Photoelectrical properties of TlBr related to ionic transport and presence of defects

Photoelectrical and current transient properties of TlBr were investigated in the temperature region from −20 up to +20 °C, in which effect of the ionic conductivity changes significantly. Non-monotonous conductivity change with temperature was identified, demonstrating mobility-related maximum superimposed on a band-to-band generation conductivity growth. This maximum could be caused by the recharge of the scattering centre at about 1.65 eV. Presence of such centre was confirmed by the photocurrent spectra. From spectral dependencies defect-related transitions at 0.55; 0.83, 1.1; 1.32 and 1.65 eV were identified, being dependent on sample prehistory, i.e., its excitation by light and/or voltage. The transient photocurrent kinetics have demonstrated a complex behaviour that could be explained by the combined influence of electron generation/recombination processes superimposed upon the effect of ionic conductivity. The results indicate that ionic conductivity can take place also at −20 °C, though its influence is less because of the thermally activated character.