Measurement of Electron Mobility-Lifetime Product in 3-D Position-Sensitive CdZnTe Detectors Using the VAD_UMv2.2 Digital Readout System

摘要

The electron mobility-lifetime product, μ_eτ_e, was calculated for seven large volume (2 × 2 × 1.5 cm^{3), 3-D position-sensitive CdZnTe detectors using the two-bias and depth-fitting methods. The anode and cathode signals were digitally sampled from preamplifiers and read out using the VAD_UM v2.2 electronic readout system. With conventional digital filters, the measured μ_eτ_evalues by depth-fitting were about 30% higher than the two-bias method. By analyzing the averaged waveforms, the effects of electron drift and detrapping were found to cause a significant underestimate of μ_eτ_e. With an optimized filtering method (simple subtraction method), the measured μ_eτ_evalues calculated using different methods at different biases were consistent. The μ_eτ_evalues were also significantly higher than the results from conventional waveform filtering methods. Repeated measurements showed relative uncertainties of 20% for the μ_eτ_evalues. Increased μ_eτ_evalues were observed for CdZnTe detectors delivered by Redlen Technologies over the past several years. The μ_eτ_evalues from the latest large volume pixelated CdZnTe detectors were about 0.05 cm2/V.}