Far-infrared absorption and Raman scattering studies in MeV C⁺- and C₂⁺-implanted InSb(111) crystals

Single crystal substrates of InSb(111) were implanted with C⁺ and C₂⁺ ions at implantation energies of 1.00 and 2.00 MeV, respectively, and a constant fluence of 5×10¹⁴ C atoms/cm² at room temperature. Raman scattering and FIR reflection measurements have been carried out on the implanted specimens as well as on a high-quality as-grown InSb crystal. Optical reflection spectra are presented for the implanted samples. These spectra, and their deviation from the reflection spectrum of crystalline InSb, are discussed in terms of the dielectric response model based on dielectric properties of the implanted region. The results indicate an increase of the carrier density as well as dielectric constant in the implanted specimens and, a decrease in the strength of the associated phonon mode. The damping constant changes by almost one order of magnitude. It is also found from both Raman and FIR data that in C₂⁺-implanted InSb samples the TO mode profile is broadened as compared to the samples implanted with C⁺ at the same energy/atom and at a constant fluence. A tentative explanation for these results is presented.