Simulations were made of the collision of 5keV Si atoms with a Si substrate. At this energy, the simulation provided an atomistic description of the evolution of the displacement cascade. The structure of the amorphous material was compared with that of rapidly quenched liquid Si. It was found that amorphous material remained when the cascades had cooled to room temperature. The average number of atoms in the amorphous regions was of the order of 800; in agreement with the 10eV/atom amorphization energy which had been reported for ion implantation in various systems. The structure of the amorphous regions was similar to that of bulk material which had been quenched from the melting point to 0K in 5ps. This was consistent with the fact that the cascade regions had a structure which was similar to that of liquid Si during the 2ps when the kinetic energy in the region was close to that of liquid Si. Tensile stresses arose from the collisions, and the density of the Si substrate increased. Finally, the 5keV primary knock-on atoms produced few, if any, isolated Frenkel pairs. However, the amorphous regions contained several hundred displaced atoms. These regions often contained fewer or more atoms when compared with the perfect crystal. Simulations of annealing for several ps at high temperatures could cause these regions to collapse into clusters of interstitials or vacancies. It was suggested that these defect clusters were mainly responsible for the enhanced diffusion of dopant atoms that was commonly observed in low-energy ion-implanted Si.

T.Diaz de la Rubia, G.H.Gilmer: Physical Review Letters, 1995, 74[13], 2507-10