Imaging performance of mercuric iodide polycrystalline films

Mercuric iodide (HgI₂) polycrystalline films have great potential as direct-conversion X-ray detectors for digital X-ray imaging. We have optimized a sublimation-based film growth process to create uniform films up to 6.5 × 6.5 cm² with very small (<25 μm) grain sizes on the readout side of the film. The growth techniques used can be easily extended to produce much larger film areas (>25 cm × 25 cm). Films grown on glass substrates uniformly coated with indium tin oxide (ITO) show low dark current and high sensitivity at low bias voltages: dark current of about 0.5 nA/cm² and corresponding X-ray response of about 20 μC/R cm² (bias 0.1 V/μm, X-ray tube settings 10 mA and 70 kVp, 2-mm Al filter). Additionally, films grown on patterned ITO on glass substrates showed a similar performance for pixel sizes of 10.2 to 4 mm². The imaging performance results of a film grown directly on a 6.5 × 6.5 (cm²) thin-film transistor array with 127 μm × 127 μm pixels are presented.