Diffusion of silver, cobalt and iron in germanium∗

Abstract

Diffusion of Ag, Co and Fe in Ge are investigated by radiotracer techniques. We found that: (1) In most cases, the concentration varies as exp(− x/ L) rather than the Gaussian or the error function as usually expected from Fick's (second) law. (2) The diffusivities of these elements in Ge are in the range of 10 −6–10 −7 cm 2/sec at temperatures around 800°C. The values are higher in low dislocation (less than 10 3 pits/cm 2) than in high dislocation (around 10 5 pits/cm 2) crystals. (3) The solubilities of Ag, Co and Fe in Ge are very low, in the range of 10 −8–10 −9 in atomic fraction. (4) The activation energy of Co diffusion in Ge is about 1 eV, nearly the same as those of Ag, Ni and Fe diffusion as obtained by other workers. It is suggested that the anomalous diffusion is due to a double stream process which is composed of free species and trapped ones. This trapping mechanism not only leads to a concentration varying approximately as exp (− x/ L) but also offers reasonable explanations for many other experimental facts.