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.

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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.

This paper describes the preliminary results obtained from our study of optical and electrical properties of BiT3 crystals. The bismuth iodine polycrystals were grown using commercial starting material by vertical Bridgman method. For our measurements we used only single crystal samples that were cut out from grown crystals perpendicular to C6-axis. BiT3 is a layered hexagonal lattice similar to the Pb12 lattice, where two-thirds of the metal sublattice sites are occupied and the remaining one-third are vacant. The average atomic number of the bismuth iodide ((Z) = 60.5) is very close to that of lead iodide ((Z) = 62.7). Therefore, Bi13 is similar to the better known Pb12 and can be a promising detector material. Our measurements have shown that bismuth iodide crystals have resistivity on the order of 1 Gcm and energy gap Eg 1.72eV. The photocurrent, as a function of bias and wavelength, as well as detector responses from excitation by blue LED and X-ray tube photons were measured. The value of the mobility-lifetime product of the electron (rc l05cm2/V) was estimated by the Hecht technique. The optical characterization also included measuring of quantum efficiency for BiT3 detector. The experimental results demonstrate the potential feasibility of using BiT3 as detector material operating at room temperatures.

This paper describes our recent research in developing vacuum sublimed lead iodide films for X-ray imaging. Lead iodide films are promising for this application due to their low dark current, high stopping efficiency, reasonably good charge transport, low cost, and relatively easy scale-up. Lead iodide films (up to 5 × 5 cm2 area) have been grown and characterized by measuring their X-ray imaging properties such as spatial resolution, and contrast transfer function. Excellent spatial resolution (> 10 lp/mm with high CTF ≈50%) has been recorded with PbI2 films. Relevant detection properties such as signal amplitude for given X-ray energy has also been measured and was found to be about 10 times larger as compared to standard phosphor screens used for X-ray imaging. Charge transport and timing characteristics of these films have been measured and the results indicate that these films should be capable of real-time operation. Application of these films for X-ray imaging such as mammography, fluoroscopy, and X-ray diffraction is addressed.