Silicon Self-Diffusion in Isotope Heterostructures

Self-diffusion of silicon is measured between 855 and 1388 \ifmmode^\circ\else\textdegree\fi{}C in highly isotopically enriched ${}^{28}\mathrm{Si}$ layers. The profiles of ${}^{29}\mathrm{Si}$ and ${}^{30}\mathrm{Si}$ are determined by secondary ion mass spectrometry. Temperature dependence of the self-diffusion coefficients is accurately described over seven orders of magnitude with one diffusion enthalpy of 4.75 eV. This single enthalpy indicates that self-interstitials dominate self-diffusion. The high accuracy of our data enables us to estimate an upper bound for the vacancy-assisted diffusion enthalpy of 4.14 eV, which agrees with recent theoretical calculations.