  The ground-state energy and fine-structure splitting of ionized shallow donor
impurity-exciton complex in quantum dots are investigated. It is found that
fine-structure splitting could be largely reduced by the off-center ionized
impurities since the anisotropic shape of exciton envelope function is
significantly changed. Anomalous Stark shifts of the ground-state energy and
efficient tuning of the fine-structure splitting by the external electric field
due to the local electric field produced by the ionized impurities are
discussed. The scheme may be useful for the design of the quantum dots-based
entangled-photon source.
