Impurity states and photoionization cross section in CdSe/ZnS core–shell nanodots with dielectric confinement

The effects of the electric field and impurity position on the ground and lowest excited states of a hydrogenic donor in the core–shell CdSe/ZnS quantum dot are studied within the effective mass approximation, taking into account the polarization charges at the nanocrystal boundary. We found a pronounced redshift of the impurity energy under low dielectric constant environment due to the predominance of the effective Coulomb term over the self-interaction potential. For particular donor positions the resonant peak of the photoionization cross-section is strongly enhanced as a result of the dielectric confinement-induced changes in the electronic states. The tuning of the nanodot optical properties can be also achieved by an applied electric field which allows a red- or blue-shift of the threshold energy for the impurity photoionization.