Anomalous behaviour in dark conductivity and photoconductivity in a-Se85Te15 − xPbx thin films at low temperatures

Temperature dependence of dark conductivity and photoconductivity has been studied in amorphous thin films of Se85Te15 − xPbx (2 < x < 6) at low temperatures (219–300 K). We have observed that, at quite low temperatures, a maximum is found at a particular temperature in dark conductivity and photoconductivity measurements as a function of temperature. The position of this maximum shifts to higher temperatures at higher intensities. This behaviour is called anomalous as it is not commonly observed in chalcogenide glasses at low temperatures.Deep localized states, which behave like trapping centers, may play an important role in the conduction processes at low temperatures. The anomalous behaviour of dark conductivity is explained by considering a statistical shift of Fermi level with the change in temperature. The maxima in photoconductivity at low temperatures could be explained by assuming the sensitising centers in the mobility gap due to defect states.