Lead bromide polycrystalline films were grown by the physical vapor deposition method (PVD). Glass 1"x1" in size, uncoated, and coated with Indium Tin Oxide (ITO), was used as substrate and rear contact. The starting material was evaporated at temperatures from 395°C to 530°C under high vacuum atmosphere (6 x 10 -3 Pa) and during 8 days. The substrate temperature was prefixed from 190°C to 220°C. Film thickness yielded values from 40 to 90 µm. Optical microscopy and scanning electron microscopy (SEM) were performed on the films. Grain size resulted to be from 1.0 to 3.5 µm. SEM and X-ray diffraction indicate that films grow with a preferred orientation with the (0 0 l) planes parallel to the substrate. The Texture Coefficient (TC) related to the plane (0 0 6) was 7.3. Resistivity values in the order of 10 12 Ωcm were obtained for the oriented samples, but a strong polarization indicates severe charge transport problems in the films. Film properties were correlated with the growth temperature and with previous results for films of other halides.
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.
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