Diffusion of Li in Si at High $T$ and the Isotope Effect

The diffusion rate of Li in Si at high temperatures has been re-investigated using an outdiffusion technique. The resulting $D$ for ${\mathrm{Li}}^7$ is (2.21±0.07)×${10}^{-6\mathrm{}}$ ${\mathrm{cm}}^2$/sec at (800±5)°C and 2.4×${10}^{-5\mathrm{}}$ ${\mathrm{cm}}^2$/sec at (1350±5)°C. If these results are combined with ion drift results, the diffusion constant can be described by $D=(2.5\mathrm{}\pm 0.2)\times {10}^{-3\mathrm{}}\exp [-(0.655\mathrm{}\pm 0.01\left)\frac{e}{\mathrm{kT}}\right]$. The isotopic effect upon the diffusion has been investigated using ${\mathrm{Li}}^6$ and ${\mathrm{Li}}^7$. At 800°C, the value for $\frac{D_{{\mathrm{Li}}^6}}{D_{{\mathrm{Li}}^7}}$ is ${1.07}_5$±0.02, in accordance with the expected inverse dependence on the square root of the mass. The ionic charge of the Li and the atomic mechanism for Li diffusion is discussed in the light of these and other results.