Carbon-tin defects in silicon

Infrared absorption experiments and ab initio computer simulations are used to study tin-carbon centers in silicon. Electron irradiation of C and Sn doped Si leads to prominent absorption lines at 873.5 and 1025 cm^-1. These are assigned to a carbon interstitial trapped by a substitutional Sn atom. The calculated modes are in good agreement with those observed. The calculations also suggest that a close-by pair of substitutional C and Sn will be a stable but electrically inert defect. This defect may account for the experimentally observed drop in the concentration of the Cₛ-Cᵢ defect after a room temperature annealing. Finally, we suggest Sn-C codoping of Si for manufacturing of radiation hard silicon.