Photoemission studies of crystalline and amorphousSb2Se3

The photoemission energy distribution curves (EDC's) of crystalline and amorphous ${\mathrm{Sb}}_2$ ${\mathrm{Se}}_3$ were measured in the photon energy range $h\nu =7\mathrm{}$ to 35 eV using polarized radiation from a synchrotron storage ring. The polarization dependence of the EDC's is much stronger than that of the reflectance spectra. The EDC's show several regions of high density of states in both the valence and conduction bands, with the structure strongly smeared-out in amorphous ${\mathrm{Sb}}_2$ ${\mathrm{Se}}_3$. The region of the upper 2 eV of the valence band with six electrons per ${\mathrm{Sb}}_2$ ${\mathrm{Se}}_3$ molecule attributed primarily to the selenium lone $p$ pairs, is clearly separated from the remaining part of the EDC's in crystalline ${\mathrm{Sb}}_2$ ${\mathrm{Se}}_3$. The optical transitions in crystalline ${\mathrm{Sb}}_2$ ${\mathrm{Se}}_3$ occur with matrix elements strongly dependent on the orientation of the electrical vector of the polarized radiation as a result of crystal-field effects. Model densities of states are constructed for both crystalline and amorphous ${\mathrm{Sb}}_2$ ${\mathrm{Se}}_3$.