Perspectives of the heavy metal halides family for direct and digital X-ray imaging

Films of heavy metal halides (mercuric iodide, lead iodide, bismuth tri-iodide, lead bromide, mercuric bromide and mercuric bromide-iodide), 1"×1" and 2"×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 [001] 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.