Atomic-scale simulations of cascade overlap and damage evolution in silicon carbide

In a previous computer-simulation experiment, the accumulation of damage in silicon carbide (SiC) from the overlap of 10 keV Si displacement cascades at 200 K was investigated, and the damage states produced following each cascade were archived for further analysis. In the current study, interstitial clustering, system energy, and volume changes are investigated as the damage states evolve due to cascade overlap. An amorphous state is achieved at a damage energy density of 27.5 eV/atom (0.28 displacements per atom). At low-dose levels, most defects are produced as isolated Frenkel pairs, with a small number of defect clusters involving only four to six atoms; however, after the overlap of five cascades (0.0125 displacements per atom), the size and number of interstitial clusters increases with increasing dose. The average energy per atom increases linearly with increasing short-range (or chemical) disorder. The volume change exhibits two regimes of linear dependence on system energy and increases more rapidly with dose than either the energy or the disorder, which indicates a significant contribution to swelling of isolated interstitials and antisite defects. The saturation volume change for the cascade-amorphized state in these simulations is 8.2%, which is in reasonable agreement with the experimental value of 10.8% in neutron-irradiated SiC.