Atomic Structure of SiS2and SiSe2Glasses

The first study of the atomic structure of Si chalcogenide glasses is reported. The Raman spectra are remarkably simple and can be understood in terms of the vibrations of a bitetrahedral ${\mathrm{Si}}_2{\left(X_{\frac{1}{2}}\right)}_8$ ($X=\mathrm{S},\mathrm{S}\mathrm{e}$) unit. The present results represent the most compelling evidence for medium-range order and a molecular-cluster description of a compound amorphous semiconductor.