Flowing damage in ion-implanted amorphous silicon

Using molecular-dynamics simulations, we have studied the creation and evolution of damage in crystalline and amorphous silicon following the implantation of energetic keV ions. A method is proposed to identify anomalous atoms based on a weighted combination of local, atomic-scale properties, which applies to both Si phases. For crystalline Si, the passage of the ions causes compact amorphous regions to form, while no evidence for melting is observed. The relaxation of the amorphouslike regions proceeds initially by the rapid recrystallization of smaller clusters and isolated atoms, followed by a long period of steplike changes in the number of defects due to spontaneous annealing of damage pockets at the crystalline-amorphous interface. In amorphous Si, the initial stage of damage annealing (which lasts a few picoseconds) resembles closely that observed in crystalline Si; on larger time scales, however, the damage is found to "percolate," or flow, through the system, inducing damage away from the collision cascade, thus causing an overall "derelaxation" of the material.