Mechanism of Diffusion of Copper in Germanium

To explain the rapid diffusivity of copper in germanium and its dependence on structure, it is proposed that the copper be dissolved in two states, interstitial and substitutional. It is deduced that in the interstitial state the solubility of copper is about ${10}^{-2\mathrm{}}$ times less and the diffusivity many orders of magnitude greater than in the substitutional state. Conversion from the interstitial to the substitutional state is effected by lattice vacancies which are generated at free surfaces and dislocations; this accounts for the structure dependence of the diffusivity observed by Tweet and Gallagher.