Theory ofD−states in Ge and Si

Abstract

We present a theory for the $D^{-}$ states in Ge and Si, including the effects of realistic band structures. We obtain binding energies of these states, which are about twice as large as those obtained from using a spherical model. This enhancement in binding is due to the anisotropic, multivalley character of the conduction bands. We predict many bound excited $D^{-}$ states for Ge:Sb and Si:Li. Our binding energies are in substantial disagreement with those obtained in recent submillimeter photoconductivity measurements. This disagreement is attributed to the presence of compensating ($A^{-}$) centers in the sample which interact with the $D^{-}$ center through Coulomb interaction.