Field-retarded diffusion of antimony in germanium

Abstract

Diffusion techniques, applied to semiconductors to produce impurity gradients, have revealed that under certain conditions Fick's law is not always obeyed. It will be shown experimentally and theoretically that a field-retarded diffusion of antimony will occur in germanium in the presence of a p-type impurity, e.g. gallium, which is higher in concentration and has a negative gradient in the direction of the donor diffusion. This implies, in addition, temperature settings whereby the intrinsic carrier concentration n i is smaller than N A, the number of ionized p-type impurity atoms. The investigations have been carried out for a temperature range of 700–900°C and with concentration levels of N A ≤ 10 20atoms/cm 3 and of N D ≤ 10 19atoms/cm 3. By including field terms it is shown that the diffusion constant of antimony D Sb is dependent upon the ratio of its concentration N D to the intrinsic carrier concentration n i, and the ratio of acceptor and donor gradients. The experimental evidence is in general agreement with the theoretical formulation.