Carrier Lifetime and Mobility Characterization Using the DTU 3-D CZT Drift Strip Detector

• Published in: IEEE transactions on nuclear science Vol. 68; no. 9; pp. 2440 - 2446
• Main Authors: Owe, S. Howalt, Kuvvetli, I., Budtz-Jorgensen, C.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-09-2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 3-D CZT detectors; Carrier lifetime; carrier lifetime and mobility; Cathodes; Charge carrier lifetime; CZT drift strip detectors; Detectors; digitized pulse shape analysis; Drift; Energy resolution; Shape; Strip; Strips; Voltage measurement
• ISSN: 0018-9499; 1558-1578
• DOI: 10.1109/TNS.2021.3068001

At DTU Space, a 3-D CdZnTe (CZT) drift strip detector prototype of size 20 mm <inline-formula> <tex-math notation="LaTeX">\times4.7 </tex-math></inline-formula> mm <inline-formula> <tex-math notation="LaTeX">\times20 </tex-math></inline-formula> mm has been developed. It has demonstrated excellent submillimeter position resolution (<0.5mm) and energy resolution (<1.6%) at 661.6 keV using pulse shape signal processing. Signal formation on each of the 26 electrode readouts uses bipolar charge-sensitive preamplifiers. The output is sampled using high-speed digitizers, providing us with the full pulse shapes generated by each interaction in the detector. In order to optimize and understand the detector performance, a model of the 3-D CZT drift strip detector has been developed using COMSOL Multiphysics and Python. It simulates the 26 pulse shapes generated by an interaction and provides an output similar to that of the real detector setup. In order to create a trustworthy model, the material properties of the detector must be well understood. The generated pulse shapes are greatly affected by the electron mobility (<inline-formula> <tex-math notation="LaTeX">\boldsymbol \mu _{e} </tex-math></inline-formula>) and lifetime (<inline-formula> <tex-math notation="LaTeX">\boldsymbol \tau _{e} </tex-math></inline-formula>) of the detector material. Therefore, 3-D maps of <inline-formula> <tex-math notation="LaTeX">\boldsymbol \mu _{e} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">\boldsymbol \tau _{e} </tex-math></inline-formula> have been calculated as look-up tables for the model, utilizing the high-resolution 3-D interaction position and energy information provided by the 3-D CZT drift strip detector. In conclusion, the model performance is compared to real event data. We show that the model performance is greatly improved using the newly calculated 3-D maps compared to the uniform material properties provided by the crystal manufacturer.