ANISOTROPIC AND POLARIZATION EFFECTS IN RAMAN-SCATTERING IN POROUS SILICON

The polarized Raman scattering from porous silicon in the region of the fundamental optical phonon is shown to reveal marked anisotropic behaviour: its strength, frequency shift and line shape are markedly affected by the particular choice of scattering geometry. These effects are discussed within the framework of the standard phonon confinement model, also taking into account the partial breakdown of the polarization selection rules and the dispersion of the longitudinal optical and transverse optical phonon branches. The observed effects can be at least qualitatively understood by invoking the anisotropy of the phonon dispersion branches, whose relative contribution to the Raman signal varies with the polarization geometry and (possibly) with the sample morphology.