Correlation between growth orientation and growth temperature for bismuth tri-iodide films

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 mum (+/-5 %). Optical microscopy and SEM were performed on the films and grain size resulted to be up to 40 gm. 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) Omegacm. 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. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.