Photo-induced changes of the short wavelength absorption edge in some Ge–As–S amorphous thin films

Abstract Amorphous films Ge27As13S60 (FII) and Ge14As27S59 (FIII) were prepared by thermal evaporation. Thermal and photo-induced bleaching were observed in the virgin films. Reversible photo-darkening was studied induced by various light sources (white light, monochromatic light with wavelengths 417 nm, 442 nm and 493 nm, respectively) in thermally well relaxed films. The role of actual conditions of illumination on the magnitude of photo-darkening (the incident photon flux and the penetration depth of absorbed photons) is examined. Considerable photo-darkening (dEg) observed in the studied films (dEg ≈ − 200 meV for Ge14As27S59 film) is tentatively attributed to possible disorder associated with nano-scale phase separation. Actually it is attributed to the photo-enhanced interaction between excited lone-pair orbitals of atoms on the cluster surfaces and/or to covalent bonds reconstruction/interaction of the cluster surfaces where existence of stressed bonds, which are supposed to be more susceptible to photo-induced excitation, breaking and reconstruction, is expected.