Structures and stabilities of small carbon interstitial clusters in cubic silicon carbide

Knowledge of the configurations and stabilities of defect clusters in SiC is important for understanding radiation damage in this material, which is relevant to its nuclear and electronic applications. Such information is, however, often difficult to obtain experimentally. In this study, we perform Monte Carlo basin-hopping simulations with both empirical potential and density functional theory (DFT) calculations to search for the ground state (GS) configurations of small carbon interstitial clusters and carbon–antisite-based defects in cubic SiC (3C–SiC). Educated guesses of possible GS configurations have also been made. Our new approach can successfully identify many hitherto unknown GSs and energetically highly competitive metastable structures. For carbon penta- and hexa-interstitials, the GS structures predicted by DFT and empirical potential differ, and the plausible origin of this discrepancy is discussed from the chemical bonding point of view. Surprisingly, the GS structures of large carbon interstitial clusters in SiC are disjointed and composed of di- and tri-interstitial clusters as fundamental building blocks. Based on the present results, a possible mechanism for the carbon tri-interstitial defect to grow into the extended {1 1 1} planar interstitial defects observed in neutron-irradiated 3C–SiC is proposed. Furthermore, we show that C interstitial clusters can get trapped at a carbon antisite and form very stable complexes in SiC.