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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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    Improvement in performance of SnSe-based photodetectors via post deposition sulfur diffusion
    (Elsevier Science Sa, 2024) Yilmaz, Salih; Basol, Bulent M.; Polat, Ismail; Olgar, Mehmet Ali; Bayazit, Tugba; Kucukomeroglu, Tayfur; Bacaksiz, Emin
    The work represents an enhancement in the photodetector properties of thermally evaporated SnSe thin films through both annealing and sulfurization processes. X-ray diffraction analysis showed the formation of SnSe 1-x S x alloy with a graded composition that was more S -rich near the surface when the sulfurization process was applied at 350 degrees C. Scanning electron microscopy results indicated that increasing the annealing temperature from 300 degrees C to 350 degrees C changed the microstructure greatly. When the sulfurization temperature was increased from 300 degrees C to 350 degrees C, the direct band gap of SnSe thin films decreased from 1.38 eV to 1.30 eV while the indirect band gap reduced from 0.91 eV to 0.71 eV. Raman spectra also confirmed the development of phase of SnSe 1-x S x for the sulfurized sample at 350 degrees C. Photocurrent-time curves of devices fabricated on all films demonstrated that sulfurization at high temperature increased the photocurrent values. It was further determined that devices made on sulfurized layers had smaller rise/fall times of 2.57/2.33 s compared to those fabricated on non-sulfurized films. The best responsivity and detectivity values were achieved as 2.07 x 10 -1 A/W and 1.19 x 10 7 Jones, respectively, for photodetectors fabricated on layers sulfurized at 350 degrees C.