Mobility of Impurity Ions in Germanium and Silicon

Lithium has been shown to migrate as a singly-charged positive ion in single crystals of both Ge and Si in temperature ranges of 150-600^∘{}C and 360-860^∘{}C, respectively. The mobility of the Li⁺ in crystalline Ge and Si has been measured as a function of temperature. Through the use of the Einstein relation between diffusion constant and mobility, values of the diffusion constants in cm²/sec of Li⁺ in Ge and Si are obtained as follows: D=25×10^-4exp(-11800)RT for Ge and D=23×10^-4exp(-15200)RT for Si, in satisfactory agreement with previously published results on the thermal diffusion of Li⁺. A curious reversion of conductivity type of solid solutions of Li in Ge is discussed. Copper has likewise been found to move as a positive ion in germanium in the temperature range 800^∘{}-900^∘{}C leading to diffusivities in agreement with previously published results.