Formation of Frenkel pairs and diffusion of self-interstitial in Si under normal and hydrostatic pressure: Quantum-chemical 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 (I0) is the split configuration <110>. The tetrahedral configuration is not stable, an interstitial atom being shifted from T position in a new position T1 on a distance Δd=0.2 Å. 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: Ea (<110>→T1)=0.59 eV, Ea(T1→neighboring T1)=0.1 eV and Ea (T1→<110>)=0.23eV.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.