Electron-hole correlations and optical excitonic gaps in quantum-dot quantum wells: Tight-binding approach

Electron-hole correlation in quantum-dot quantum wells (QDQW’s) is investigated by incorporating Coulomb and exchange interactions into an empirical tight-binding model. Sufficient electron and hole single-particle states close to the band edge are included in the configuration to achieve convergence of the first spin-singlet and triplet excitonic energies within a few meV. Coulomb shifts of about 100 meV and exchange splittings of about 1 meV are found for CdS/HgS/CdS QDQW’s (4.7 nm CdS core diameter, 0.3 nm HgS well width, and 0.3 nm to 1.5 nm CdS clad thickness) that have been characterized experimentally by Weller and co-workers [D. Schooss, A. Mews, A. Eychmüller, H. Weller, Phys. Rev. B, 49, 17 072 (1994)]. The optical excitonic gaps calculated for those QDQW’s are in good agreement with the experiment.