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

At DTU Space, a 3-D CdZnTe (CZT) drift strip detector prototype of size 20 mm ×4.7 mm ×20 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 ( μe ) and lifetime ( τe ) of the detector material.

Therefore, 3-D maps of μe and τe 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.