Electronic and thermal properties of magnesium‐doped a‐Se films

Dash, Isha; Tonchev, D.; Belev, George; Mani, H.; Kasap, S. O.

doi:10.1002/pssc.200881283

Cited by 4 publications

(2 citation statements)

References 6 publications

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“…Such terminology is useful and convenient but must be used with care since the Fermi level in a-Se is near the center of the bandgap, and cannot be easily shifted by doping as in crystalline semiconductors. The required properties are obtained by changing the deep trap concentrations by suitably alloying and doping a-Se with the result that either injected holes or injected electrons are deeply trapped [ 80 , 116 , 117 ].…”

Section: Dark Currentmentioning

confidence: 99%

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

Kasap

Frey

Belev

et al. 2011

Sensors

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399

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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Section: Dark Currentmentioning

confidence: 99%

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

Kasap

Frey

Belev

et al. 2011

Sensors

Self Cite

399

326

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“…The most straightforward way of introducing an impurity into a-Se is through synthesis of Selenium alloys or doping [93]- [95]. Recently, Chowdhury's group has synthesized a high resistivity a-Se (As, Cl) alloy through a custom deposition setup [96].…”

Section: Impuritiesmentioning

confidence: 99%

Recent Developments of Amorphous Selenium-Based X-Ray Detectors: A Review

Huang

Abbaszadeh

2020

IEEE Sensors J.

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Amorphous selenium (a-Se) is a photoconductive material that has been intensively investigated from its early application in xerography to its present application in flat panel X-ray imagers. It can be deposited up to a few millimeters thick over a large area. Its high vapor pressure yields uniform coverage in novel device structures for lowcost and large-area applications. The evidence of avalanche multiplication in a-Se and application of a-Se in high-gain avalanche rushing photoconductor video-tubes goes back to the early 1980s. Over the past decade there has been increasing research interest in novel detector structures and integration of a-Se with new materials to leverage the avalanche properties. We summarize some of the shortcomings of a-Se such as low charge carrier mobility, low charge conversion efficiency, depth dependence, and high dark current at high electric fields. We then highlight recent developments in a-Se-based devices to address these shortcomings and enable picosecond timing performance and high detection efficiency.

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Doped and Stabilized Amorphous Selenium Single and Multilayer Photoconductive Layers forX‐Ray Imaging Detector Applications

Kasap¹

2022

Photoconductivity and Photoconductive Materials

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Electronic and thermal properties of magnesium‐doped a‐Se films

Cited by 4 publications

References 6 publications

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

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

Recent Developments of Amorphous Selenium-Based X-Ray Detectors: A Review

Doped and Stabilized Amorphous Selenium Single and Multilayer Photoconductive Layers forX‐Ray Imaging Detector Applications

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