Waveform Measurement of Mobility-Lifetime Products of CZT Detector Samples

This paper presents a waveform measurement of the induced signals from the bias-induced drift of the charge carriers — electrons and holes created by charge particles and high-energy photon interactions — within single-pixel CZT detector samples. The detectors were made from the material grown using the Accelerated Crucible Rotation Technique. CZT is well-recognized as a promising semiconductor material for gamma detection in SPECT and PET imaging due to the advantages of high energy resolution and high stopping power. To fully use these advantages, detectors made from spectroscopic-grade CZT material and understanding its trapping properties are necessary. The trapping property of a material is usually described by mobility-lifetime <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \tau$</tex> products of charge carriers. In this work, we used waveform readout to measure the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \tau$</tex> products of electrons and holes of various samples and detect depth-dependent photon signals, which can be later used in the estimation of depth-of-interaction (DOI) and corrections of the energy spectrum. We described the waveform signal capture with a mathematical model and estimated <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu_{\mathrm{e}} \tau_{\mathrm{e}}=1.19 * 10^{-3} ~\text{cm}^{2} / \mathrm{V}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu_{\mathrm{h}} \tau_{\mathrm{h}}=4.18 * 10^{-5} ~\text{cm}^{2} / \mathrm{V}$</tex> for a selected sample. This work presents an alternative method for assessing the quality of CZT in high-energy photon detection in medical imaging systems.