Tight-binding analysis of the structural dimension dependence of the optical bandgap in ZnSe/ZnS core-shell quantum dots

The structural dimension dependence of the optical bandgap in ZnSe/ZnS core–shell quantum dots is examined using a valence force field model combined with an atomistic tight-binding approach. We demonstrate that increasing shell thickness enhances compressive strain within the ZnSe core, resulting in bandgap widening. Simultaneously, wavefunction penetration into the ZnS shell mitigates quantum confinement, thereby narrowing the bandgap. The overall response of the optical bandgap to core diameter and shell thickness is, thus, governed by the competition between strain-induced widening and penetration-induced reduction. By isolating these two contributions, we develop a compact model that accurately reproduces the atomistic calculation results across a broad range of structural dimensions.