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

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 < 110 >. The tetrahedral configuration is not stable, an interstitial atom being shifted from T position in a new position T-1 on a distance Delta d = 0.2 angstrom. The hexagonal configuration is not stable in NDDO approximation. The split < 110 > 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 (< 110 > -> T-1) = 0.59 eV, E-a (T-1 -> neighboring T-1) = 0.1 eV and E-a (T-1 -> < 110 >) = 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. (C) 2009 Elsevier B.V. All rights reserved.