Development of Time-of-flight Measurement System for Carrier Transport Characterization of TlBr Semiconductor Detectors

Because thallium bromide (TlBr) semiconductor detectors with a wide bandgap show high detection efficiency and energy resolution, room-temperature gamma-ray spectrometers based on such detectors have been developed. In this study, we developed a system for evaluating the carrier transport properties in a TlBr detector, such as the mobility and the mobility–lifetime product (μτ product), in which the time-of-flight method is applied to charge carriers generated by a pulsed laser. In the developed system, the recombination effect and internal electric field distortion were experimentally confirmed to be negligible under the experimental conditions in this study. We determined the electron mobility and μτ product in the TlBr detector to be 25.3 cm²/Vs and 1.3 × 10⁻³ cm²/V, respectively. Because the laser spot diameter is less than 0.5 mm, the constructed measurement system allows the evaluation of the mobility and μτ product at a point on the crystal. It is also possible to evaluate the 2D distribution of the mobility and μτ product by scanning the laser irradiation position.