Raman study of photostructural changes in amorphous GexSb0.4S0.6

Raman spectra of amorphous GexSb0.4-xS0.6 films and bulk samples have been measured for several values of x. The observed Raman bands are due to heteropolar M-S (M = Ge, Sb) bonds in the GeS4 tetrahedra and SbS3 pyramids, as well as homopolar (defective) M-M bonds whose population increases with increasing x.. Illumination of Ge-rich ternary films by band gap light induces photostructural changes, the most prominent of which being an increase of the relative population of M-M to M-S bonds. At larger intensities of illumination (by laser light), partial crystallization of Sb occurs in both films and bulk glasses and, again, this photostructural effect is larger in Ge-rich ternary samples. It is revealed that the SbS3 pyramidal population decreases after either of the above treatments, thus underlining the key role of the Sb-S bonds in the photostructural changes. Furthermore, the extent of these effects is discussed in terms of the defective bond population, the foe volume and dimensionality of the glassy network. (C) 1998 Elsevier Science B.V. All rights reserved.