective medium approximation. The results were compared to those obtained for a set of CdS samples obtained from a deposition process which employs ammonia in the reaction solution.