Mechanism of photo induced mass transfer in amorphous chalcogenide films

Surface relief gratings produced on a surface of amorphous chalcogenide films As₂₀Se₈₀ are flatten at room temperature under illumination by a near-bandgap polarized light (λ = 650 nm). The rates of the profiles flattening are dependent on the light intensity, polarization direction, and grating period. Two possible flattening mechanisms are selected: viscous flow and volume diffusion, and the flattening rates are calculated for both of them. From the comparison of the theory with the experiments, it is concluded that the process is controlled by anisotropic volume diffusion. The effective photo-induced diffusion coefficients, D_xx, along E-vector of the light polarization, obtained from the flattening kinetics are proportional to the light intensity (D_xx = β_xI) with β_x = 2.5 × 10^{- 18} m⁴/J. The diffusion coefficients D_yy along perpendicular direction are four times smaller, independently of the light intensity.