Evidence of homopolar bonds in chemically stoichiometric Ge_xAs_ySe_1-x-y glasses

We prepared five samples of chemically stoichiometric Ge_xAs_ySe_1-x-y glasses in order to examine whether homopolar bonds exist in these glasses. It is generally accepted that the structure of these chemically stoichiometric glasses should be dominated by GeSe_4/2 tetrahedra and AsSe_3/2 pyramids with a negligible quantity of homopolar bonds. Analysis of Raman scattering and X-ray photoelectron spectra of the glasses indicates that, while glasses located at the center of the glass-forming region primarily contain heteropolar bonds, a considerable number of homopolar bonds exists in glasses with extremely high Ge or As concentrations. This demonstrates that the formation of homopolar bonds might be intrinsic to chemically stoichiometric chalcogenide glasses.