Electronic structures ofGeSe2in crystalline, amorphous, and Ag-photodoped amorphous phases studied by photoemission and optical spectra

Both valence and conduction bands in crystalline, amorphous, and Ag-photodoped ${\mathrm{GeSe}}_2$ are studied by a combination of photoemission, core-exciton, and reflectance spectra by the use of synchrotron radiation. Two conduction-band levels are clarified through observation of Se and Ge 3d core-exciton spectra in both crystalline and amorphous phases. With use of the two conduction-band states and valence-band structures observed in the photoemission spectra, the fine structures in the energy second derivative of the dielectric-response spectra in the region of 1–20 eV are successfully interpreted. The fine structures in the amorphous spectra closely correspond to those in the crystalline spectra in energy. The binding energy of the lowest core excitons in amorphous ${\mathrm{GeSe}}_2$ is slightly smaller than that in the crystal. Core excitons are found to be smeared out in photodoped spectra.