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    Characterization of CdS films and CdS/Si heterojunctions prepared by ultrasonic spray pyrolysis and their response to light
    (Elsevier, 2020) Bilgin, Vildan; Sarica, Emrah; Demirselcuk, Barbaros; Erturk, Kadir
    In this work CdS thin films were deposited onto glass and p-Si substrates by ultrasonically spraying of precursor solutions prepared in molarity ranging from 0.025 M, to 0.1 M. Structural investigations revealed that all films have hexagonal structure and mean crystallite size was found to be in the range of 18 nm-21 nm. On the other hand, CdS films exhibited 65-70% optical transmittance and band gap energy for all films was found to be about 2.42 eV. Electrical measurements of CdS/Si heterojunctions were carried out under both dark and illumination conditions. Calculated ideality factor and zero-bias barrier height ranged from 3.02 to 2.66 and 0.74 eV-0.78 eV according to TE theory whereas they ranged from 6.91 to 4.73 and 0.71 eV-0.74 eV according to Cheungs' method. Increase in reverse saturation current when heterojunctions were illuminated indicated that they have good sensitivity to solar light.
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    Effect of Pb:S molar ratio in precursor solution on the properties of lead sulphide thin films by ultrasonic spray pyrolysis
    (Elsevier Sci Ltd, 2017) Sarica, Emrah; Bilgin, Vildan
    In this work, PbS thin films were deposited onto glass substrate at 225 degrees C by spraying precursor solution prepared with different molar ratio of lead acetate and thiourea as a source of Pb2+ and S2- respectively in order to investigate the effect of Pb:S molar ratio in the precursor solution on the physical properties of PbS thin films. Structural investigations carried out by X-ray diffractometer have shown that all films have fcc cubic structure and the average crystal size increased from 11 nm to 25 nm with the increasing the thiourea ratio in the precursor solution. In order to analyze the surface morphology of PbS thin films, AFM and SEM images were taken and elemental analysis of the films was performed by EDS. Optical transmittance and absorption spectra show that all deposited films have fairly low transmittance and high absorbance in the visible region. Additionally, it was determined that optical band gap of the deposited films were varied between 1.18 eV and 1.37 eV. As a consequence of electrical investigations, it was seen that all films have p-type conductivity and electrical resistivity decreased by increasing thiourea molar ratio in the precursor solution. All examinations have revealed that the molar ratio of lead acetate and thiourea has a significant effect on the physical properties of PbS thin films.
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    Iron doped ZnO thin films deposited by ultrasonic spray pyrolysis: structural, morphological, optical, electrical and magnetic investigations
    (Springer, 2018) Bilgin, Vildan; Sarica, Emrah; Demirselcuk, Barbaros; Turkyilmaz, Seren
    In this work, undoped and Fe-doped ZnO thin films at various concentrations (2, 4 and 6 at.%) were deposited onto glass substrate by using ultrasonic spray pyrolysis in order to investigate the effect of Fe doping on the structural, morphological, optical, electrical and magnetic properties of ZnO thin films. X-ray diffractometer (XRD) results revealed that all deposited thin films have hexagonal wurtzite structure and Fe doping led to decrease in mean crystallite size. Atomic force microscopy images showed that thin films were composed of tightly packed grains. Optical examinations indicated that optical transmittance remarkably decreased with the increase in the amount of Fe concentration in thin films. Additionally, optical band gap of deposited films were determined in the range of 3.26-3.29 eV. It was determined that all deposited thin films have n-type conductivity and electrical resistivity increased up to 253.6 Omega cm as a consequence of Fe doping. Vibrating sample magnetometer measurements showed that all films have ferromagnetic behavior.
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    Non-stoichiometric effect and disorder in as-prepared Cu2ZnSnS4 films deposited at different temperatures by ultrasonic spray pyrolysis
    (Elsevier Sci Ltd, 2022) Gunes, Ibrahim; Bilgin, Vildan; Sarica, Emrah
    A better understanding of its crystal structure, the formation of possible secondary phases, defects and Cu-Zn disorder effects is needed to improve the photovoltaic device performance of CZTS films. In this direction, the effect of deposition temperature on the structural inhomogeneities, such as secondary phases and Cu-Zn dis-order, etc. as well as opto-electrical properties of CZTS were experimentally examined. For this purpose, a non-stoichiometric spraying solution was prepared and ultrasonically sprayed onto glass substrates at different deposition temperatures (350 degrees C, 400 degrees C, 450 degrees C, and 500 degrees C) to obtain CZTS films. Afterward, the structural, morphological, elemental, optical, and electrical properties of the deposited films were investigated in detail. By Lorentzian deconvolution of Raman spectra, 14 Raman vibrational modes were detected and seven of these were assigned to the secondary phases. Also, the ordered-kesterite phase (337 cm-1) of CZTS was found to crystallize along with the disordered-kesterite phase (329 cm-1) due to the disorder of the cation (Cu-Zn) sublattice. Optical band gaps for CZTS films decreased from 1.89 eV to 1.42 eV with increasing in deposition temperature. It was seen that not only optical band gaps but also Cu-Zn disorder and the amount of secondary phases in CZTS films tightly depend on the deposition temperature.
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    Structural, optical, electrical and magnetic studies of ultrasonically sprayed ZnO thin films doped with vanadium
    (Elsevier Science Sa, 2016) Sarica, Emrah; Bilgin, Vildan
    Undoped and vanadium (V) doped (3, 6, 9 and 12 mol%) ZnO thin films were deposited onto glass substrates at the substrate temperature of 400 +/- 5 degrees C by ultrasonic spray pyrolysis technique. Depending on the doping concentration, the variation in the structural, morphological, elemental analysis, and optical, electrical and magnetic properties were investigated by means of X-ray diffractometer (XRD), atomic force microscope (AFM) and scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS), UV-vis spectrophotometer, current-voltage (I-V) measurements and vibrating sample magnetometer (VSM), respectively. The X-ray diffraction studies have revealed that all the films were polycrystalline with hexagonal wurtzite crystal structure. The transmittance in the visible region varied between 55 and 75% and it was observed that transmittance of deposited films decreased after incorporation of vanadium. The electrical resistivity studies for all the films were carried out by using the two-probe method and it was seen that the electrical resistivity of the ZnO films decreased sharply as a consequence of V doping. The VSM measurements showed that all deposited films have intrinsic ferromagnetic behavior at room temperature and it was also found that the ferromagnetic behavior of all the films was obviously affected by doping with vanadium. (C) 2015 Elsevier B.V. All rights reserved.
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    Study of some physical properties of ultrasonically spray deposited silver doped lead sulphide thin films
    (Elsevier Sci Ltd, 2017) Sarica, Emrah; Bilgin, Vildan
    In this study, undoped and Ag doped PbS thin films at different concentrations were deposited onto glass substrates at 225 degrees C by using ultrasonic spray pyrolysis technique, in order to investigate the effect of Ag doping on the physical properties of PbS thin films. Structural investigations revealed that all doped PbS: Ag thin films have cubic structure and Ag doping enhances crystalline level of PbS thin films. It was determined that average crystallite size of PbS: Ag thin films increased from 24 nm to 49 nm by increasing Ag doping concentration. Morphological studies showed that surfaces of the films become denser after Ag doping. Optical transmittance and absorption spectra revealed that all deposited thin films have low transmission and high absorbance within the visible region and band gap energy of the PbS:Ag thin films were determined to be in the range of 1.37 eV and 1.28 eV by means of optical method. Electrical conductivity type of PbS: Ag films was determined to be p-type and calculated electrical resistivity was found to be lowest for Ag-doped PbS thin films at 2%.