Negative photoconductivity in indium selenide ͑␥-In 2 Se 3 ͒ thin films was observed at room temperature and was attributed to trapping of electrons and destruction of minority carriers during illumination through recombination. Photoconductivity of the films exhibited a strong dependence on the concentration of indium in the films. Photoconductivity decreased gradually and became negative as indium concentration increased. But there was no considerable variation in the optical band gap ͑1.84 eV͒ of the films, on varying indium concentration. Increase of indium concentration introduced defect levels at 1.46 and 1.32 eV above the valance band. Photoluminescence study revealed the emission to a recombination center, which is situated at 290 meV above valance band for all the samples. Levels at 1.46 and 1.32 eV prevented photogenerated carriers from reaching conduction band, during illumination. Thus the capture of conduction band electrons and destruction of minority carries via recombination, resulted in negative photoconductivity.

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Enhanced radiation tolerance in nitride multilayered nanofilms with small period-thicknesses Appl. Phys. Lett. 101, 153117 (2012) Strain controlled systematic variation of metal-insulator transition in epitaxial NdNiO3 thin films J. Appl. Phys. 112, 073718 (2012) Kinetics of color center formation in silica irradiated with swift heavy ions: Thresholding and formation efficiency Appl. Phys. Lett. 101, 154103 (2012) Fabricating high-density magnetic storage elements by low-dose ion beam irradiation Appl. Phys. Lett. 101, 112406 (2012) Determination of ion track radii in amorphous matrices via formation of nano-clusters by ion-beam irradiation ␥-In 2 Se 3 thin films prepared at different annealing temperatures ranging from 100 to 400°C were irradiated using 90 MeV Si ions with a fluence of 2 ϫ 10 13 ions/ cm 2 . X-ray diffraction analysis proved that there is no considerable variation in structural properties of the films due to the swift heavy ion irradiation. However, photosensitivity and sheet resistance of the samples increased due to irradiation. It was observed that the sample, which had negative photoconductivity, exhibited positive photoconductivity, after irradiation. The negative photoconductivity was due to the combined effect of trapping of photoexcited electrons, at traps 1.42 and 1.26 eV, above the valence band along with destruction of the minority carriers, created during illumination, through recombination. Photoluminescence study revealed that the emission was due to the transition to a recombination center, which was 180 meV above the valence band. Optical absorption study proved that the defects present at 1.42 and 1.26 eV were annealed out by the ion beam irradiation. This allowed photoexcited carriers to reach conduction band, which resulted in positive photoconductivity. Optical absorption study also revealed that the band gap of the material could be increased by ion beam irradiation. The sample prepared at 400°C had a band gap of 2 eV and this increased to 2.8 eV, after irradiation. The increase in optical band gap was attributed to the annihilation of localized defect bands, near the conduction and valence band edges, on irradiation. Thus, by ion beam irradiation, one could enhance photosensitivity as well as the optical band gap of ␥-In 2 Se 3 , making the material suitable for applications such as window layer in solar cells.

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