Band gap analysis for nanometric sputtered CdTe and CdS films

The phenomenon of band gap widening, attributed to quantum confinement resulting from films' thinning, is of significant interest in the photovoltaic field. Specifically, changes in CdTe and CdS band gaps are important in band engineering to facilitate devices coupling. Therefore, in this study, the sputtering technique is employed to deposit both materials with varying thicknesses within the 10-405 nm range. Structural and optical properties as functions of film thickness were assessed, and the band gap was determined through the Brus and absorption spectrum fitting (ASF) methods to compare it. Brus and ASF methods, demonstrated how the band gap changes with varying film thickness for both materials. However, a noticeable shift was observed between the methods in their respective curves. An explanation for this shift, and a new model correlating the reduction in film thickness with optical band gap widening is provided. This model constitutes the primary contribution of this paper.