Advances in physical vapor deposited polycrystalline-HgI2 X-ray imaging detectors

Physical Vapor Deposition deposited on A-Si TFT arrays, used for large area X-ray imaging detectors, reports improved properties for polycrystalline films of HgI2. X-ray diffraction shows 100% c-Axis orientation of the polycrystalline films. The electrical charge transport properties were found to be similar to those of single crystals. Transient charge transport (TCT) with alpha particles measurements was used to evaluate the mobility, the trapping time and the surface recombination velocity of the samples. Typical Electron-, and hole mobility of high quality polycrystalline HgI2 were mu(n) = 88 cm(2)/V .- s and mup = 4.1 cm(2)/V . s, respectively. Trapping times were tau(n) congruent to 18 mus and tau(p) congruent to 3.5 mus, and surface recombination velocities s(n) congruent to 1.4 x 10(5) cm/s and s(p) congruent to 3.7 x 10(3) cm/s. Bulk trapping-times and surface recombination velocities appear of the same order of magnitude as in the single crystal. The performances of these detectors as spectrometers in standard nuclear spectroscopy system were evaluated. We used a gamma source of Am-241 with a characteristic 59.6 keV gamma emission. The FWHM of the detector peaks depends on its charge transport properties. High quality polycrystalline HgI2 detector gives a photo peak with FWHM = 70 keV, while lower quality polycrystal line HgI2 detector doesn't give a photo peak at all.