Binding energy of an off-center shallow donor image in a spherical quantum dot

The binding energy of a negatively charged hydrogenic impurity with on- and off-center positions in a spherical Gaussian quantum dot was calculated with the configuration interaction method. Our calculations show that Eb is always positive for on-center impurities with a maximum near to the radius for one-electron stability of the potential well Rc. For off-center positions the binding energy can assume negative values within a range of the quantum dot radius, thus indicating the instability of the system.