Cancelation Theorem for Isoelectronic Impurity Binding Energies

Substitutional impurities in undeformed covalent crystals theoretically generate localized states with binding energies of order 1 eV even when the valence of the impurity is equal to that of the atom it has replaced. The weakness of observed binding energies is ascribed to lattice deformations. The observed binding energies are therefore identified as remnants of the original large binding energy.