Lead Iodide Thin Films Grown using N.N-Dimethylformamide as Solvent
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0994-F03-05
Lead Iodide Thin Films Grown using N.N-Dimethylformamide as Solvent Jose Fernando Condeles, Ademar Marques Caldeira-Filho, and Marcelo Mulato Departamento de Física e Matemática, Universidade de São Paulo, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Av. Bandeirantes 3900, Ribeirão Preto-SP, CA, 14040-901, Brazil
Abstract Spray pyrolysis was used for the deposition of lead iodide (PbI2) thin films using N.Ndimethylformamide (DMF) as an alternative solvent under varying deposition parameters. Final thickness of 60 µm was obtained for a total deposition time of 2.5 hours. The films were characterized mainly by using Raman and photoluminescence, but additional techniques such as X-ray diffraction, scanning electron microscopy and dark conductivity as a function of temperature were also employed. Thick PbI2 films deposited by spray pyrolysis using DMF as a solvent are promising to be used in medical systems as X-ray imaging.
Introduction Lead iodide (PbI2) is a very promising wide band gap semiconductor material for applications in ionizing radiation detectors that operate at room temperature. Due to its properties the study of this material has been focused on the fabrication of X-ray detectors for digital radiography in medical systems [1]. PbI2 is an anisotropic semiconductor material with a hexagonal and lamellar structure made of a plane of lead atoms between two planes of iodine atoms (I-Pb-I). The bonding between the planes is weak (van der Waals). PbI2 does not present a destructive phase transition between room temperature and its melting point, as is the case for HgI2 [2]. Improvements in performance of bulk PbI2 detectors were reported [3], but the literature about the study on the thin film form is very limited. Note that this is the desired form for applications in large area devices in medical diagnosis. Thermally evaporated PbI2 presented high resolution and sensitivity both for static and dynamic imaging [1]. In this work the spray pyrolysis (SP) deposition method was used as an alternative technique for the deposition of PbI2 polycrystalline thin films with potential applications in X-ray detectors. This method is interesting because of its simplicity compared to other deposition methods. It can be easily expanded for large areas, it presents a reasonable deposition rate and it does not require expensive equipment [5]. The fabrication process using the deposition method and water as solvent together with the inclusion of extra iodine in the deposition atmosphere and comparing three starting powders was already discussed [6]. Water can be used to dissolve the PbI2 powder and employed in the technique as long as the substrate deposition temperature is greater than 100ºC. Nevertheless, one of the drawbacks of this solvent is the small final thickness of the films, i.e. only 3 µm for a total deposition time of 3 hours. In this work, the N.Ndymetilformamide (DMF) organic solvent was used for the dissolution of the PbI2, presenting a higher deposition rate.
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