Raman scattering studies of heavily doped microcrystalline porous silicon and porous silicon free-standing membranes
Résumé
The phonon confinement model is often used to analyze Raman scattering band shapes of porous silicon and hence to determine the size of crystallites embedded in the porous layer. We show in this paper, from back-scattering Raman spectra, the importance to avoid using resonant excitation which would select a particular size of nanocrystals. In nonresonant conditions, and working on free-standing porous silicon membranes, broader and more realistic size distributions are found. The disappearance of Fano effect evidences the loss of free carriers in the porous layer. Raman intensity angular variations in parallel and perpendicular polarization configurations are obtained and discussed. They show the presence of unexpected different constant offsets for these two configurations. By comparing with theoretical calculation we deduce that they sign the impact of the porous layer on the light propagation.