Precipitation of Cu in Ge

Abstract

The kinetics of precipitation of Cu from supersaturated solid solution in Ge have been studied as a function of temperature and dislocation density in the samples. The results can be expressed as an exponential decay with time of the unprecipitated fraction of Cu. We find that for a given dislocation density the time constant for the precipitation has a different temperature-dependence at high temperatures from its temperature-dependence at lower temperatures, and that the temperature of the break in the curve is a function of dislocation density. It is proposed that the high-temperature precipitation is limited by the diffusion of Cu to dislocations by the dissociative mechanism described by Frank and Turnbull. At lower temperatures the rate-limiting step is believed to be the actual process of dissociation of a substitutional Cu into a vacancy and an interstitial Cu atom. The measurements permit an estimate of the vacancy concentration in Ge at ∼715°C.