Investigation of PbI<sub>2</sub> Film Fabricated by a New Sedimentation Method as an X-ray Conversion Material

Yun, Min; Cho, Sung-Ho; Lee, Rena; Jang, Gi-won; Kim, Yun-seok; Shin, Woon-jae; Nam, Sang-Hee

doi:10.1143/jjap.49.041801

Cited by 14 publications

(7 citation statements)

References 10 publications

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“…Moreover, it allows stable large area deposition without limits, such as the size of the vacuum chamber. There are two such methods: the sedimentation method and the screen printing method [5,6].…”

Section: Selection Of Fabrication Methodsmentioning

confidence: 99%

The development of efficient X-ray conversion material for digital mammography

Shin

Kim

et al. 2012

J. Inst.

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In this study, an experimental method based on theory is used to develop photoconductor that can replace the a-Se currently used as X-ray conversion layer in digital mammography. This is necessary because a-Se produced by the commercial fabrication method, of physical vapor deposition, has exhibited several problems when applied to digital mammography: instability due to crystallization and defect expansion due to high operating voltages, which is called the aging effect. Therefore, our work focused on developing a method of fabricating X-ray conversion films that do not suffer from crystallization and X-ray damage and optimizing the factors affecting the properties of the candidate photoconductors in order to acquire sufficient electrical signals to detect minute calcifications. The photoconductors were initially selected after the requirements for X-ray conversion materials, such as high atomic absorption, density, band-gap energy, work function, and resistivity, were examined. We selected HgI 2 , PbI 2 , and PbO because of their basic properties. Next, we experimentally investigated the performance of film samples fabricated by sedimentation and screen printing instead of physical vapor deposition. The structure of the X-ray conversion films (e.g., the thickness, electrodes, and blocking layer) were optimized for the application of a relatively low voltage to the X-ray conversion layer. The performance of the films were morphologically and electrically evaluated under mammography X-ray exposure conditions, and compared with those of a-Se films produced by physical vapor deposition. PbO appeared to be the most suitable alternative material because its electrical properties, such as the dark current, sensitivity, and signal-to-noise ratio (SNR), did not reveal the X-ray damage problem, and thus were maintained after repeated exposure to X-rays. Although PbO showed low sensitivity to X-ray exposure, its SNR was superior to that of the other materials, which is expected to improve its detective quantum efficiency, one of the factors used in evaluating images acquired by digital mammography.

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Section: Selection Of Fabrication Methodsmentioning

confidence: 99%

The development of efficient X-ray conversion material for digital mammography

Shin

Kim

et al. 2012

J. Inst.

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“…The grey hashed area represents the acceptable range for dark current in an FPXI. Data have been taken from various sources, including the following: a-Se ( i -layer and n-i-p ) from [ 15 ], a-Se ( n-i ) from [ 118 ], HgI 2 (PVD at 0.25 V/μm and SP) from [ 51 ], HgI 2 (PVD at 0.4 V/μm) from [ 122 ], PbI 2 (PVD) from [ 56 ], PbI 2 (SP) from [ 48 ], Cd 0.95 Zn 0.05 Te from [ 58 ], PbO (PVD) from [ 59 ], PbO (SP) from [ 123 ], PbBr 2 and HgBr 2 from [ 124 ] and BiI 3 from [ 125 ].…”

Section: Figurementioning

confidence: 99%

“…In addition to a-Se, there have been a number of other photoconductors, such as polycrystalline layers of TlBr [ 46 , 47 ], PbI 2 [ 48 , 49 ], HgI 2 [ 50 – 56 ], CdZnTe [ 57 , 58 ] and PbO [ 59 , 60 ], that have been investigated and some of these, in particular HgI 2 and PbO, have shown potential for use in commercial FPXI applications. Most of these photoconductors to date either suffer from possessing too large a dark current or not having sufficient charge collection efficiency.…”

Section: Introduction: Direct Conversion Flat Panel X-ray Imagersmentioning

confidence: 99%

Amorphous and Polycrystalline Photoconductors for Direct Conversion Flat Panel X-Ray Image Sensors

Kasap

Frey

Belev

et al. 2011

Sensors

400

326

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In the last ten to fifteen years there has been much research in using amorphous and polycrystalline semiconductors as x-ray photoconductors in various x-ray image sensor applications, most notably in flat panel x-ray imagers (FPXIs). We first outline the essential requirements for an ideal large area photoconductor for use in a FPXI, and discuss how some of the current amorphous and polycrystalline semiconductors fulfill these requirements. At present, only stabilized amorphous selenium (doped and alloyed a-Se) has been commercialized, and FPXIs based on a-Se are particularly suitable for mammography, operating at the ideal limit of high detective quantum efficiency (DQE). Further, these FPXIs can also be used in real-time, and have already been used in such applications as tomosynthesis. We discuss some of the important attributes of amorphous and polycrystalline x-ray photoconductors such as their large area deposition ability, charge collection efficiency, x-ray sensitivity, DQE, modulation transfer function (MTF) and the importance of the dark current. We show the importance of charge trapping in limiting not only the sensitivity but also the resolution of these detectors. Limitations on the maximum acceptable dark current and the corresponding charge collection efficiency jointly impose a practical constraint that many photoconductors fail to satisfy. We discuss the case of a-Se in which the dark current was brought down by three orders of magnitude by the use of special blocking layers to satisfy the dark current constraint. There are also a number of polycrystalline photoconductors, HgI2 and PbO being good examples, that show potential for commercialization in the same way that multilayer stabilized a-Se x-ray photoconductors were developed for commercial applications. We highlight the unique nature of avalanche multiplication in a-Se and how it has led to the development of the commercial HARP video-tube. An all solid state version of the HARP has been recently demonstrated with excellent avalanche gains; the latter is expected to lead to a number of novel imaging device applications that would be quantum noise limited. While passive pixel sensors use one TFT (thin film transistor) as a switch at the pixel, active pixel sensors (APSs) have two or more transistors and provide gain at the pixel level. The advantages of APS based x-ray imagers are also discussed with examples.

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“…Besides a-Se, there have been a number of other non-crystalline photoconductors, which have been investigated for use as X-ray-to-charge convertors in X-ray detectors 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 , although they are not yet mature enough for commercial use 19 . Polycrystalline Lead Oxide (PbO) holds a special place in this list since, similar to a-Se, it has been used previously in optical imaging, in so-called Plumbicon video pick-up tubes.…”

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confidence: 99%

Charge transport mechanism in lead oxide revealed by CELIV technique

Semeniuk

Juška

Oelerich

et al. 2016

Sci Rep

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Although polycrystalline lead oxide (PbO) belongs to the most promising photoconductors for optoelectronic and large area detectors applications, the charge transport mechanism in this material still remains unclear. Combining the conventional time-of-flight and the photo-generated charge extraction by linear increasing voltage (photo-CELIV) techniques, we investigate the transport of holes which are shown to be the faster carriers in poly-PbO. Experimentally measured temperature and electric field dependences of the hole mobility suggest a highly dispersive transport. In order to analyze the transport features quantitatively, the theory of the photo-CELIV is extended to account for the dispersive nature of charge transport. While in other materials with dispersive transport the amount of dispersion usually depends on temperature, this is not the case in poly-PbO, which evidences that dispersive transport is caused by the spatial inhomogeneity of the material and not by the energy disorder.

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Investigation of PbI₂ Film Fabricated by a New Sedimentation Method as an X-ray Conversion Material

Cited by 14 publications

References 10 publications

The development of efficient X-ray conversion material for digital mammography

The development of efficient X-ray conversion material for digital mammography

Amorphous and Polycrystalline Photoconductors for Direct Conversion Flat Panel X-Ray Image Sensors

Charge transport mechanism in lead oxide revealed by CELIV technique

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Investigation of PbI2 Film Fabricated by a New Sedimentation Method as an X-ray Conversion Material

Cited by 14 publications

References 10 publications

The development of efficient X-ray conversion material for digital mammography

The development of efficient X-ray conversion material for digital mammography

Amorphous and Polycrystalline Photoconductors for Direct Conversion Flat Panel X-Ray Image Sensors

Charge transport mechanism in lead oxide revealed by CELIV technique

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Investigation of PbI₂ Film Fabricated by a New Sedimentation Method as an X-ray Conversion Material