Analysis of photoelectrical properties and current transient behaviour in TlBr

We had investigated photoelectrical and current transient properties of TlBr in the temperature region from -20 C up to +20 C, in which the effect of ionic conductivity changes significantly. The evaluated thermal activation energy value of conductivity of about 0.78 eV could stand for several mechanisms, e.g., electronic and ionic conductivity. From the spectral dependencies of photocurrent several defect-related maxima in the region between 1 and 2.5 eV were identified, being dependent on sample prehistory. Maximum at about 1.2 eV had appeared if the spectra were scanned from the high to the low quantum energies. Meanwhile the height of the maximum at about 2.1-2.2 eV used to decrease if the sample was kept biased for several hours. The transient photocurrent kinetics had demonstrated a complex behaviour that could be explained either by the combined trapping and/or recombination of light-generated carriers to the defect centres associated with potential inhomogeneities, followed by the growing ionic conduction or by a diffusion-related scattering variation in time. The evaluated thermal activation energy of the time constants of both processes was found to be 0.24 - 0.27 eV. The obtained results indicate that ionic conductivity can take place also at -20 C, though its influence is less because of the thermally activated character.