Effect of Deep-Level Defects on the Performance of CdZnTe Photon Counting Detectors

The effect of deep-level defects is a key issue for the applications of CdZnTe high-flux photon counting devices of X-ray irradiations. However, the major trap energy levels and their quantitive relationship with the device’s performance are not yet clearly understood. In this study, a 16-pixel CdZnTe X-ray photon counting detector with a non-uniform counting performance is investigated. The deep-level defect characteristics of each pixel region are analyzed by the current–voltage curves (I–V), infrared (IR) optical microscope photography, photoluminescence (PL) and thermally stimulated current (TSC) measurements, which indicate that the difference in counting performance is caused by the non-uniformly distributed deep-level defects in the CdZnTe crystals. Based on these results, we conclude that the CdZnTe detectors with a good photon counting performance should have a larger Te cd 2 + and Cd vacancy-related defect concentration and a lower A-center and Tei concentration. We consider the deep hole trap Tei, with the activation energy of 0.638–0.642 eV, to be the key deep-level trap affecting the photon counting performance. In addition, a theoretical model of the native defect reaction is proposed to understand the underlying relationships of resistivity, deep-level defect characteristics and photon counting performance.

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Dual energy X-ray beam ptycho-fluorescence imaging

Journal of Synchrotron Radiation ◽

10.1107/s1600577521008675 ◽

2021 ◽

Vol 28 (6) ◽

Author(s):

Silvia Cipiccia ◽

Francesco Brun ◽

Vittorio Di Trapani ◽

Christoph Rau ◽

Darren J. Batey

Keyword(s):

Fresnel Zone ◽

Imaging Techniques ◽

Photon Counting ◽

Field Of View ◽

Step Size ◽

X Ray ◽

Single Beam ◽

Photon Counting Detector ◽

Nanoscale Imaging ◽

The Difference

X-ray ptychography and X-ray fluorescence are complementary nanoscale imaging techniques, providing structural and elemental information, respectively. Both methods acquire data by scanning a localized beam across the sample. X-ray ptychography processes the transmission signal of a coherent illumination interacting with the sample, to produce images with a resolution finer than the illumination spot and step size. By enlarging both the spot and the step size, the technique can cover extended regions efficiently. X-ray fluorescence records the emitted spectra as the sample is scanned through the localized beam and its spatial resolution is limited by the spot and step size. The requisites for fast ptychography and high-resolution fluorescence appear incompatible. Here, a novel scheme that mitigates the difference in requirements is proposed. The method makes use of two probes of different sizes at the sample, generated by using two different energies for the probes and chromatic focusing optics. The different probe sizes allow to reduce the number of acquisition steps for the joint fluorescence–ptychography scan compared with a standard single beam scan, while imaging the same field of view. The new method is demonstrated experimentally using two undulator harmonics, a Fresnel zone plate and an energy discriminating photon counting detector.

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Investigation on X-ray Photocurrent Response of CdZnTe Photon Counting Detectors

Sensors ◽

10.3390/s20020383 ◽

2020 ◽

Vol 20 (2) ◽

pp. 383 ◽

Cited By ~ 1

Author(s):

Yingrui Li ◽

Gangqiang Zha ◽

Yu Guo ◽

Shouzhi Xi ◽

Lingyan Xu ◽

...

Keyword(s):

Carrier Transport ◽

Photon Counting ◽

Photocurrent Response ◽

Applied Bias ◽

Critical Flux ◽

X Ray ◽

Photon Counting Detector ◽

Field Distortion ◽

Photon Counting Detectors ◽

Cdznte Detectors

Counting rate is an important factor for CdZnTe photon counting detectors as high-flux devices. Until recently, there has been a lack of knowledge on the relationship between X-ray photocurrent response and the photon counting performance of CdZnTe detectors. In this paper, the performance of linear array 1 × 16-pixel CdZnTe photon counting detectors operated under different applied biases is investigated. The relation between experimental critical flux and applied bias show an approximate quadratic dependence, which agrees well the theoretical prediction. The underlying relationship among X-ray photocurrents, carrier transport properties, and photon counting performance was obtained by analyzing X-ray current–voltage and time current curves. The typical X-ray photocurrent curve can be divided into three regions, which may be explained by the photoconductive gain mechanism and electric field distortion characteristics. To keep CdZnTe photon counting detectors working in a “non-polarized state”, the applied bias should be set on the left side of the “valley region” (high bias direction) in the X-ray I-V curves. This provides an effective measurement for determining the proper working bias of CdZnTe detectors and screening photon counting detector crystals.

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Compositional Modulation and its Optoelectric Properties of Zn(S,Se,Te) Crystals Grown by Hydrogen Radical-Enhanced CVD

MRS Proceedings ◽

10.1557/proc-417-253 ◽

1995 ◽

Vol 417 ◽

Author(s):

Hiroyuki Fujiwara ◽

Toshihiro Ii ◽

Isamu Shimizu

Keyword(s):

Deep Level ◽

Chemical Vapor ◽

X Ray Diffraction ◽

Small Shift ◽

X Ray ◽

Compositional Modulation ◽

Peak Energy ◽

Large Lattice ◽

The Difference ◽

Hydrogen Radical

AbstractHigh-quality (ZnS)n(ZnSe)12n and (ZnSe)n(ZnTe)11n (n=1∼4) crystals were grown at a low temperature of 200°C by hydrogen radical-enhanced chemical vapor deposition. From satellite peaks in x-ray diffraction spectra, these periodic structure crystals were confirmed to be grown coherently on substrates, in spite of large lattice mismatches between the grown layers and the substrates (͛=4∼7%). In photoluminescence (PL) spectra of these films, strong band-edge emissions were predominantly observed, resulting from a suppression of deep-level emissions. We found that the PL peak energy of (ZnSe)n(ZnTe)11n shifts systematically to lower energy by 200 meV with changes in the number of ZnSe layers (n), while relatively small shift of 13 meV was observed in (ZnS)n(ZnSe)12n. These discrepancy can be attributed to the difference of band-lineups or chemical natures of constituent atoms in these crystals.

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The significance of the spectral correction of photon counting detector response in material classification from spectral x-ray CT

Quantum Optics and Photon Counting 2021 ◽

10.1117/12.2589290 ◽

2021 ◽

Author(s):

Doniyor Jumanazarov ◽

Ja-Keoung Koo ◽

Henning F. Poulsen ◽

Ulrik L. Olsen ◽

Mihai Iovea

Keyword(s):

Photon Counting ◽

Detector Response ◽

X Ray ◽

Photon Counting Detector ◽

Material Classification ◽

Spectral Correction

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Evaluation and comparison of a CdTe based photon counting detector with an energy integrating detector for X-ray phase sensitive imaging of breast cancer

Journal of X-Ray Science and Technology ◽

10.3233/xst-211028 ◽

2021 ◽

pp. 1-13

Author(s):

Muhammad U. Ghani ◽

Farid H. Omoumi ◽

Xizeng Wu ◽

Laurie L. Fajardo ◽

Bin Zheng ◽

...

Keyword(s):

Breast Cancer ◽

Spatial Resolution ◽

Standard Dose ◽

Photon Counting ◽

High Energy ◽

Edge Enhancement ◽

X Ray ◽

Photon Counting Detector ◽

Phase Sensitive ◽

Observer Studies

PURPOSE: To compare imaging performance of a cadmium telluride (CdTe) based photon counting detector (PCD) with a CMOS based energy integrating detector (EID) for potential phase sensitive imaging of breast cancer. METHODS: A high energy inline phase sensitive imaging prototype consisting of a microfocus X-ray source with geometric magnification of 2 was employed. The pixel pitch of the PCD was 55μm, while 50μm for EID. The spatial resolution was quantitatively and qualitatively assessed through modulation transfer function (MTF) and bar pattern images. The edge enhancement visibility was assessed by measuring edge enhancement index (EEI) using the acrylic edge acquired images. A contrast detail (CD) phantom was utilized to compare detectability of simulated tumors, while an American College of Radiology (ACR) accredited phantom for mammography was used to compare detection of simulated calcification clusters. A custom-built phantom was employed to compare detection of fibrous structures. The PCD images were acquired at equal, and 30% less mean glandular dose (MGD) levels as of EID images. Observer studies along with contrast to noise ratio (CNR) and signal to noise ratio (SNR) analyses were performed for comparison of two detection systems. RESULTS: MTF curves and bar pattern images revealed an improvement of about 40% in the cutoff resolution with the PCD. The excellent spatial resolution offered by PCD system complemented superior detection of the diffraction fringes at boundaries of the acrylic edge and resulted in an EEI value of 3.64 as compared to 1.44 produced with EID image. At MGD levels (standard dose), observer studies along with CNR and SNR analyses revealed a substantial improvement of PCD acquired images in detection of simulated tumors, calcification clusters, and fibrous structures. At 30% less MGD, PCD images preserved image quality to yield equivalent (slightly better) detection as compared to the standard dose EID images. CONCLUSION: CdTe-based PCDs are technically feasible to image breast abnormalities (low/high contrast structures) at low radiation dose levels using the high energy inline phase sensitive imaging technique.

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