Vacancies and {V,H_n} complexes in Si: Stable structures, relative stability, and diffusion properties

The equilibrium configurations of the neutral vacancy in Si and of the {V,H_n} complexes with n = 1,...,4 are calculated. The geometries and structures agree with earlier descriptions. The barrier for diffusion of the neutral vacancy is obtained at various levels of theory, from `approximate ab-initio' Hartree-Fock (HF) to large basis set ab-initio HF followed by post-HF corrections in electron correlation (MP2). We also investigate the diffusion mechanism and barrier for the {V,H}⁰ pair. Preliminary results show that this pair is likely to be mobile, while vacancies containing more than one H are not. Some consequences of the mobility of the {V,H}⁰ pair related to the observed enhanced diffusion of hydrogen in polycrystalline Si are discussed.