A molecular dynamics study of defect production due to low-energy collisions

Molecular dynamics (MD) simulations of collision cascades were studied in order to understand the effect of energy, temperature and direction of the primary knock-on atom (PKA) on the defect production in single crystal silicon for low-energy collision events. MD simulations were performed with ion energies ranging from 100 eV to 1 keV where the PKA was directed along the three major crystallographic directions at 0, 300 and 600 K. Collision cascades resulting from PKA energies above 100 eV appeared to undergo a solid- to liquid-like transformation at the height of the cascade event. Upon cooling, the liquid-like regions collapse resulting in the formation of numerous isolated defects and clusters of defects. We found that bulk and near-surface collision events followed the modified Kinchin-Pease model for defect production in silicon for the energies studied. Minimal temperature dependence was found for collision events that occurred in the bulk of the silicon crystal within the first 10 ps of the simulation.