Self-interstitial trapping by carbon complexes in crystalline silicon

By combining model-potential molecular-dynamics simulations and ab initio calculations we investigate the microscopic mechanism of silicon trapping by carbon substitutional defects (C-S). We find that, upon silicon trapping, carbon is converted into an interstitial mobile complex (C-I) by an efficient exothermic reaction. Interstitial carbon C-I may further interact either with another C-S, forming the well-known CICS dicarbon complex, or with extra silicon and carbon interstitials. In particular, we identify and characterize two structures, namely, CII and CICI. They are found energetically stable so that they could play a crucial role in the process of carbon aggregation. According to our calculations CICI may be formed by the interaction of one I with a CICS, proving that the latter is not a deactivated trap for interstitials. Our results further suggest that CII and CICI are seeds for further carbon aggregation.