Bistable interstitial-carbon–substitutional-carbon pair in silicon

A bistable interstitial-carbon--substitutional-carbon pair has been identified in electron-irradiated silicon by a combination of several spectroscopic experimental techniques. In the positive and negative charge states, the stable configuration of the defect involves a carbon-silicon ``molecule'' which occupies a single lattice site (each atom threefold coordinated) next to a substitutional-carbon atom (fourfold coordinated). In the neutral charge state, the defect rearranges its bonds so that both carbon atoms become substitutional (fourfold coordinated) with a twofold-coordinated silicon atom nestled between them. Detailed microscopic models and configurational-coordinate energy surfaces for each of the three charge states have been obtained.