Exciton fine structure in semiconductor nanocrystals in the tight‐binding method

Abstract

We present a symmetry-based tight-binding (TB) method for calculating the exciton states and optical spectra in spherical semiconductor quantum dots (QD's). Here we focus on the resonant photoluminescence (PL) Stokes shift between the first optically active level and the “dark” exciton ground state for nanocrystals (NC's). The method has so far been applied to CdSe and CdTe NC of diameter up to 6 nm. The experimental gaps and Stokes shifts show satisfactory agreement with the theoretical results. We have also investigated two series of quantum dot quantum wells (QDQW's). One of them is based on CdS cores which act as energy barrier; HgS well layers are intercalated between the core an additional CdS clad. The second serie of QDQW's is based on ZnS cores and CdS layers as wells. The experimental absorbance edges in the latter are quantitatively reproduced by our model which allows us to confidently predict the corresponding Stokes shifts.