Raman study of photoinduced crystallization of SnS2 in As2S3:Sn glasses

Abstract

Raman spectra of synthesised As2S3:Sn samples with up to 2.7 at% Sn recorded at a moderate excitation power density (Pexc=4 kW/cm2) show their amorphous character. Raman measurements performed at a higher Pexc (40 kW/cm2) result in the local heating of the sample surface by up to 150 K, as estimated from the shift of the frequency positions of the As2S3 Raman maxima. For samples with Sn content above 2 at% a pronounced narrow peak at 311 cm–1 emerges as an evidence for SnS2 crystallites formed on the sample surface under above-bandgap illumination during the measurement. The higher-Pexc (40 kW/cm2) illumination results in a formation of a pit on the sample surface due to the material transfer and in a rapid decrease of the glass viscosity, enhancing the diffusion of atoms and facilitating their aggregation in SnS2 crystallites. This effect of mostly nonthermal nature is responsible for the SnS2-related feature observed in the Raman spectra upon illumination at Pexc= 40 kW/cm2. For As2S3 doped with 3 at% Sn the SnS2-related feature near 314 cm–1 is observed in the Raman spectra even under excitation at much lower Pexc, down to 0.4 kW/cm2. As follows from X-ray diffraction data, no crystalline SnS2 phase is present in this sample before the measurement, it appears upon illumination even at the low Pexc values.