Weakly bound carbon-hydrogen complex in silicon

Local vibrational modes of a weakly bound carbon-hydrogen complex in silicon have been identified with infrared-absorption spectroscopy. After implantation of protons at ∼20 K and subsequent annealing at 180 K, two carbon modes at 596 and 661 ${\mathrm{cm}}^{\mathrm{-}1}$, and one hydrogen mode at 1885 ${\mathrm{cm}}^{\mathrm{-}1}$ are observed. The three modes originate from the same complex, which is identified as bond-centered hydrogen in the vicinity of a nearby substitutional carbon atom. Ab initio theory has been applied to calculate the structure and local modes of carbon-hydrogen complexes with hydrogen located at the first, second, and third nearest bond-center site to substitutional carbon. The results support our assignment.