Charge Transport and Observation of Persistent Photoconductivity in Tl 6 SeI 4 Single Crystals.

The chalcohalide compound Tl6 SeI4 is a promising wide-bandgap semiconductor for efficient hard radiation detection at room temperature due to its high density, average atomic number and mobility-lifetime product. However, the nature of its charge transport kinetics, especially the role of defects in recombination, has not been examined in detail. To determine the charge transport kinetics in Tl6 SeI4 single crystals, electrical conductivity and photoinduced current transient spectroscopy were measured over the temperature range 105-330 K. These measurements reveal the existence of multiple defect states with energy levels in the range 0.10-0.90 eV, within the bandgap of Tl6 SeI4 . Large persistent photoconductivity (PPC) is observed at low temperature that shows strong thermal quenching at 160 K. The quenching of PPC is described using a configuration coordinate model involving a deep level donor state, which is tentatively attributed to the presence of iodine vacancies or Si interstitial impurities.