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Bismuth tri-iodide polycrystalline films were grown by the physical vapor deposition method. Glass 1 1 in size was used as the substrate. Palladium was deposited previously onto the substrates as the rear contact. For growth, bismuth tri-iodide 99.999% was heated at 130-170 C under high vacuum atmosphere (5 10 5 mmHg) or under Ar pressure for 20 hours. Film thickness was measured by the transmission of 59.5 keV 241 Am emission, giving values ranging from 90 to 130 m (5%). Film grain size was measured by scanning electron microscopy, and it gave an average of (50 20) m. Detectors were made with the films by depositing palladium as the front contact (contact area 4 mm 2 )and then performing acrylic encapsulation. Resistivities of 6 10 12 .cm and current densities of 240 pA/cm 2 at 20 V were obtained for these detectors. The electron mobility and lifetime and the electron mobility-lifetime product were measured by the transient charge technique, which gave values of 4.4 cm 2 /V.s, 3 3 10 7 s and 1 4 10 6 cm 2 /V respectively. X-ray film response was checked by irradiating the films with a 241 Am source and with an X-ray beam, for different beam energies and intensities and for several bias voltages applied to the detector. A linear response with exposure rate was obtained. Finally, the results were compared with previous ones for monocrystals of bismuth tri-iodide and polycrystalline films of alternative materials like lead iodide and mercuric iodide.Index Terms-Bismuth tri-iodide, compound semiconductor films, X-ray imaging.

Lead iodide purified by zone refining and repeated sublimation was used for growing Polycrystalline films by physical vapor deposition. Palladium film was deposited as rear contact onto glass and alumina substrates 2.5 x 2.5 cm 2 in size. Onto it, lead iodide polycrystalline films were grown by sublimation at 390 °C and 5 x 10 -5 mm Hg, substrate temperatures of about 200 °C and deposition times of about 10 days. Film thickness was measured by X-ray transmission at 59.5 keV giving values from 35 to 50 µm (5%). Optical and atomic force microscopy were performed to the films giving an average grain size of (80±20) µm. Low temperature photoluminescence was performed and peak position and broadness confirmed the high purity of starting materials. Films were characterized by X-ray diffraction, giving an [ΣI (0 0 l)] / [ΣI (h k l)] relation of 0.8 that indicates a strong growth preferred orientation along c axis. Front palladium thermal deposition contacts and acrylic encapsulation were done and apparent resistivity (2 x 10 14 Ω . cm) and current density (7 pA/cm 2 (30 V)) were obtained. X-ray film response was checked by irradiating with 241 Am and an X-ray beam. Finally, film and detector characterizations were correlated with starting material, deposition parameters and previous results for the same and alternative materials like mercuric iodide.