Surface plasmon-polariton study of photoinduced diffusion in light-sensitive Ag–As2S3 thin-film structure

Abstract

This study explores photostimulated silver diffusion in an "Ag grating–As₂S₃ layer" structure using the surface plasmon-polariton (SPP) resonance method. The process was examined under illumination with light of various wavelengths (405, 532, and 632.8 nm). A silver diffraction grating with a 515 nm period and 20 nm relief depth, optimal for SPP excitation, served as the substrate. The kinetics of structural changes were monitored via the shape and angular shift of the SPP resonance in the specular reflection of p-polarized low-intensity He-Ne laser radiation. Differences in the optical properties of photodoped As₂S₃ layers exposed to light from spectral regions corresponding to interband transitions, as well as to transitions involving localized states within the As₂S₃ band gap, were revealed. These differences are shown to be associated with the specific mechanisms of photodoping under different exposure conditions. Irradiation with short-wavelength light (405 nm) results in intense generation of electron-hole pairs, formation of Ag–S bonds, and Ag₂S clusters, significantly increasing both the refractive index and the extinction coefficient of the chalcogenide layer. This leads to a substantial change in the angular position of the SPP resonance, with a relatively small change in its depth. In contrast, exposure to longer-wavelength radiation leads to photodoping primarily driven by internal photoemission of electrons, resulting in increased interface roughness and a significant decrease in plasmon resonance depth with only a small shift in its position.