X-ray response of CdZnTe detectors grown by the vertical Bridgman technique: Energy, temperature and high flux effects

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• 作者：L. Abbene^a ; ^{leonardo.abbene@unipa.it" class="auth_mail" title="E-mail the corresponding author} ; G. Gerardi^a ; A.A. Turturici^a ; G. Raso^a ; G. Benassi^b ; M. Bettelli^c ; N. Zambelli^b ; A. Zappettini^c ; F. Principato^a
• 关键词：CdZnTe detectors ; Boron oxide encapsulated vertical Bridgman ; X-ray and gamma ray detectors ; High flux ; Digital pulse shape analysis ; Energy-resolved photon counting detectors
• 刊名：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• 出版年：2016
• 出版时间：1 November 2016
• 年：2016
• 卷：835
• 期：Complete
• 页码：1-12
• 全文大小：3772 K

文摘

Nowadays, CdZnTe (CZT) is one of the key materials for the development of room temperature X-ray and gamma ray detectors and great efforts have been made on both the device and the crystal growth technologies. In this work, we present the results of spectroscopic investigations on new boron oxide encapsulated vertical Bridgman (B-VB) grown CZT detectors, recently developed at IMEM-CNR Parma, Italy. Several detectors, with the same electrode layout (gold electroless contacts) and different thicknesses (1 and 2.5 mm), were realized: the cathode is a planar electrode covering the detector surface (4.1×4.1 mm²), while the anode is a central electrode (2×2 mm²) surrounded by a guard-ring electrode. The detectors are characterized by electron mobility-lifetime product (µ_eτ_e) values ranging between 0.6 and 1·10⁻³ cm²/V and by low leakage currents at room temperature and at high bias voltages (38 nA/cm² at 10000 V/cm). The spectroscopic response of the detectors to monochromatic X-ray and gamma ray sources (¹⁰⁹Cd, ²⁴¹Am and ⁵⁷Co), at different temperatures and fluxes (up to 1 Mcps), was measured taking into account the mitigation of the effects of incomplete charge collection, pile-up and high flux radiation induced polarization phenomena. A custom-designed digital readout electronics, developed at DiFC of University of Palermo (Italy), able to perform a fine pulse shape and height analysis even at high fluxes, was used. At low rates (200 cps) and at room temperature (T=25 °C), the detectors exhibit an energy resolution FWHM around 4% at 59.5 keV, for comparison an energy resolution of 3% was measured with Al/CdTe/Pt detectors by using the same electronics (A250F/NF charge sensitive preamplifier, Amptek, USA; nominal ENC of 100 electrons RMS). At high rates (750 kcps), energy resolution values of 7% and 9% were measured, with throughputs of 2% and 60% respectively. No radiation polarization phenomena were observed at room temperature up to 1 Mcps (²⁴¹Am source, 60 keV), while a detector collapse characterizes the samples at T<10 °C.

Comparison with two traveling heater method (THM) grown CZT detectors (REDLEN, Canada), fabricated with the same electrode layout, is also presented.

These activities are in the framework of an Italian research project on the development of energy-resolved photon counting (ERPC) systems for high flux energy-resolved X-ray imaging.