Comparison of PbI2 and HgI2 for direct detection active matrix x-ray image sensors

Abstract

Articles you may be interested inScintillator high-gain avalanche rushing photoconductor active-matrix flat panel imager: Zero-spatial frequency xray imaging properties of the solid-state SHARP sensor structure Med. Phys. 39, 7102 (2012); 10.1118/1.4760989 2 ∕ 3 in. ultrahigh-sensitivity image sensor with active-matrix high-efficiency electron emission device J. Vac. Sci. Technol. B 28, C2D11 (2010); 10.1116/1.3271163 High dynamic range active pixel sensor arrays for digital x-ray imaging using a -Si : H J. Vac. Sci. Technol. A 24, 850 (2006); 10.1116/1.2192526 X-ray detection by direct modulation of an optical probe beam-Radsensor: Progress on development for imaging applications Rev. Sci. Instrum. 75, 3995 (2004); 10.1063/1.1790055X-ray-induced recombination effects in a-Se-based x-ray photoconductors used in direct conversion x-ray sensors J.The factors determining the x-ray sensitivity of HgI 2 and PbI 2 as direct detector materials for large area matrix addressed x-ray image sensors are described, along with a model to explain their different properties. The imaging studies are made on test arrays with 512ϫ512 pixels of size 100 m. The x-ray sensitivity and spatial resolution are reported, along with measurements of the various mechanisms that influence the sensitivity, such as charge collection, x-ray absorption, fill factor, and image lag. The spatial resolution of PbI 2 decreases with increasing film thickness, but this effect is not observed in HgI 2 . The x-ray response data are used to compare the sensitivity to the theoretical values for the ionization energy and to identify the various loss mechanisms. We find that the sensitivity of HgI 2 can be explained by a few small and well characterized loss factors. This material exhibits good spatial resolution, high fill factor, and high charge collection. PbI 2 films exhibit lower sensitivity, principally attributable to a very large image lag. We propose that the x-ray response of the two materials is distinguished by their different depletion layer properties, and present a model that accounts for the sensitivity, image lag, and spatial resolution of PbI 2 .

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

“…(Su et al 2005) Moreover, recent investigations of polycrystalline HgI 2 have demonstrated that this material offers an attractively low effective work function, W EFF -(In the present context, W EFF is defined as the average amount of absorbed x-ray energy required to generate one unit of detected pixel charge.) Values for W EFF of ~5 eV have been reported for polycrystalline HgI 2 (Su et al 2005, Street et al 2002 at far lower electric field strengths (less than 1 V/μm) than the ~10 V/μm required to obtain a W EFF of ~50 eV for a-Se. Thus, a far thinner layer of HgI 2 can be used to detect a given fraction of incident x rays, and at a much lower electric field, compared to an a-Se detector.…”

“…, 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.…”

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

“…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.…”

Perovskite Solar Cells: Device Construction andI-VHysteresis

“…将该极化的分 子引入钙钛矿晶体结构中很可能导致自发极化的形成: 外加电场导致的 MA ＋ 的偶极取向和晶格扭曲极有可能 影响载流子的传输动力. 包括 PbI 2 (本身是一种探测器 材料 [43] )在内, 金属卤化物通常受到光激发都会导致形 成卤素的空位, 并且在外加偏压的作用下重新分布, 从 而形成内建电场 [34] . 由于离子的极化形成位移导致产生的电荷间的库 伦作用会被增强, 并可以更有效地分离光生电子空穴 对.…”