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The focus of this paper is to evaluate thick, 20ϫ 20ϫ 10 and 10ϫ 10ϫ 10 mm 3 , cadmium zinc telluride ͑CZT͒, Cd 0.9 Zn 0.1 Te, crystals grown using the traveling heater method ͑THM͒. The phenomenal spectral performance and small size and low concentration of Te inclusions/precipitates of these crystals indicate that the THM is suitable for the mass production of CZT radiation detectors that can be used in a variety of applications. Our result also proves that with careful material selection using IR and high-quality fabrication processes, the theoretical energy resolution limit can be achieved.

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CdZnTe is a promising material for the current generation of free electron laser light sources and future laser-driven γ-ray sources which require detectors capable of high flux imaging at X-ray and γ-ray energies (> 10 keV). However, at high fluxes CdZnTe has been shown to polarise due to hole trapping, leading to poor performance. Novel Redlen CdZnTe material with improved hole transport properties has been designed for high flux applications. Small pixel CdZnTe detectors were fabricated by Redlen Technologies and flip-chip bonded to PIXIE ASICs. An XIA Digital Gamma Finder PIXIE-16 system was used to digitise each of the nine analogue signals with a timing resolution of 10 ns. Pulse shape analysis was used to extract the rise times and amplitude of signals. These were measured as a function of applied bias voltage and used to calculate the mobility (µ) and mobility-lifetime (µτ) of electrons and holes in the material for three identical detectors. The measured values of the transport properties of electrons in the high-flux-capable material was lower than previously reported for Redlen CdZnTe material (µ e τ e ∼ 1 × 10 −3 cm 2 V −1 and µ e ∼ 1000 cm 2 V −1 s −1 ) while the hole transport properties were found to have improved (µ h τ h ∼ 3 × 10 −4 cm 2 V −1 and µ h ∼ 100 cm 2 V −1 s −1 ).

Purpose Spectroscopic X‐ray detectors (SXDs) are under development for X‐ray imaging applications. Recent efforts to extend the detective quantum efficiency (DQE) to SXDs impose a barrier to experimentation and/or do not provide a task‐independent measure of detector performance. The purpose of this article is to define a task‐independent DQE for SXDs that can be measured using a modest extension of established DQE‐metrology methods. Methods We defined a task‐independent spectroscopic DQE and performed a simulation study to determine the relationship between the zero‐frequency DQE and the ideal‐observer signal‐to‐noise ratio (SNR) of low‐frequency soft‐tissue, bone, iodine, and gadolinium signals. In our simulations, we used calibrated models of the spatioenergetic response of cadmium telluride (CdTe) and cadmium–zinc–telluride (CdZnTe) SXDs. We also measured the zero‐frequency DQE of a CdTe detector with two energy bins and of a CdZnTe detector with up to six energy bins for an RQA9 spectrum and compared with model predictions. Results The spectroscopic DQE accounts for spectral distortions, energy‐bin‐dependent spatial resolution, interbin spatial noise correlations, and intrabin spatial noise correlations; it is mathematically equivalent to the squared SNR per unit fluence of the generalized least‐squares estimate of the height of an X‐ray impulse in a uniform noisy background. The zero‐frequency DQE has a strong linear relationship with the ideal‐observer SNR of low‐frequency soft‐tissue, bone, iodine, and gadolinium signals, and can be expressed in terms of the product of the quantum efficiency and a Swank noise factor that accounts for DQE degradation due to, for example, charge sharing (CS) and electronic noise. The spectroscopic Swank noise factor of the CdTe detector was measured to be 0.81 ± 0.04 and 0.83 ± 0.04 with and without anticoincidence logic for CS suppression, respectively. The spectroscopic Swank noise factor of the CdZnTe detector operated with four energy bins was measured to be 0.82 ± 0.02 which is within 5% of the theoretical value. Conclusions The spectroscopic DQE defined here is (1) task‐independent, (2) can be measured using a modest extension of existing DQE‐metrology methods, and (3) is predictive of the ideal‐observer SNR of soft‐tissue, bone, iodine, and gadolinium signals. For CT applications, the combination of CS and electronic noise in CdZnTe spectroscopic detectors will degrade the zero‐frequency DQE by 10 %–20 % depending on the electronic noise level and pixel size.

Purpose We present a new framework for theoretical analysis of the noise power spectrum (NPS) of photon‐counting x‐ray detectors, including simple photon‐counting detectors (SPCDs) and spectroscopic x‐ray detectors (SXDs), the latter of which use multiple energy thresholds to discriminate photon energies. Methods We show that the NPS of SPCDs and SXDs, including spatio‐energetic noise correlations, is determined by the joint probability density function (PDF) of deposited photon energies, which describes the probability of recording two photons of two different energies in two different elements following a single‐photon interaction. We present an analytic expression for this joint PDF and calculate the presampling and digital NPS of CdTe SPCDs and SXDs. We calibrate our charge sharing model using the energy response of a cadmium zinc telluride (CZT) spectroscopic x‐ray detector and compare theoretical results with Monte Carlo simulations. Results Our analysis shows that charge sharing increases pixel signal‐to‐noise ratio (SNR), but degrades the zero‐frequency signal‐to‐noise performance of SPCDs and SXDs. In all cases considered, this degradation was greater than 10%. Comparing the presampling NPS with the sampled NPS showed that degradation in zero‐frequency performance is due to zero‐frequency noise aliasing induced by charge sharing. Conclusions Noise performance, including spatial and energy correlations between elements and energy bins, are described by the joint PDF of deposited energies which provides a method of determining the photon‐counting NPS, including noise‐aliasing effects and spatio‐energetic effects in spectral imaging. Our approach enables separating noise due to x‐ray interactions from that associated with sampling, consistent with cascaded systems analysis of energy‐integrating systems. Our methods can be incorporated into task‐based assessment of image quality for the design and optimization of spectroscopic x‐ray detectors.

Over the last two decades, the II-VI semiconductors CdTe and CdZnTe (CZT) has emerged as the material of choice for room temperature detection of hard X-rays and soft γ-rays. The techniques of growing the crystals, the design of the detectors, and the electronics used for reading out the detectors have been considerably improved over the last few years. CdTe/CZT materials find now applications in astrophysics, medical imaging and security applications. The paper discusses recent progress in CZT detector technology and outlines possible new application opportunities.

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