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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 .