The polarization mechanism in CdTe Schottky detectors

Cola, A.; Farella, I.

doi:10.1063/1.3099051

Cited by 115 publications

(100 citation statements)

References 13 publications

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“…Polarization increases the higher the photon flux [20]. Hence many experiments and theoretical calculation were done to understand this problem focussing on a large lifetime of electrons and holes, the influence of Te-inclusions and -precipitates [21][22][23]. However, these investigations were restricted to low flux only.…”

Section: Introductionmentioning

confidence: 99%

CdTe/CZT under high flux irradiation

Straßburg¹,

Schroeter²,

Hackenschmied³

2011

J. Inst.

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Direct converting quantum counting detectors based on cadmium telluride and cadmium zinc telluride have been investigated with respect to their properties under intense X-ray irradiation. To derive a detailed picture of the performance of such detectors, the influence of the electric field, the detector thickness, the temperature and the intensity of the X-ray irradiation was studied. The results are discussed in terms of the "polarization" phenomenon, a reduction of the electric field strength inside the detector due to immobile charge carriers accumulating during irradiation. Furthermore, the impact of Te-inclusions and -precipitates is presented.

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Section: Introductionmentioning

confidence: 99%

CdTe/CZT under high flux irradiation

Straßburg¹,

Schroeter²,

Hackenschmied³

2011

J. Inst.

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“…Degradations occur more rapidly at high temperatures, at low bias voltages and for thick detectors, as widely shown in several works [10,[12][13][14][15][16][17]. Several solutions have been proposed to suppress polarization: high bias voltage operation, low temperature, low detector thickness, and switching off the bias voltage at regular time intervals.…”

Section: Introductionmentioning

confidence: 99%

Electrical characterization of CdTe pixel detectors with Al Schottky anode

Turturici

Abbene

Gerardi

et al. 2014

Nuclear Instruments and Methods in Physics Research Section A:

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a b s t r a c tPixelated Schottky Al/p-CdTe/Pt detectors are very attractive devices for high-resolution X-ray spectroscopic imaging, even though they suffer from bias-induced time instability (polarization). In this work, we present the results of the electrical characterization of a (4 Â 4) pixelated Schottky Al/p-CdTe/Pt detector. Current-voltage (I-V) characteristics and current transients were investigated at different temperatures. The results show deep levels that play a dominant role in the charge transport mechanism. The conduction mechanism is dominated by the space charge limited current (SCLC) both under forward bias and at high reverse bias. Schottky barrier height of the Al/CdTe contact was estimated by using the thermionic-field emission model at low reverse bias voltages. Activation energy of the deep levels was measured through the analysis of the reverse current transients at different temperatures. Finally, we employed an analytical method to determine the density and the energy distribution of the traps from SCLC current-voltage characteristics.

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“…9 Typical CdTe sensor thicknesses for imaging detectors range from 1 mm to 3 mm and thanks to their wide bandgap and extremely high resistivity (> 10 9 Ωcm), the sensors can be operated in ohmic mode already at room temperature -with beneficial results on the polarization effect. 10,11 Due to the higher ls-product of electrons with respect to holes, the detectors are operated in electron-collection mode and virtually all the charge is collected by the front-end electronics. The small aspect ratios bring further benefits in virtue of the small pixel effect.…”

Section: A Sensor Materialsmentioning

confidence: 99%

Assessment of the spectral performance of hybrid photon counting x‐ray detectors

Trueb¹,

Zambon²,

Broennimann³

2017

Medical Physics

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Purpose: Hybrid Photon Counting (HPC) detectors profoundly improved x-ray diffraction experiments at third generation synchrotron facilities. Enabling the simultaneous measurement of x-ray intensities in multiple energy bins, they also have many potential applications in the field of medical imaging. A prerequisite for this is a clean spectral response. To quantify how efficiently HPC detectors are able to assign photons to the correct energy bin, a quantity called Spectral Efficiency (SE) is introduced. This figure of merit measures the number of x-rays with correctly assigned energy normalized to the number of incoming photons. Methods: A prototype HPC detector has been used to perform precision measurements of x-ray spectra at the BESSY synchrotron. The detector consists of a novel ASIC with pixels of 75 9 75 lm 2 size and a 750 lm thick CdTe sensor. The experimental data are complemented by the results of a Monte-Carlo (MC) simulation, which not only includes the physical detection process but also pulse pile-up at high photon fluxes. The spectra and the measured photon flux are used to infer the Spectral Efficiency. Results: In the energy range from 10 to 60 keV, both the Quantum Efficiency and the Spectral Efficiency were precisely measured and simulated. Good agreement between simulation and experiment has been achieved. For the small pixels of the prototype detector, a SE between 15% and 77% has been determined. The MC simulation is used to predict the SE for various pixel sizes at different photon fluxes. For a typical flux of 5•10 7 photons/mm 2 /s used in human Computed Tomography (CT), the highest SE is achieved for pixel sizes in the range between 150 9 150 lm 2 and 300 9 300 lm 2 . Conclusions: The Spectral Efficiency turns out to be a useful figure of merit to quantify the spectral performance of HPC detectors. It allows a quantitative comparison of detectors with different sensor and ASIC configurations over a broad range of x-ray energies and fluxes. The maximization of the SE is a prerequisite for a successful usage of HPC detectors in the field of medical imaging.

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The polarization mechanism in CdTe Schottky detectors

Cited by 115 publications

References 13 publications

CdTe/CZT under high flux irradiation

CdTe/CZT under high flux irradiation

Electrical characterization of CdTe pixel detectors with Al Schottky anode

Assessment of the spectral performance of hybrid photon counting x‐ray detectors

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