Electronic transport and optical measurements in polycrystalline Pbl 2 are reported as part of a study to evaluate the material for large area x-ray imaging applications. The films are deposited by vacuum evaporation with thickness 20-100 m and have grain sizes of up to 10 m. The room temperature hole drift mobility measured by time-of-flight is 2ϫ10 Ϫ2 -1.5ϫ10 Ϫ1 cm 2 /V s, depending on the specific sample, with an activation energy of 0.25 eV. Hole charge collection measurement gives about 10 Ϫ6 cm 2 /V for the mobility-lifetime product. Details of the electron transport were not determined in this study because the mobility is too small. The hole transport is discussed in terms of a trapping model with either a discrete level above the valence band or a disorder-induced band tail. Optical absorption, photoconductivity, and Hall effect measurements are also reported.
In this paper, we discuss recent progress that has been made in the development of high resolution X-ray imaging detectors using photoconducting films oflead iodide (Pb12). Pb12 is a wide bandgap semiconductor with high X-ray stopping efficiency. We have been investigating thick films of lead iodide which can be prepared in large areas in a cost effective manner. These fihns can be coupled to readout technologies such as amorphous silicon flat panel arrays and vidicon tubes to produce X-ray imaging detectors for applications such as mammography, fluoroscopy, X-ray diffraction and non-destructive evaluation. Recent results obtained when these Pb12 films are coupled to 512 x 512 flat panel a-Si:H array are reported. This includes dark current, signal and resolution measurements. Properties of lead iodide films which are relevant to imager performance are also discussed.
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