Polaron effect onD−centers in weakly polar semiconductors

The polaron correction to the energy of the two-electron bound ${(D}^{-})$ states of a shallow donor in weakly polar semiconductors is calculated. Both upper and lower bounds to the energy shift of the ground state and also to the $D^{-}$ transition energy are derived within second-order perturbation theory. The results show a stronger polaron effect in these systems than for two independent single-electron systems. The polaron correction to the $D^{-}$ level depends strongly on the properties of the electron-phonon interaction and/or the relative position of the two electrons.