Oxygen assisted photoinduced changes in Ge39Ga2S59 amorphous thin film

Annealing of the Ge39Ga2S59 virgin amorphous thin film leads to the blue shift of the optical band gap owing to an increase of the film network order and to a decrease in the refractive index associated with both the film thickness expansion and a decrease in the mean molecular polarizability. Virgin film is only a little bleached by the illumination with the band gap or over band gap photons while the film annealed in the argon is practically insensitive to such illumination. Illumination by UV photons leads to significant changes in the surface topology of the virgin or annealed film. It is suggested that observed surface topology changes originate from the film oxidation, which is supported by: (i) Fourier transform infrared spectroscopy evidencing the presence of the broad absorption band in the region 750–900 cm−1 assigned to asymmetric stretching vibrations of the Ge–O–Ge bridge, (ii) the presence of the Raman feature at around 420 cm−1 assigned to symmetric stretching of bridging oxygen in O3Ge–O–GeO3 units and (iii) Atomic Force Microscopy indicating formation of some protrusions with entities reminiscent of isolated hexagonal particles which could be assigned to GeO2 microcrystalline particles.