Photoinduced and thermally induced bleaching of amorphous Ge─S films

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Abstract
The photoinduced changes of the optical properties of Ge27S73 thin films have been examined using visible and infrared spectroscopy. It was found that illumination of the virgin thin film in vacuum is accompanied by a blue shift of the optical gap and by an increase of the Ge─S bond density. If the film is illuminated in air, the blue shift of the gap is observed too, but the density of Ge─S bonds decreases and new extrinsic absorption bands around 820 and 695 cm−1 appear in the spectrum, indicating most probably the presence of Ge─O bonds. It is supposed that in the former case the photoinduced changes are most probably intrinsic (decreases of the randomness of the film structure), while in the second case the photoinduced bleaching is accompanied by photoinduced oxidation of the film.