The acceptor activity of Cu and Ni and their diffusion in germanium have been investigated. Their acting as acceptors as well as recombination centers gives reason to believe that impurity atoms are placed substitutionally in the lattice. However, the value of 10 -5 cm~/sec of the diffusion constant makes it likely that the diffusion goes interstitially. This leads to the concept of an equilibrium existing between substitutional and interstitial atoms. The fact that the diffusivity is dependent on the range of diffusion can be explained qualitatively on the basis of the picture given above.

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