Nature of the 0.111-eV acceptor level in indium-doped silicon

Strong evidence is presented that the X-level defect, which produces a 0.111-eV acceptor level in Si : In, is a substitional In–substitutional C (Ins-Cs) pair. The concentration of this defect follows a mass-action law with the In and C concentrations, the association constant being (1.4±0.3) ×10−19 cm−3 at 650 °C. Reversible changes in the X-level concentration between anneal temperatures of 650 and 850 °C are observed, and a pair binding energy of 0.7±0.1 eV is estimated. The electronic properties and temperature dependence of the concentration of this center are found to be those expected for a nearest-neighbor Ins-Cs pair.