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

The electron mobility-lifetime product, μ
_e
τ
_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
_e
τ
_e
values 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
_e
τ
_e
. With an optimized filtering method (simple subtraction method), the measured μ
_e
τ
_e
values calculated using different methods at different biases were consistent. The μ
_e
τ
_e
values were also significantly higher than the results from conventional waveform filtering methods. Repeated measurements showed relative uncertainties of 20% for the μ
_e
τ
_e
values. Increased μ
_e
τ
_e
values were observed for CdZnTe detectors delivered by Redlen Technologies over the past several years. The μ
_e
τ
_e
values from the latest large volume pixelated CdZnTe detectors were about 0.05 cm
²
/V.