Examination of PbI₂ and HgI₂ photoconductive materials for direct detection, active matrix, flat-panel imagers for diagnostic X-ray imaging

In this paper, the results of empirical studies of the dark current and X-ray signal response of thick, polycrystalline films of lead iodide (FbI ₂) and mercuric iodide (HgI₂) are reported. These studies are being carried out as part of an extensive, integrated program of research to develop and incorporate such photoconductive, X-ray detection materials into direct detection, active matrix flat-panel imagers (AMFPIs) for applications in diagnostic imaging, as well as for radiotherapy imaging. Simple detector configurations incorporating these materials were prepared by physical vapor deposition (PVD) with thicknesses ranging from approximately 90 to 500 μm. For these detectors, the temporal behavior of the dark current and of the X-ray-induced photocurrent, under irradiation conditions relevant to fluoroscopy, radiography and mammography, were quantitatively examined and are reported. In addition, X-ray sensitivity results are also presented for a variety of conditions. The measurements were performed for externally applied electric fields ranging from 0.2 to 2.0 V/μm for both negative and positive polarities.