Vibrational properties of crystalline group-VI solids: Te, Se, S

Second-order Raman scattering is reported in the elemental crystalline group-VI systems of trigonal Te and Se, composed of chains, as well as monoclinic Se-ring and orthorhombic S-ring systems. As in elemental semiconductors and semimetals, the spectra are interpreted in terms of predominant overtone scattering that manifests features in the one-phonon density of states. For the chain structures the phonon spectra yield reasonable agreement with previous valence force models, although differences exist at high frequencies near the maximum phonon range. A comparison of the second-order spectra for the highest optic band indicates trends in the phonon spectra in the sequence $t$-Te, $t$-Se, $m$-Se, and $o$-S that are indicative of increasing molecular character associated with reduced interunit interactions. In contrast to chain structures, the ring systems are shown to indicate additional features in the phonon density of states. This is also observed in the corresponding noncrystalline phases.