Yazar "Olgar, M. Ali" seçeneğine göre listele

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    Characterization of Cu(In,Ga)(Te,S)2 thin films grown on stainless steel foil substrates
    (Iop Publishing Ltd, 2023) Karaca, Abdullah; Basol, Bulent M.; Olgar, M. Ali; Buyuklimanli, Temel; Tomakin, Murat; Kucukomeroglu, Tayfur; Bacaksiz, Emin
    In this study, Cu(In,Ga)(Te,S)(2) (CIGTS) thin films with [Ga]/([In] +/- [Ga]) atomic ratios in the ranges of 0.22-0.28 and 0.50-0.67 were fabricated using a two-stage technique. During the first stage of the technique, in one set of samples, Cu, In and Ga layers were deposited by electrodeposition on a Mo coated stainless steel (SS) foil substrate forming a SS/Mo/Cu/In/Ga precursor structure. For another set of samples, a Te layer was also deposited by e-beam evaporation on the SS/Mo/Cu/In/Ga structure forming a SS/Mo/Cu/In/Ga/Te precursor structure. During the second stage, SS/Mo/Cu/In/Ga and SS/Mo/Cu/In/Ga/Te stacks were reacted using rapid thermal annealing (RTA) for 5 min at 600 degrees C with or without presence of S vapors to produce CIGTS series thin films. SS/Mo/Cu/In/Ga stack under S atmosphere yielded CuInGaS2 with a Ga-In gradient across the thickness by RTA process. SS/Mo/Cu/In/Ga/Te stack reacted without S in the reaction atmosphere yielded the CuInGaTe2 compound. When S was present, the same stack with top Te layer yielded only CuInGaS2 compound. When, however, already formed CuInGaTe2 compound layers were heated in S environment at 400 degrees C, some Te could be retained in the films in the form of elemental Te. Gallium and In grading in various reacted films were evaluated by x-ray diffraction, secondary-ion mass spectrometry and EDS. CIGTS films showed highly (112) preferred oriented chalcopyrite phase and with the increase of Ga content, shifts were observed in the XRD peak positions demonstrating Ga inclusion in the lattice. Gibbs free energy calculations were used to explain the preferred reaction of S with metallic constituents when both S and Te were present for reaction.
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    Growth and characterization of CT(S,Se) thin films and Al/n-Si/p-CT(S,Se)/Mo heterojunction diode application employing a two-stage process
    (Elsevier Science Sa, 2023) Bayazit, Tugba; Olgar, M. Ali; Kucukomroglu, Tayfur; Bacaksiz, Emin; Tomakin, Murat
    Cu2SnS3 (CTS), Cu2Sn(S,Se)(3) (CTSSe), and Cu2SnSe3 (CTSe) thin films were deposited on n-type silicon wafer substrates using a two-stage process. This process involved drop-coating Cu-Sn precursors, which is different from the vacuum-based fabrication methods. The sulfurization/selenization of the films was achieved using the rapid thermal processing (RTP) method at 550 degrees C. The structural, morphological, and optical properties of CTS, CTSSe, and CTSe thin films were investigated. Al/n-Si/p-CTS/Mo, Al/n-Si/p-CTSSe/Mo, and Al/n-Si/p-CTSe/Mo heterojunction diodes were formed, and electrical characterizations were performed. According to the performed analyses, it was detected that while CTS and CTSSe thin films had a Cu-poor chemical composition (Cu/Sn similar to 1.7), the CTSe thin film showed a Cu-rich chemical composition. X-ray diffraction (XRD) and Raman spectra of the samples showed that all samples had a monoclinic crystal structure as a dominant phase. Scanning electron microscope (SEM) images showed that the incorporation of selenium (Se) into prepared samples contributes to form a larger-grained structure. The band gap (E-g) of CTS, CTSSe, and CTSe thin films was determined from the optical reflectance measurements, and they were found to be 1.02 eV, 1.00 eV, and 0.96 eV, respectively. According to the data obtained from the I-V measurements of the heterojunction diode, the incorporation of Se into the film structure reduced the series resistance (R-s) in the heterojunctions from 8.27 x 10(2) Omega to 2.42 x 10(2) Omega, and the best ideality factor value was obtained in the Al/n-Si/p-CTSe/Mo heterojunction with a n = 2.87 value.
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    Photodetector properties of CdSe thin films grown by close space sublimation method
    (Springer, 2023) Olgar, M. Ali; Basol, Bulent M.; Polat, Ismail; Tomakin, Murat; Kucukomeroglu, Tayfur; Bacaksiz, Emin
    In the present study, CdSe thin films were grown by Close Space Sublimation (CSS) method on glass substrates at elevated temperatures. The prepared films were analyzed through several characterization techniques such as XRD, SEM, EDX, optical transmission, and photoluminescence. Films had single phase hexagonal crystal structure without any obvious secondary phase segregation. The preferred orientation was (002). SEM images taken from the surface and cross-section of the layers showed well-defined faceted microstructure with a grain size ranging from 0.5 to 1.0 & mu;m. The chemical composition was stoichiometric. Optical band gap calculated from the optical transmission was determined to be 1.73 eV. Room temperature PL spectra showed a single strong peak located at around 715 nm that can be attributed to free carrier-to-band or band-to-band optical transitions. The performance of photodetector devices constructed using the CSS grown CdSe films showed a wavelength dependent behavior, shorter wavelength light generating higher photocurrent. It was seen also determined that the responsiveness and detectivity values increased with decreasing value of the light wavelength. Switching properties, responsivity and detectivity of the photodetectors were studied. The maximum responsivity was observed at 714 nm. Devices yielded the highest photocurrent at a wavelength of 443 nm.