Quantification of ionic migration in TlBr gamma-ray detector via temperature-dependent conductivity measurements

Abstract

Thallium bromide (TlBr) is a promising room-temperature gamma-ray detector material owing to its high atomic number, wide bandgap, and relatively simpler crystal growth process than CdTe-based crystals. However, its practical application is hindered by ionic migration and polarization effects that degrade long-term stability under high bias voltages. In this work, we present a quantitative methodology to evaluate ionic transport in TlBr detectors through temperature-dependent conductivity measurements in the 193–323 K range. By separating electronic and ionic contributions under both current- and voltage-bias conditions, we extracted ionic conductivity values and determined the activation energy of ion migration. The activation energy varied with the vertical position of zone-refined TlBr ingots. These values were correlated with device performance, including photocurrent degradation under X-ray irradiation and peak channel shifts in gamma-ray spectra. The results reveal that ionic migration critically impacts charge collecting ability and spectral stability. This study proposed a standardized framework for quantifying ionic migration in TlBr detectors, offering valuable guidance for evaluating the operational stability in TlBr detectors. The activation energy of ion migration can serve as a robust metric for quantitatively comparing compound semiconductor detectors, whose ions migrate.