Ab initio simulation of high pressure influence on He–H interaction in silicon

Abstract

To explain the high-pressure influence on He–H interaction in silicon we used the density functional theory and ab initio pseudopotentials. To simulate the pressure we reduced a silicon lattice constant by 1–5% that corresponds to the pressure of 1–5 GPa. Divacancies were used as models of voids in silicon. Calculations show that single He atoms accumulate in divacancies in the absence of external pressure. The 5 GPa pressure reduces the divacancy formation energy by about 1 eV in the absence of He. The presence of two He atoms in a divacancy reduces this value additionally by 0.3 eV. Thus, He stimulates formation of voids in silicon and fills them simultaneously. Leaving silicon interstitial sites for divacancies, H 2 molecules dissociate up and passivate silicon dangling bonds with the energy profit of 1.6 eV. The presence of two He atoms per divacancy reduces this profit by 0.1 eV. The 5 GPa pressure decreases this energy additionally by 0.3 eV and makes H in silicon less bonded and more mobile in accordance with experimental data.