Fano-type interference in the Raman spectrum of photoexcited Si

Free carriers introduced by high cw laser power densities (2×10⁶ to 4×10⁷W/cm²) in silicon result in a Fano-type asymmetric Raman line shape. This line shape is attributed to the interaction between the photoexcited holes and the zone center optical phonon. Raman spectra of photoexcited Si are compared with p-doped Si spectra in a wide temperature range (5–750 K) for different laser wavelengths. The determination of the free carrier plasma concentration from the Raman spectrum is demonstrated. These measurements provide an additional source of information on recombination rates, ambipolar diffusion, and electron-phonon coupling parameters for dense electron-hole plasma (up to 4×10¹⁹cm^-3).