Bismuth tri-iodide polycrystalline films for X-ray direct and digital imagers

Bismuth tri-iodide films were grown by the physical vapor deposition method on gold-coated glass substrates 1 in.×1 in. (2.5×2.5 cm) in size. The growth was performed in a system especially designed and constructed for getting a fine control of the growth parameters. The best growth conditions were a source temperature of 350 °C, a growth temperature of 175 °C and a growth time of 24 h, with an initial pressure of 3×10−2 Pa. Film thicknesses and grain sizes gave values ranging between 5 and 60 μm (10%), and between 0.5 and 2 μm, respectively. The dark current density of the films is 9.7 pA/mm2 for an electric field of 5.6 V/μm, and the resistivity is 1.4×1013 Ω cm. Mobility-lifetime values of 3×10−7 cm2/V can be estimated for electrons. A signal to dark relation of 2.3 was measured at 250 mA and 40 KVp, with an electric field of 1 V/μm applied to the film.