Formation of Frenkel pairs and diffusion of self-interstitial in Si under normal and hydrostatic pressure: Quantumchemical simulation

Abstract

A theoretical modeling of the formation of Frenkel pairs and the diffusion of a self-interstitial atom in silicon crystals at normal and high (hydrostatic) pressures has been performed using quantum-chemical (NDDO-PM5), methods. It is shown that, in a silicon crystal, the most stable configuration of a self-interstitial atom in the neutral charge state ( I 0 ) is the split configuration 〈1 1 0〉. The tetrahedral configuration is not stable, an interstitial atom being shifted from T position in a new position T 1 on a distance Δ d =0.2 Å. The hexagonal configuration is not stable in NDDO approximation. The split 〈1 1 0〉 interstitial configuration remains the more stable configuration under hydrostatic pressure ( P <80 kbar). The activation barriers for diffusion of self-interstitial atoms in silicon crystals are determined to be as follows: E a (〈1 1 0〉→ T 1 )=0.59 eV, E a ( T 1 →neighboring T 1 )=0.1 eV and E a ( T 1 →〈1 1 0〉)=0.23 eV. The hydrostatic pressure ( P <80 kbar) increases the activation barrier for diffusion of self-interstitial atoms in silicon crystals. The energies of the formation of a separate Frenkel pair, a self-interstitial atom, and a vacancy are determined. It is demonstrated that the hydrostatic pressure decreases the energy of the formation of Frenkel pairs.