The electrical properties of dislocations in silicon—I: The effects on carrier lifetime

Abstract

Lifetime measurements were made on both n-type and p-type silicon which contained dislocation densities of the order of 10 7 per cm 2. The dislocations were introduced by plastic deformation at 750°. A theory for transient recombination, based on R ead's hypothesis of a potential barrier at the dislocation, is developed to explain the experimental data. The theory and the measurements show that the potential barrier inhibits the capture of majority carriers causing long lifetimes to be observed. Also, it is shown that for small excess carrier densities, the lifetime is independent of the dislocation density and only weakly dependent on the majority carrier density. An analysis of the data in n-type silicon reveals that the dislocation has an acceptor level which is approximately 0.52 eV below the conduction band, and which has a capture cross section for electrons of approximately 10 −15 cm 2. In p-type silicon the dislocation is found to have a donor level whose location is not as well defined. The donor state was measured at 0.50 eV, 0.42 eV and 0.38 eV above the valence band in 200 Ω-cm, 50 Ω-cm, and 10 Ω-cm material respectively. The donor state's capture cross section for holes is about 10 −16 cm 2 for all three resistivities. It is suggested that in p-type material the donor states lie in a band rather than at a discrete level.