Electrical Properties of Dislocations in Ge and Si

The occupation statistics of the energy levels which are introduced by dislocations in Ge and Si are carried out taking into account that charged dislocations are a strong perturbation for the energy levels of the valence and the conduction band. The result is a theoretical relation between the line charge of the dislocation and the apparent experimental Fermi energy which is obtained from the number of free carriers. Comparing this relation with Hall effect measurements the position of the neutral dislocation level in the energy gap and the dislocation length per unit volume that is electrically active can be determined. Possible mechanisms for the screening of charged dislocations are discussed. It turns out that former screening models are appropriate only at very low temperatures and that for a wide range of experimental conditions the screening is done by a rearrangement of free carriers.