The electrical properties of dislocations in silicon—II: The effects on conductivity

Abstract

Conductivity measurements were made on both n-type and p-type silicon which contained parallel arrays of edge dislocations. The dislocation densities were of the order of 10 6-10 7 per cm 2 and were introduced by plastic deformation at 750°. Measurements parallel and perpendicular to the array show that the conductivity is highly anisotropic, indicating that space charge cylinders surround the dislocation in both material types. These results imply that the dislocation has an acceptor state which is active in n-type material and a donor state which is active in p-type material. In n-type material, the data are consistent with the cylindrical void model of Read if the model is modified to include scattering by the space charge cylinder. For the current parallel to the dislocation this modification results in the electrons within one mean free path of the space charge cylinder having a mobility reduced by 50 per cent at low temperatures and by 80 per cent at high temperatures. In p-type material the data cannot be as easily explained. The data are, however, qualitatively in agreement with the donor band model suggested earlier, if it is assumed that the density of donor states decreases with increasing electron energy.