Department of Physics, Faculty of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560, Japan
Abstract:
The characteristic A1 peak at 199 cm−1 in the Raman spectrum of amorphous GeSe2 were compared with the peaks at 211 and 216 cm−1 in the spectrum of crystalline GeSe2. It was proved that the crystalline 216 cm−1 peak is an intrinsic mode which is enhanced by the bulk exciton transition. From a model calculation using a valence force field and bond polarizability, the 211 cm−1 peak was assigned to in-phase breathing vibrations extended along the GeSe4 tetrahedral chain structure, while the 216 cm−1 peak was attributed to in-phase breathing vibrations quasi-localized at the GeSe4 edge-sharing tetrahedra. The phonon density of states in the crystal has a doublet peak similar to the amorphous Raman spectrum. A correspondence between the amorphous and the crystalline Raman spectra was proposed.