Comparative Study of HgI 2 , PbI 2 and TlBr Films Aimed for Ionizing Radiation Detection in Medical Imaging
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Comparative Study of HgI2, PbI2 and TlBr Films Aimed for Ionizing Radiation Detection in Medical Imaging Marcelo Mulato1, José F. Condeles2, Julio C. Ugucioni1, Ademar M. Caldeira-Filho1 and Natalia Destefano1. 1 Department of Physics, University of São Paulo, Ribeirão Preto-SP Brazil 2 Department of Physics, Universidade Federal do Triângulo Mineiro, Uberaba-MG, Brazil
ABSTRACT Wide bandgap semiconductor films were obtained by spray pyrolysis, thermal evaporation and casting. These films were characterized under similar conditions in order to compare their structures, surface morphology and photocurrent properties. All films show either a crystalline or a polycrystalline structure. SEM pictures of sprayed films present holes and fissures and non-total covering of the substrate. The photoresponse was obtained for evaporated TlBr films, HgI2 casted with polystyrene (PS) scaffold, sprayed and evaporated PbI2 films. The photo to dark current ratio is discussed as well as the difference of photo to dark current at an electric field of 100 V/cm. The discussion also focuses on a future optimized material. INTRODUCTION Wide bandgap semiconductors, like thallium bromide (TlBr), mercuric iodide (HgI2) and lead iodide (PbI2) have been investigated in last years for X-ray and Ȗ-ray detectors in our research group [1-11]. In search for new techniques to obtain films, we studied techniques like spray pyrolysis (SP), thermal evaporation (TE) and casting (CA). These low-cost techniques could be used to obtain films alternatively to high-cost techniques, which require sophisticated apparatus and are often more complicated to use. The properties of these materials are high atomic number (ZTl = 81, ZBr = 35, ZHg = , ZI = 53 and ZPb = 82), high mass density (dTlBr = 7.56 g/cm3, dHgI2 = 6.4 g/cm3 and dPbI2 = 6.2 g/cm3 ) and intrinsic band gap (2.68 eV for TlBr, 2.13 eV for HgI2 and 2.4 eV for PbI2). They are interesting for X- and Ȗ-rays detection [1-18]. In this work we fabricated films of these materials and characterized them using structural, morphological and electrical techniques. The main goal of this work is the comparison between these films. EXPERIMENTAL DETAILS Films of wide bandgap semiconductors were obtained using SP, TE and CA. The experimental apparatus of these techniques were described in previous works [1-11]. The fabrication conditions are discussed below: 1) TlBr films were obtained by SP and TE. For SP, Mili-Q water was used as solvent and the concentration of TlBr was 1mg/mL. The procedure and parameter of the technique were described previously [1]. Films produced by TE were based on 0.35g of the starting powder that
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sits on a tungsten crucible at a home-made TE apparatus [1-3]. We also studied the influence of the number of depositions on the final properties of the films; 2) HgI2 films were fabricated by SP and CA. Milli-Q water and Ethanol were used as solvent in SP and yellowish and reddish films were obtained respectively [4,5]. The concentration of HgI2 was 0.06 mg/mL in all studies. Experimental p
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