Since the late 2000s, the availability of high-quality cadmium zinc telluride (CdZnTe) has greatly increased. The excellent spectroscopic performance of this material has enabled the development of detectors with volumes exceeding 1 cm3 for use in the detection of nuclear materials. CdZnTe is also of great interest to the photon science community for applications in X-ray imaging cameras at synchrotron light sources and free electron lasers. Historically, spatial variations in the crystal properties and temporal instabilities under high-intensity irradiation has limited the use of CdZnTe detectors in these applications. Recently, Redlen Technologies have developed high-flux-capable CdZnTe material (HF-CdZnTe), which promises improved spatial and temporal stability. In this paper, the results of the characterization of 10 HF-CdZnTe detectors with dimensions of 20.35 mm × 20.45 mm × 2.00 mm are presented. Each sensor has 80 × 80 pixels on a 250-μm pitch and were flip-chip-bonded to the STFC HEXITEC ASIC. These devices show excellent spectroscopic performance at room temperature, with an average Full Width at Half Maximum (FWHM) of 0.83 keV measured at 59.54 keV. The effect of tellurium inclusions in these devices was found to be negligible; however, some detectors did show significant concentrations of scratches and dislocation walls. An investigation of the detector stability over 12 h of continuous operation showed negligible changes in performance.
Real-time Pockels imaging is performed on semi-insulating CdZnTe to measure the electric field profile in the material bulk. In steady-state room temperature conditions the measured electric field profile is uniform, consistent with a low space charge concentration. At temperatures Ͻ270 K a significant nonuniform electric field profile is observed, which we explain in terms of temperature-induced band bending at the metal-semiconductor interface, causing the formation of positive space charge in the bulk. Similar electric field distortion effects are observed when room temperature CdZnTe is irradiated by x-rays, causing a high rate of photoinduced charge injection.
The internal electric field distribution in cadmium zinc telluride (CdZnTe) X-ray andray detectors strongly affects their performance in terms of charge transport and charge collection properties. In CdZnTe detectors the electric field distribution is sensitively dependant on not only the nature of the metal contacts but also on the working conditions of the devices such as the temperature and the rate of external irradiation. Here we present direct measurements of the electric field profiles in CdZnTe detectors obtained using the Pockel electo-optic effect whilst under in-situ X-ray irradiation. These data are also compared with alpha particle induced current pulses obtained by the transient current technique (TCT), and we discuss the influence of both low temperature and X-ray irradiation on the electric field evolution. Results from these studies reveal strong distortion of the electric field consistent with the build-up of space charge at temperatures below 250K, even in the absence of external irradiation. Also, in the presence of X-ray irradiation levels a significant distortion in the electric field is observed even at room temperature which matches well the predicted theoretical model.
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