Ionic current and polarization effect in TlBr

Thallium bromide (TlBr) is an ionic semiconductor that has shown great capacity for accurate radiation detection. Its application to this end, however, has been hampered by degradation of performance overtime, in a process called polarization. This effect has been traditionally assigned to a build-up of ions at the electrodes, which would counteract an applied electrical bias field. Here, we estimate the ionic mobility in TIBr and its possible association with the polarization effect using parameter-free quantum simulations. Our results indicate that in samples with up to moderate levels of impurities, ions cannot traverse distances large enough to generate zones of accumulation and depletion in the crystal, suggesting different causes for the polarization effect.