Near single-crystal electrical properties of polycrystalline HgI/sub 2/ produced by physical vapor deposition

Zuck, Asaf; Schieber, M.; Khakhan, O.; Burshtein, Z.

doi:10.1109/tns.2003.814544

Cited by 38 publications

(20 citation statements)

References 15 publications

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“…The ls for electrons in SP HgI 2 is in the range 10 À6 -10 À5 cm 2 /V [6,17], and the ls in PVD sample is about an order of magnitude greater (Table 1). Recently, it has been reported that the ls for electrons in PVD HgI 2 is in the range 10 À5 -10 À4 cm 2 /V, which is almost equal to that of single crystal HgI 2 [20,21]. The reason is that a PVD HgI 2 layer grows in a columnar structure perpendicular to the substrate.…”

Section: Mercuric Iodide (Hgi 2 )mentioning

confidence: 99%

Recent advances in X-ray photoconductors for direct conversion X-ray image detectors

Kasap

Kabir

Rowlands

2006

Current Applied Physics

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Section: Mercuric Iodide (Hgi 2 )mentioning

confidence: 99%

Recent advances in X-ray photoconductors for direct conversion X-ray image detectors

Kasap

Kabir

Rowlands

2006

Current Applied Physics

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“…The high gain materials under investigation include HgI 2 , PbI 2 , and PbO. [7][8][9][10][11][12] Another approach involves the use of a double layer of a-Se photoconductive material. While a thicker top layer acts as the converter of X rays into electrons and holes, a thinner bottom layer provides further signal amplification by means of an avalanche multiplication mechanism.…”

Section: Introductionmentioning

confidence: 99%

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

El‐Mohri¹,

Antonuk²,

Koniczek³

et al. 2009

Medical Physics

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Active matrix, flat-panel imagers ͑AMFPIs͒ employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and/or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel ͑AP͒ architectures, using polycrystalline-silicon ͑poly-Si͒ TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n-and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array ͑PSI-1͒ that employs a pixel architecture with a single TFT, as well as two arrays ͑PSI-2 and PSI-3͒ that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of ϳ10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical fill factors that are close to unity. In addition, the greater complexity of PSI-2 and PSI-3 pixel circuits, compared to that of PSI-1, has no observable effect on spatial resolution. Both PSI-2 and PSI-3 exhibit high levels of additive noise, resulting in no net improvement in the signal-to-noise performance of these early prototypes compared to conventional AMFPIs. However, faster readout rates, coupled with implementation of multiple sampling protocols allowed by the nondestructive nature of pixel readout, resulted in a significantly lower noise level of ϳ560 e ͑rms͒ for PSI-3.

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“…, Hunt et al 2007 Another strategy for improving SNR, and thereby DQE performance, of direct detection AMFPIs involves the use of photoconductive materials, such as Pbl 2 , HgI 2 and PbO, which provide significantly higher signal per unit of absorbed x-ray energy than that of the a-Se photoconductors currently used in commercial direct detection devices. (Street et al 2002, Zentai et al 2007, Zuck et al 2003, Hartsough et al 2004, Simon et al 2005 As is the case for a-Se, there is no reported fundamental limitation on the maximum area for any of these photoconductive materials. HgI 2 , in particular, exhibits a number of interesting properties, making it an attractive candidate.…”

Section: Introductionmentioning

confidence: 99%

Signal behavior of polycrystalline HgI₂at diagnostic energies of prototype, direct detection, active matrix, flat-panel imagers

Antonuk

El‐Mohri

et al. 2008

Phys. Med. Biol.

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Active matrix, flat-panel x-ray imagers based on a-Si:H thin film transistors offer many advantages and are widely utilized in medical imaging applications. Unfortunately, the detective quantum efficiency (DQE) of conventional flat-panel imagers incorporating scintillators or a-Se photoconductors is significantly limited by their relatively modest signal to noise ratio, particularly in applications involving low x-ray exposures or high spatial resolution. For this reason, polycrystalline HgI 2 is of considerable interest by virtue of its low effective work function, high atomic number, and the possibility of large-area deposition. In this study, a detailed investigation of the properties of prototype, flat-panel arrays coated with two forms of this high-gain photoconductor are reported. Encouragingly, high x-ray sensitivity, low dark current, and spatial resolution close to the theoretical limits were observed from a number of prototypes. In addition, input-quantum-limited DQE performance was measured from one of the prototypes at relatively low exposures. However, high levels of charge trapping, lag, and polarization, as well as pixel-to-pixel variations in x-ray sensitivity are of concern. While the results of the current study are promising, further development will be required to realize prototypes exhibiting the characteristics necessary to allow practical implementation of this approach.

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Near single-crystal electrical properties of polycrystalline HgI/sub 2/ produced by physical vapor deposition

Cited by 38 publications

References 15 publications

Recent advances in X-ray photoconductors for direct conversion X-ray image detectors

Recent advances in X-ray photoconductors for direct conversion X-ray image detectors

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

Signal behavior of polycrystalline HgI₂at diagnostic energies of prototype, direct detection, active matrix, flat-panel imagers

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Near single-crystal electrical properties of polycrystalline HgI/sub 2/ produced by physical vapor deposition

Cited by 38 publications

References 15 publications

Recent advances in X-ray photoconductors for direct conversion X-ray image detectors

Recent advances in X-ray photoconductors for direct conversion X-ray image detectors

Active pixel imagers incorporating pixel‐level amplifiers based on polycrystalline‐silicon thin‐film transistors

Signal behavior of polycrystalline HgI2at diagnostic energies of prototype, direct detection, active matrix, flat-panel imagers

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Signal behavior of polycrystalline HgI₂at diagnostic energies of prototype, direct detection, active matrix, flat-panel imagers