Electronic structures of GeSe2 in crystalline, amorphous, and Ag-photodoped amorphous phases studied by photoemission and optical spectra.

Abstract

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.