The (Ge2S3)x(As2S3)1-x chalcogenide glass thin films, with x = 0.1, 0.7 and 0.9 were prepared by flash thermal evaporation of glass powders. Their average coordination numbers were Z = 2.52, 2.68, 2.78 respectively. Samples were deposited on c-Si substrate with an Al interlayer. The Raman spectra were recorded with a DILOR Z-24 triple spectrometer and FT-Raman module of Perkin-Elmer GX spectrometer. The excitation were green line λ = 514.5 nm (E=2.41 eV) from Ar-ion laser, and near infrared line λ=1064 nm (E=1.17 eV) from Nd:YAG laser. Fig. 1 shows Raman spectra of (Ge2S3)x(As2S3)1-x samples with different coordination numbers excited with light of two different energies. Two major bands can be identified in those spectra, one between 200 and 280 cm-1 and the other between 300 and 450 cm-1. Band positions in Raman spectra, recorded from sample with threshold coordination number Z = 2.68 , are similar for both excitation energies. On the contrary, the spectra of samples with Z = 2.52 and Z = 2.78 exhibit a shift of peak positions in dependence to the excitation energy. That shift is discussed in terms of structural ordering at the threshold Z and its connection with the band-tail states.

Fizika,Kemija