TOPICAL REVIEW: Structural and vibrational properties of carbon impurities in crystalline silicon
Si1-xCx alloys have been studied using self-consistent-charge density-functional-based tight-binding calculations. The origin of experimentally observed carbon-induced vibrational peaks near 475, 607 and 810 cm-1 are analysed, based on the theoretical calculations. The stability, vibrational frequencies, lattice relaxations, and energy gap variances of substitutional, interstitial single-carbon and dicarbon complexes in crystalline silicon are calculated. All the impurities induce severe lattice relaxations of adjacent Si atoms. The peak near 475 cm-1 originates from the lattice relaxations of Si atoms up to second-nearest neighbours from carbon impurities in all cases. The peak near 605 cm-1 originates mainly from the midbond interstitial carbon (which is at odds with general belief) whereas the high-energy peaks near 810 cm-1 result from the formation of the carbon complexes.