The topological interaction of impurities with dislocations was studied theoretically, and it was found that this interaction reduced the binding energies of carriers to Coulombic impurities, for off-center valleys in semiconductors, by more than a factor of 2 in the case of an isotropic carrier mass, and by a factor of 4 in the case of highly anisotropic valleys.

Topological Interaction of Coulombic Impurity Centers with Dislocations in Semiconductors. Y.T.Rebane, J.W.Steeds: Physical Review Letters, 1995, 75[20], 3716-9