Self-interstitial trapping by carbon complexes in crystalline silicon

Abstract

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 ${C}_{I}{C}_{S}$ dicarbon complex, or with extra silicon and carbon interstitials. In particular, we identify and characterize two structures, namely, ${C}_{I}I$ and ${C}_{I}{C}_{I}.$ They are found energetically stable so that they could play a crucial role in the process of carbon aggregation. According to our calculations ${C}_{I}{C}_{I}$ may be formed by the interaction of one I with a ${C}_{I}{C}_{S},$ proving that the latter is not a deactivated trap for interstitials. Our results further suggest that ${C}_{I}I$ and ${C}_{I}{C}_{I}$ are seeds for further carbon aggregation.