Experimental Evidence of the Vacancy-Mediated Silicon Self-Diffusion in Single-Crystalline Silicon

We have determined silicon self-diffusivity at temperatures 735--875 ^∘C based on the Raman shift of longitudinal optical phonon frequencies of diffusion annealed ²⁸Si/³⁰Si isotope superlattices. The activation enthalpy of 3.6 eV is obtained in such low temperature diffusion annealing. This value is significantly smaller than the previously reported 4.95 eV of the self-interstitial mechanism dominating the high temperature region T855 ^∘C and is in good agreement with the theoretical prediction for the vacancy-mediated diffusion. We present a model, containing both the self-interstitial and the vacancy terms, that quantitatively describes the experimentally obtained self-diffusivity between 735 and 1388 ^∘C, with the clear crossover of the two diffusion mechanisms occurring around 900 ^∘C.