Photoinduced Change of Thermophysical Properties of Chalcogenide As2S3Thin Films

The reversible photoinduced change exhibited by amorphous chalcogenide glasses has been extensively studied recently, partly as an iInteresting subject for fundamental research in the field of disordered solids and partly due to potential applications in optoelectronics such as photoresists, optical memories, optoelectronic circuits, etc. The illumination of many amorphous chalcogenides changes their iInternal and/or surface structure while preserving their amorphous state. In this study, amorphous arsenic trisulfide (As2S3) thin film samples whose thickness is 5 m were prepared on silicon wafers by thermal evaporation, and their thermal diffusivity and thermal conductivity were measured by photoacoustic spectroscopy and a 3ω method, respectively. These measurements were repeated after illumination by an Ar+ laser beam whose photon energy Eg is consistent with the energy band gap of As2S3. The results show that the thermal diffusivity and thermal conductivity increase by about 50% and 14–15%, respectively, by the photoinduced darkening, and this can be explained by the rearrangement of atoms and thermal expansion of the film.