Evaluation of the dielectric function of colloidal Cd_{1 − x}Hg_xTe quantum dot films by spectroscopic ellipsometry

We report on the investigation by spectroscopic ellipsometry of films containing Cd_1−xHg_xTe alloy quan-tum dots (QDs). The alloy QDs were fabricated from colloidal CdTe QDs grown by an aqueous synthesis process followed by an ion-exchange step in which Hg²⁺ ions progressively replace Cd²⁺. For ellipso-metric studies, several films were prepared on glass substrates using layer-by-layer (LBL) deposition. The contribution of the QDs to the measured ellipsometric spectra is extracted from a multi-sample, transmission and multi- angle-of-incidence ellipsometric data analysis fitted using standard multilayer and effective medium models that include surface roughness effects, modeled by an effective medium approximation. The relationship of the dielectric function of the QDs retrieved from these studies to that of the corresponding II–VI bulk material counterparts is presented and discussed.