Interstitial carbon and the carbon-carbon pair in silicon: Semiempirical electronic-structure calculations

We report the results of semiempirical electronic-structure calculations for interstitial carbon and the carbon-carbon pair defects in silicon. We use the modified intermediate neglect of differential overlap version 3 (MINDO/3), the parametric method version 3, and modified neglect of diatomic overlap semiempirical methods in a finite-cluster framework to determine total energies with respect to atomic displacements, and predict defect stable and metastable geometries and vibrational frequencies. The MINDO/3 method correctly predicts the observed 〈100〉 split-interstitial geometry of the interstitial carbon and the bistability of the carbon-carbon pair. Other computational results suggest the possibility of additional metastable geometries and perhaps precursor geometries for both defect systems.