Inversion of the direction of photo-induced mass transport in As ₂₀Se₈₀ films: Experiment and theory

Diffusion mass transfer in thin chalcogenide films under illumination by a focused Gaussian beam have been studied both experimentally and theoretically. It is demonstrated that depending on the light intensity, waist of the beam, and the film thickness, one can obtain formation of either hillocks or dips in the illuminated regions. By comparison of the kinetics of hillock or dip formation on a surface of As₂₀Se₈₀ glass films with the results of our theoretical analysis, we have estimated the photo-induced diffusion coefficients, D, at various light intensities, I, and found D to be proportional to I (D I), with ≈ 1.5 10^-18 m⁴/J.