Yazar "Olgar, Mehmet Ali" seçeneğine göre listele

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    Exploring the relationship between reaction temperature and photodetection properties in Sb2Se3 thin film-based devices
    (Elsevier, 2025) Olgar, Mehmet Ali; Yilmaz, Salih; Rehman, Fazal; Bacaksiz, Emin
    This paper focuses on optimizing the reaction temperature of Sb2Se3 thin films for photodetector applications. The films were grown using a two-stage method on glass substrates. Structural analysis revealed the formation of the orthorhombic Sb2Se3 phase along the (020) plane, and increasing the reaction temperature up to 400 degrees C improved the crystal quality. Notably, the most promising structural properties were achieved for Sb2Se3 thin films reacted at 380 degrees C. Raman spectra confirmed the presence of tetragonal and amorphous selenium, along with Sb2Se3. Morphological analysis showed that a horizontally aligned rod morphology developed as the Sb2Se3 thin film grew, with the rod sizes increasing as the reaction temperature reached to 400 degrees C. X-ray photoelectron spectroscopy (XPS) revealed the formation of Sb-Se and Sb-O bonds, along with the presence of unreacted oxygen atoms near the surface of Sb2Se3 thin films reacted at 340 degrees C. Photoluminescence data indicated a bandgap value of 1.24 eV for Sb2Se3 films reacted at 380 degrees C. The current-voltage (I-V) curves exhibited a linear dependence for all Sb2Se3-based devices, suggesting ohmic contact between the films and the electrodes. The fastest photo- response was observed for the photodetector annealed at 380 degrees C, with rise and fall times of 26 ms and 40 ms, respectively. Additionally, the highest responsivity (R = 8.0 x 10-4 A/W), detectivity (D* = 3.8 x 106 Jones), and external quantum efficiency (EQE = 16.3%) were achieved by the same device, indicating that the optimal reaction temperature for Sb2Se3 thin films and their photodetector applications is approximately at 380 degrees C.
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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.
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    Understanding the role of sulfurization temperature and sulfur amount in two-stage fabricated Sb2S3 thin films for photodetection
    (Elsevier, 2026) Olgar, Mehmet Ali; Keser, Yasemen Ince; Cam, Meryem; Daday, Mine Taykurt; Yilmaz, Salih; Bacaksiz, Emin; Zan, Recep
    Sb2S3 thin films were fabricated via a two-stage process for photodetector applications. In the first stage, Sb thin films deposited by sputtering were sulfurized at various temperatures (350-425 degrees C) using a fixed sulfur amount (10 mg), and in the second, the sulfur amount (10-25 mg) was varied at 375 degrees C. The effects of sulfurization conditions on the chemical composition, crystal structure, surface morphology, optical, and electrical properties were systematically studied. This study establishes the critical role of sulfurization temperature and sulfur amount in determining the structural evolution and stoichiometry of Sb2S3 thin films, thereby enabling control over their photo-sensing performance. The optimal S/Sb ratio (approximate to 1.07-1.08) and crystallinity were achieved at 375 degrees C, yielding the large-grained, lower defect-free films with preferential (hk1) orientation. Increasing the sulfur amount enhanced the S/Sb ratio up to 1.43 but introduced an undesired (hk0) orientation beyond 20 mg. The sample prepared with 15 mg sulfur (SbS-375-15) exhibited favorable morphology, a proper bandgap (1.68 eV), the highest carrier concentration, and lowest resistivity, making it the best photodetector candidate. The corresponding device showed low dark current (<1 nA), high photocurrent (similar to 10 nA), fast response (rise/fall: 11.2/12.7 ms), sensitivity of 1090 %, detectivity of 2.45 x 10(6) Jones, and an external quantum efficiency (EQE) of 0.841 %, demonstrating the strong potential of Sb2S3 for high-performance photodetectors.
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    Unveiling improvements in structural, optical, and photodetection characteristics of CZTS thin films through Ag-doping
    (Elsevier, 2025) Rehman, Fazal; Yilmaz, Salih; Polat, Ismail; Bacaksiz, Emin; Zan, Recep; Olgar, Mehmet Ali
    The study investigated the characterization of photodetectors made from CZTS (Cu2ZnSnS4) thin films by introducing silver (Ag) as a dopant. CZTS thin films were grown on Mo-foil by two stage process, comprising sputter deposition of metallic precursor layers followed by sulfurization process employing Rapid Thermal Annealing (RTA) approach. The stacking order for the undoped and Ag-doped CZTS thin films were Substrate/ ZnS/Cu/Sn/Cu and Substrate/ZnS/Cu/Sn/Cu/Ag, respectively. Photodetectors (PDs) were fabricated using sputter deposition on glass, including CZTS, Ag-doped CZTS-5 (8 nm Ag), Ag-doped CZTS-10 (16 nm Ag), and Agdoped CZTS-15 (24 nm Ag). Various characterization methods were utilized to examine the prepared thin films, including Energy Dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), optical transmission, Photoluminescence (PL) and photodetection analyses. Among all devices, Ag-CZTS-10 PDs exhibited the best performance, showing a crystallite size (D) of 51.72 nm, band gap of 1.47 eV and favorable SEM surface morphology. For the photodetection characteristics, blue light at 443 nm and red light at 525 nm wavelength were used with an applied bias of 2V, and a light intensity of 17.3 mW/cm2. The highest responsivity (R) values recorded for Ag-CZTS-10-based PDs were 0.0024 A/W for blue and 0.0019 A/ W for red light. Additionally, the detectivity (D*) was 3.4 x 106 Jones for blue and 2.3 x 106 Jones for red light, while sensitivity (S) was 26 % for blue and 15 % for red light. This study successfully demonstrated, for the first time, the fabrication of low-cost, high-performance Ag-doped CZTS films-based PDs on glass substrates which hold promise for the development of cost-effective and efficient optoelectronic devices.