Energy band-gap inhomogenities and defect states affecting carrier transport at low temperatures in Thallium Bromide

Abstract We report analysis of carrier transport phenomena in Thallium Bromide single-crystals-based ionizing radiation detectors. It is demonstrated that these phenomena, despite the used mature material growth technology, are in general notably affected by still present material macro-inhomogeneities. The inhomogeneities, which are well discerned by optical microscopy and AFM, reveal themselves in carrier transport, causing the space-charge-limited currents, appearance of the built-in polarization voltages and long lasting (photo-) conductivity relaxations at low temperatures. They could be associated with the existing charge trapping states and potential inhomogeneities of the band gap edges, which create potential fluctuations of up to 240 meV. These fluctuations become thermally quenched by the thermally generated carriers above about 260 K.