This paper reports the growth of bismuth tri-iodide thick films intended for direct and digital X-ray imaging. Films were grown by the vertical physical vapor deposition method, onto glass substrates 2"x 2" in size, with gold previously deposited as rear electrode. The film thickness was up to 33 µm (±5 %). Optical microscopy and SEM were performed on the films and grain size resulted to be up to 40 µm. A strong correlation was found between the microcrystals growth orientation and the growth temperature. At low temperatures, microcrystals grow with their c axis parallel to the substrate, whereas at higher temperatures, they grow with their c axis perpendicular to the substrate. The higher the growth temperature, the lower the dark current of the film, and the higher the resistivity, which was from 10 13 to 10 15 Ωcm. A sensitivity to X-rays of 6.9 nC/R.cm 2 was measured irradiating the films with X-rays from a mamographer. Film properties were correlated with the growth temperature, with previous results for bismuth tri-iodide films and monocrystals and with data for films of alternative materials such as lead and mercuric iodide.

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Films of heavy metal halides (mercuric iodide, lead iodide, bismuth tri-iodide, lead bromide, mercuric bromide and mercuric bromide-iodide), 1" x 1" and 2" x 2" in area, have been grown by physical vapor deposition onto alumina and glass substrates with conductive coatings. From the point of view of film growth the materials was found to have similar behavior, which was evaluated by studying grain size and texture of the films as a function of growth temperature. Films grow oriented with the (0 0 l) crystalline planes parallel or perpendicular to the substrate, according to X-ray diffraction. The influence of film orientation on electrical properties and on response to radiation was evaluated by measuring resistivity and response to X-rays. All the layers give good linearity of response to an X-ray beam. The sensitivity of the layers (signal to dark relation / exposure rate) is maximum (1380) for mercuric iodide. For all the materials, the more oriented the films, the lowest the dark current, and the higher the sensitivity and the signal/dark relation. A superior correlation between electrical and response properties and the layer orientation can be deduced for films of the family of heavy metal halides, observed as a whole.