الفهرس 
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Abstract
PbS thin films were deposited on glass substrates using the simplest and low cost chemical bath deposition technique (CBD). Three different lead sources namely lead nitrate, lead acetate and lead chloride have been used for the synthesis with thiourea as sulphur source and sodium hydroxide as a base medium. The effect of change lead sources on structural, surface morphological optical and electrical properties was discussed. According to X-ray diffraction studies, all the films were polycrystalline with face centered cubic structure. The average crystallite sizes were found to be in the range 40-64 nm, Thus, XRD studies reveal that the films deposited by CBD were formed from monocrystalline PbS. AFM images show different morphology for films, The crystalline grains were relatively good, grain sizes were uniformly distributed on the surface of the substrate for film prepared using lead nitrate as a lead source, whereas for samples prepared using lead acetate and lead chloride as a lead sources grain sizes were non uniformly distributed on the surface of the substrate The SEM photographs showed diverse morphology. The optical band gap is found to be very sensitive to the metal sources used. The direct band gap energy values obtained are in the range of 1.50–1.77 eV. The Samples prepared using nitrate as metal source from the properties are found to be the best metal source for preparing PbS thin films. For higher thickness the reaction was repeated and the thickness was doubled. The reaction was repeated three times and get four different thicknesses 300,600,900 and 1200nm. The effect of varying the film thickness on the structural and optical properties has been investigated. Increasing the film thickness enhances the crystallinity of the films as well as decreases the strain and dislocation density. The surface morphology features were studied using Scanning electron microscopy and it dramatically changed from small spherical grains to bead-like shape. The absence of impurities in the deposited films was confirmed by energy dispersive x-ray spectrometry (EDX) measurements, the atomic or weight concentration of each element varies with changing the film thickness which can be attributed to the rate of chemical reaction. The energy gap decreases with increasing the film thickness. This is related to the increment in the crystallite size with increasing the film thickness. The reported band gap energy of bulk PbS ranges from 0.4 to 0.6 eV. The obtained higher values can be attributed to the quantum confinement effect. The optical constants of the deposited films were calculated. Films were sensitized with thermal heat and 808nm CW laser, Effect of laser beam on structure, optical, electrical properties of PbS thin films were examined at different laser powers 1W, 2W, 3W, 4Wand 5Wthe samples irradiated for 3min. PbS samples were tested as photoconductive detector. The PbS samples signals were compared with the commercial detector signal. The sample detector responsivity increased with sensitization by heating as well as the responsivity of sample detector increase by increasing laser power and sample thickness.