Skip to Main Content
Use of physical vapor deposition (PVD) of polycrystalline HgI2 films on Si-TFT arrays brought about a breakthrough in the use of HgI2 for large area pixellated X-ray imaging. Latest advances in the deposition process led to full-texture high-density films, with highly orientated crystallites, as evidenced for example by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The good structural data also yielded excellent electrical charge transport properties, which approached those of single crystals. Transient charge transport (TCT) with alpha-particle near-surface absorption was used to measure carrier mobility, trapping time, and surface recombination velocity for each sample. Typical electron and hole mobility of high quality polycrystalline HgI2 films were μn = 88 cm2/V · s and μp = 4.1 cm2/V · s, respectively. Trapping times were τn ≅ 18 μs and τp ≅ 3.5 μs, and surface recombination velocities sn ≅ 1.4 × 105 cm/s and sp ≅ 3.7 × 103 cm/s. The performance of these detectors as spectrometers in a standard nuclear spectroscopy system was evaluated. We used a gamma source of 241Am with the characteristic 59.6 keV gamma photo-peak. The full width at half maximum (FWHM) of the detector photo peak depended on its charge transport properties. High quality polycrystalline HgI2 film detectors yield a peak of approximately 38 keV FWHM, while lower quality ones yield a much broader peak of FWHM > 70 keV. Such widths are still inferior to those of a single crystal (typically ∼5 keV), yet the results suggest that further improvement through optimization of manufacturing conditions is possible. The talk reviews our past efforts, recent new results, and plans for the future.