Effective mass modeling of excitons in type-II quantum dot heterostructures

We present a study of CdTe/CdSe and CdSe/CdTe type-II core-shell nanocrystals using a (2,6)-band effective mass approximation for quantum-dot heterostructures and map the exciton properties as a function of core radius and shell thickness. The Coulomb interaction (including the effects of dielectric mismatch) is calculated in first-order perturbation theory, and optical absorption wavelengths of the two structures are compared. We find that the (2,6)-band theory allows us to identify higher exciton states in absorption data for CdTe/CdSe which a single-band theory does not, thereby demonstrating the importance of an accurate description of the nanocrystal valence band structure. Excitation probabilities are significantly lower and the number of allowed transitions greater in the (2,6)-band theory due to s-d mixing in the hole wave functions.