Low-energy recoils in crystalline silicon: quantum simulations

Tight-binding molecular dynamics has been performed to study low-energy ~10-25 eV-recoil events in Si and to determine the threshold energies of atomic displacement for collision along the <111>, <-1-1-1>, and <100> directions. Since classical molecular dynamics has been widely used to simulate radiation-damage phenomena in Si, we found it of interest to compare tight-binding results with those obtained by classical calculations, using different forms of the empirical potentials. Results show that tight-binding simulations provide threshold energies that are, on average, lower than classical ones, and similar to those calculated with the Tersoff potential. The relevant difference between quantum and classical calculations is that the former systematically provide much larger relaxation energies of the defective configurations left at the end of the thermalization phase. This result may reveal a tendency to further evolution and, possibly, recombination of defects on a time scale relevant for microstructural evolution of implanted silicon.