Diffusivity and Solubility of Copper in Germanium

The diffusivity and solubility of Cu in Ge have been investigated as a function of temperature in the temperature range 700^∘{}-900^∘{}C, both by resistivity and radio-activity methods. The average diffusivity is 2.8±{}0.3×{}10^-5 cm²/sec in this temperature interval. The solubility shows a maximum of 4.0×{}10¹⁶ atoms of copper cm^-3 at about 875^∘{}C. The precision is not sufficient to determine an activation energy for diffusion. However, calculations based upon a theory of Wert and Zener, indicate an activation energy of about 4000 cal. The "thermal conversion" effect in Ge is explained by a temperature-dependent solution and precipitation of Cu. It is suggested that the acceptor and diffusional properties of Cu in Ge can be accounted for by decreased electron affinity of Cu at higher temperatures.