X-ray sensitivity of a-Se for x-ray imaging with electrostatic readout

Kasap, S. O.; Aiyah, Viswanath; Polischuk, B.; Baillie, A.

doi:10.1063/1.367074

Cited by 14 publications

(9 citation statements)

References 35 publications

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“…These data correspond to the intrinsic pair creation energy implying that the electron-hole pair generation and collection is not mediated by recombination or incomplete energy absorption (such as Compton scattering). The theoretical values of W 0 ± agree with those measured experimentally for a-Se: W 0 ± = 4-6 eV [11], 6 eV [41,42], 5.4 eV [43]. The results of our detailed calculations are remarkably close to those obtained using the approximate equation 3that explains the success of Que and Rowlands [9] analysis of x-ray photogeneration in a-Se with the assumption that E g = E th .…”

Section: Pair Creation Energysupporting

confidence: 84%

Modeling the radiation ionization energy and energy resolution of trigonal and amorphous selenium from first principles

Izadi-Darbandi¹,

Devoie²,

Matteo³

et al. 2012

J. Phys.: Condens. Matter

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Advances in the development of amorphous selenium-based direct conversion photoconductors for high-energy radiation critically depend on the improvement of its sensitivity to ionizing radiation, which is directly related to the pair production energy. Traditionally, theories for the pair production energy have been based on the parabolic band approximation and do not provide a satisfactory agreement with experimental results for amorphous selenium. Here we present a calculation of the pair creation energy in trigonal and amorphous selenium based on its electronic structure. In indirect semiconductors, such as trigonal selenium, the ionization threshold energy can be as low as the energy gap, resulting in a lower pair creation energy, which is a favorable factor for sensitivity. Also, the statistics of photogenerated charge carriers is studied in order to evaluate the theoretical value of the Fano factor and its dependence on recombination processes. We show that recombination can significantly compromise the detector's energy resolution as a result of an increase in the Fano factor.

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Section: Pair Creation Energysupporting

confidence: 84%

Modeling the radiation ionization energy and energy resolution of trigonal and amorphous selenium from first principles

Izadi-Darbandi¹,

Devoie²,

Matteo³

et al. 2012

J. Phys.: Condens. Matter

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“…The EHP creation energy W ± in a-Se has a strong dependence on the electric field and weak dependence on the x-ray photon energy [23,24]. The quantity W ± decreases with increasing electric field and photon energy.…”

Section: Resultsmentioning

confidence: 97%

Description of the cohomology of Banach algebras and locally convex algebras in the language of $ A_\infty$-structures

Smirnov¹,

Kuznetsova²,

Mayorova³

1998

Izv. Math.

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A cascaded linear system model that includes incomplete charge collection and interaction-depth dependent conversion gain and charge collection stages is considered for the calculation of the zero spatial frequency detective quantum efficiency, DQE(0), of a direct conversion x-ray image detector. The model includes signal and noise propagations in the following stages:(1) x-ray attenuation, (2) conversion gain, (3) charge collection, and (4) addition of electronic noise. The primary x-ray photon interaction and also the secondary K-fluorescent photon interaction are included in determining the interaction-depth dependent conversion gain across the photoconductor. We examine DQE(0) of a-Se detectors for fluoroscopic applications as a function of photoconductor thickness with varying amounts of electronic noise and x-ray exposure under (a) constant field, and (b) constant voltage operating conditions. We show that there is an optimum photoconductor thickness, which maximizes DQE(0) under a constant voltage operation. The optimum thickness depends on the added electronic noise, x-ray exposure, charge collection efficiency and bias voltage. For the quantities mentioned above that are appropriate for a-Se detectors and fluoroscopic applications, the optimum a-Se thickness is ∼700 µm and the corresponding DQE is ∼0.4. It is shown that the DQE depends strongly on the charge transport properties of the photoconductors. With the radiation-receiving electrode negatively biased, the DQE is more dependent on electron lifetime (τ e ) than hole lifetime (τ h ). Full electron trapping, (τ e = 0) reduces the DQE by about 73.3% at the detector thickness of 1000 µm whereas full hole trapping (τ h = 0) reduces the DQE by about 43.7%. The DQE for the negative bias is lower than for the positive bias, and the difference in DQE, as expected, increases with the photoconductor thickness because of the asymmetric transport properties of holes and electrons in a-Se. The present results show that the DQE generally does not continue to improve with greater photoconductor thickness because of charge carrier trapping effects. The DQE of a polyenergetic x-ray beam is only slightly lower than a monoenergetic x-ray beam with the same average photon energy. The theoretical model shows a very good agreement with the experimental DQE versus exposure characteristics published in the literature.

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“…To the best of our knowledge, the only photoconductor whose X-ray energy dependency on W ± has been examined (both experimentally [31,41,[50][51][52] and theoretically [34,35,37,[53][54][55]) is a-Se. As was discussed in [34] (and references therein), within the framework of the geminate recombination model, the initial separation between an electron and a hole controls the probability of their escape from recombination.…”

Section: X-ray Energy Dependencymentioning

confidence: 99%

The X-ray Sensitivity of an Amorphous Lead Oxide Photoconductor

Grynko

Thibault

Pineau

et al. 2021

Sensors

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The photoconductor layer is an important component of direct conversion flat panel X-ray imagers (FPXI); thus, it should be carefully selected to meet the requirements for the X-ray imaging detector, and its properties should be clearly understood to develop the most optimal detector design. Currently, amorphous selenium (a-Se) is the only photoconductor utilized in commercial direct conversion FPXIs for low-energy mammographic imaging, but it is not practically feasible for higher-energy diagnostic imaging. Amorphous lead oxide (a-PbO) photoconductor is considered as a replacement to a-Se in radiography, fluoroscopy, and tomosynthesis applications. In this work, we investigated the X-ray sensitivity of a-PbO, one of the most important parameters for X-ray photoconductors, and examined the underlying mechanisms responsible for charge generation and recombination. The X-ray sensitivity in terms of electron–hole pair creation energy, W±, was measured in a range of electric fields, X-ray energies, and exposure levels. W± decreases with the electric field and X-ray energy, saturating at 18–31 eV/ehp, depending on the energy of X-rays, but increases with the exposure rate. The peculiar dependencies of W± on these parameters lead to a conclusion that, at electric fields relevant to detector operation (~10 V/μm), the columnar recombination and the bulk recombination mechanisms interplay in the a-PbO photoconductor.

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X-ray sensitivity of a-Se for x-ray imaging with electrostatic readout

Cited by 14 publications

References 35 publications

Modeling the radiation ionization energy and energy resolution of trigonal and amorphous selenium from first principles

Modeling the radiation ionization energy and energy resolution of trigonal and amorphous selenium from first principles

Description of the cohomology of Banach algebras and locally convex algebras in the language of $ A_\infty$-structures

The X-ray Sensitivity of an Amorphous Lead Oxide Photoconductor

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