Preparation And Characterization Of Poly-Crystalline PbI₂ Films

Lead iodide (PbI₂) has been considered as a promising material for X-ray and y-ray room temperature detector, which is due to the high-atomic number of its elements (Z_Pb=82,Z_I=53) and wide band gap(E_g =2.3².6eV). There are many methods forpreparation PbI₂ thin film, but it is difficult to grow in large area and high quality using those techniques, so its application in large area nuclear image detector is limited. In this thesis, we first fabricated high-crystalline PbI₂ thin film with Chemical Bath Deposition. Note that an intrinsic advantage of vacuum evaporation is that it can be easily expanded for high purity, high compact and large areas in a low-cost manner, our work concentrate on both the theory and experiment about the vapor process. The main aspects of the thesis performed as follows:(1) The high-crystalline lead iodide films, were prepared with Chemical Bath Deposition.(2) The polycrystalline lead iodide films were fabricated on normal transparent glass and normal glass coated with aluminum electrode like a bar by evaporation growth in vacuum chamber. The structures, morphology, compositions and optical and electrical properties of the samples were analyzed by X-ray Diffraction Spectrum (XRD), Scan Electron Microscopy (SEM), Transmission Electron Microscope (TEM), Atomic Force Microscopy (AFM), X-ray Photoelectron Spectrum (XPS), high resistance instrument and Visible Ultraviolet Spectrum (VIS-UV). It was proved that the films were found to be nearly stoichiometry, the electrical resistance of lead iodide films achieved -10¹² Ω·cm;the activation energy of the dark conductivity is E_a = 0.78eV. The photo-conduction of lead iodide polycrystalline films were 366 timeslarger than the dark-conduction under the irradiating by 100mw/cm² white light, this result indicate the films have high photosensitive;The optical absorption was carried out in UV/VIS bands, and the calculated band-gap is between 2.550eV-2.590eV.(3) The response spectrum of y-ray in PbI₂ detector have been simulated, and compared with the test results.The present work is not only a solid base for further exploration on high quality PbI₂ film, but also an active endeavor in the application process as a room temperature nuclear detector and X-ray image detector.