Critical-point analysis of the two-phonon Raman spectrum of silicon

Abstract

Two-phonon Raman spectrum of silicon has been measured in back-scattering configuration at room temperature using Argon ion laser. It reveals many critical points and consists mainly of two-phonon overtone states. The agreement between the calculated density of states from neutron diffraction data and the present Raman spectrum is excellent except the region where combination spectrum appears. Polarization measurement shows that the structure centered at 300 cm −1 is not the one-phonon fine structure, predicted by Cowley and observed in part and identified as such by Wright and Mooradian, but the two-phonon overtone spectrum of acoustic phonons. Critical-point analysis has been done on the two-phonon overtone and combination spectra, and phonon frequencies of points of high symmetry in the Brillouin zone are determined and compared with other experimental results. In contrast to the Raman spectrum of diamond, no peak was observed near twice the frequency of zone-center optical phonon. This fact is explained by the difference of phonon dispersion relation between diamond and silicon.