Vacancy and vacancy-hydrogen complexes in silicon

The neutral vacancy (V) and the {V,${\mathrm{H}}_{\mathit{n}}$} (n=1,...,4) complexes in silicon are studied in various molecular clusters at the approximate ab initio and ab initio Hartree-Fock levels, with post-Hartree-Fock corrections in electron correlation. The quantities calculated are the equilibrium configurations and electronic structures, dissociation energies, diffusion paths, and activation energies. The dissociation energies are compared to those of other traps for H calculated at the same level of theory, such as substitutional C, interstitial Ti, or the {B,H} pair. The calculations predict that the {V,${\mathrm{H}}_1$} pair in Si should be mobile above room temperature. A part of the barrier for diffusion of {V,${\mathrm{H}}_1$} is lower than that of V, due to a mechanism analogous to the H-enhanced diffusion of interstitial O in Si. Another part of this barrier is higher than that for V. The consequences of this process include the possibility of enhanced diffusion of H in polycrystalline versus crystalline Si and leads us to propose a mechanism for the nucleation of platelets in the subsurface region of plasma-exposed Si.