Study on the Edge Effect in Transport Property Evaluation of Laser-induced Carriers in TlBr Semiconductors

TlBr has high detection efficiency and energy resolution and is also considered a semiconductor detector material that can be operated at room temperature.We have developed and improved a system to evaluate the mobility of charge carriers generated by a pulsed laser using the time-of-flight (TOF) technique.With this system, it is possible to evaluate the twodimensional distribution of charge transport properties by scanning the laser irradiation positions.In this study, we have considered the shape changes of the signal waveform depending on the laser irradiation positions through comparisons between experimental and simulation results.Since the signal shape change is especially severe near the edge of the electrode, this effect is referred to as the edge effect.For the detector having small electrodes compared with the crystal surface, the electric field near the electrode edges is severely disturbed.Consequently, the mobility of electrons generated near the edge of the electrode might be underestimated.To evaluate mobility more accurately, it is desirable to form electrodes over the entire crystal surface as much as possible to create a uniform electric field between the electrodes.