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

Abstract

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.

Crystal and Electronic Structures of Complex Bismuth Iodides A3Bi2I9 (A = K, Rb, Cs) Related to Perovskite: Aiding the Rational Design of Photovoltaics

“…In comparison, the optoelectronic properties of bismuth halides have been the focus of many fewer studies. The simple iodide BiI 3 has been investigated for applications such as hard radiation detection, 6-9 Xray imaging, [10][11][12] and for solar cells as hole transport material. 13 Recently, some of us have demostrated that BiI 3 can be used as the active layer in photovoltaic devices.…”

Growth of lead bromide polycrystalline films

“…Sodium iodide has been traditionally used for imaging, and structured films of cesium iodide are being developed as scintillators for such purpose [3]. Meanwhile, mercuric, lead and bismuth iodides are being developed as semiconductor detectors, whether as monocrystals for counting and spectrometry systems or as crystalline films for X-ray digital imaging [4][5][6][7][8][9]. The bromide family, with energy band gaps a bit wider than the iodide family ones, might be used as scintillators or semiconductors as well, depending on the cation.…”

“…However, and considering the total lack of knowledge about the growth of layers of the material, polycrystalline or oriented layers may be an intermediate step before growing epitaxial ones and will permit a first approach to the growth conditions. Taking into account that mercuric, lead and bismuth iodides polycrystalline and oriented films -due to several reasons [9] -have been grown by the physical deposition method (PVD), we consider interesting to know if lead bromide films could be grown by the same method.…”

Synthesis of mercuric iodide and bismuth tri‐iodide nanoparticles for heavy metal iodide films nucleation

“…Afterward, we sought for epitaxial films, studying nucleation and coalescence of these materials onto amorphous substrates [11]. This experience lead us to conclude that heavy metal iodide films exhibit two preferred growth orientations onto amorphous substrates such as floating glass, with their (00l) planes perpendicular or parallel to the substrate [10,12]. Also, we have found that the more oriented the film, lower is the dark current, and higher the sensitivity and the signal to dark relation of the detectors made with them [12].…”

“…Our group has gone through three stages in the development of films of heavy metal iodides for imaging applications: growth and characterization of polycrystalline films, nucleation by the physical vapor deposition method, and nanoparticles synthesis for nucleation. First, we grew and characterized polycrystalline films [8,9], and then partially oriented ones [3,10]. Afterward, we sought for epitaxial films, studying nucleation and coalescence of these materials onto amorphous substrates [11].…”