Electronic structure and optical properties of ZnS/CdS nanoheterostructures

TL;DR

This paper investigates the electronic and optical properties of ZnS/CdS nanoheterostructures using a semi-empirical tight-binding model, providing insights into excitonic states, carrier localization, and optical transition intensities.

Contribution

It applies a symmetry-based, group-theoretical approach combined with configuration-interaction to analyze excitonic properties of ZnS/CdS nanoheterostructures, aligning theoretical results with experimental data.

Findings

Calculated absorption gaps agree with experiments

Predicted enhanced photoluminescence Stokes shifts

Analyzed carrier localization as a function of well thickness

Abstract

The electronic and optical properties of spherical nanoheterostructures are studied within the semi-empirical $sp^{3}s^{*}$ tight-binding model including the spin-orbit interaction. We use a symmetry-based approach previously applied to CdSe and CdTe quantum dots. The complete one-particle spectrum is obtained by using group-theoretical methods. The excitonic eigenstates are then deduced in the configuration-interaction approach by fully taking into account the Coulomb direct and exchange interactions. Here we focus on ZnS/CdS, ZnS/CdS/ZnS and CdS/ZnS nanocrystals with particular emphasis on recently reported experimental data. The degree of carrier localization in the CdS well layer is analyzed as a function of its thickness. We compute the excitonic fine structure, i.e., the relative intensities of low-energy optical transitions. The calculated values of the absorption gap show a good agreement with the experimental ones. Enhanced resonant photoluminescence Stokes shifts are predicted.