Photobleaching in a g-Ge 0.27Sn 0.03Se 0.7 thin film

Abstract

Photobleaching was observed by optical transmission measurements performed using constant 655 nm (sub-band gap) illumination of a g-Ge 0.27Sn 0.03Se 0.7 thin (<2 μm) film sample deposited by thermal evaporation of bulk starting materials on silica. The threshold power density for destroying the film was 2.7 kW cm −2 for a film thickness of 1.75 μm. The effective thermal conductivity was calculated and the temperature increase in the illuminated spots was estimated. A little below the destruction threshold photobleaching may be attributed to band gap increase with thermal annealing. But photobleaching is also observed at low power densities inducing spot temperatures well below the glass transition. No noticeable crystallization of the bleached film region was observed either optically or by X-ray diffraction.