Anomalous photoconductivity in gamma In2Se3

Negative photoconductivity in indium selenide (γ-In2Se3) 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 (1.84eV) of the films, on varying indium concentration. Increase of indium concentration introduced defect levels at 1.46 and 1.32eV above the valance band. Photoluminescence study revealed the emission to a recombination center, which is situated at 290meV above valance band for all the samples. Levels at 1.46 and 1.32eV 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.