On the basis of first-principles total-energy calculations, it was shown that most vacancies were trapped by interstitial O in wafers having a typical O concentration of about 1018/cm3. Vacancies and interstitial O formed so-called A-centres having a binding energy of 1.7eV. As a result, the density of bound vacancies exceeded the equilibrium density of free vacancies by several orders of magnitude, and the effective vacancy diffusion coefficients were reduced in comparison to the diffusion coefficient of free vacancies. However, it was found that the trapping of vacancies could not alone account for the large discrepancies between previously reported diffusion coefficients for vacancies.

Interaction of Vacancies with Interstitial Oxygen in Silicon. R.A.Casali, H.Rücker, M.Methfessel: Applied Physics Letters, 2001, 78[7], 913-5