Dielectric Confinement Effects on the Impurity and Exciton Binding Energies of Silicon Dots Covered with a Silicon Dioxide Layer

The binding energies of hydrogenic impurities and excitons in silicon (Si) dots modelled by a sphere covered with a silicon dioxide (SiO2) layer and embedded in various dielectric media, are calculated as a function of the sphere size and the thickness of the oxide. The strong-confinement limit was considered, so that all of the electrostatic interactions are treated as first-order perturbations considering the confined free-electron state as the unperturbed state. A recently proposed size correction for the dielectric constant of the Si dot is also taken into account. These calculations demonstrate the importance of the image-charge effect due to dielectric discontinuity. In addition, it is shown that the binding energies of the impurities and the excitons inside the silicon dots are greatly affected by alteration of the thickness of the oxides or the surrounding dielectric media.