Fast and Slow Vacancies in Silicon

Vacancies (and probably also self-interstitials) in silicon appear to exist in several forms (atomic configurations) some of them being fast diffusers and other - slow diffusers. The data on enhanced self-diffusivity under proton irradiation, on vacancy and oxide precipitate profiles installed by Rapid Thermal Annealing, and on the self-diffusivity under equilibrium conditions suggest that there are at least two kinds of vacancy: 1) V-w - a fast-diffusing localized vacancy manifested in electron irradiated samples (Watkins vacancy), 2) V-s - a slow-diffusing extended vacancy manifested under hot proton irradiation. In RTA experiments, these two species behave as one equilibrated subsystem of a moderate effective diffusivity intermediate between those of V-w and V-s. There is also strong evidence in favor of a third kind of vacancy: V-f - a fast extended species, which controls the grown-in voids in silicon crystals.