Yazar "Polat, Ismail" seçeneğine göre listele

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    Enhancement of the response speed of CIGS-based photodetector by Te-doping
    (Elsevier Science Sa, 2024) Yilmaz, Salih; Basol, Bulent M.; Atasoy, Yavuz; Polat, Ismail; Kucukomeroglu, Tayfur; Bacaksiz, Emin
    Cu(In,Ga)Se2 (CIGS) based devices are promising candidates for high performance photodetector applications. The present work investigated the effects of Te-doping on the properties of CIGS layers and studied the performance of photodetectors (PDs) fabricated on these films. The films were vacuum evaporated on glass substrates and their morphological, structural and optical properties were evaluated after an annealing step at 550 degrees C. Morphological data indicated that undoped CIGS films had non-uniform surface features with large grains separated by nanoparticles. Addition of 6.6 % Te improved the morphology and yielded a smoother layer. Further increase in Te concentration showed appreciable reduction in surface feature size and shape. X-ray diffraction patterns showed that increasing the Te amount in CIGS caused a shift in the XRD peaks towards smaller angles pointing to replacement of Se atoms by Te. Peak splitting at higher Te samples suggested a graded structure with Se and Te amounts changing through the thickness of the film. Raman analysis demonstrated formation of CuInGa(Se,Te)2 (CIGST) compound. According to Tauc's approximation, CIGS films with and without Te atoms possessed two energy band gaps of Eg1 and Eg2 that were in the ranges of 1.10-1.28 eV and 1.16-1.36 eV, respectively. Electrical data obtained from photodetector devices showed a responsivity of 4.44x10- 1 A/W and a detectivity of 8.01x107 Jones for Te-free material, while the rise/fall times were measured as 34/148 ms. A much faster response speed of 19/20 ms was reached for devices fabricated on films with 10.2 % Te. This work demonstrated, for the first time, the fabrication low-cost and high-performance metalsemiconductor-metal (MSM) type CIGST-based PDs.
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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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    Investigation of growth temperature effects on SnSe-based photodetector performance
    (Springer, 2023) Yilmaz, Salih; Basol, Bulent M.; Polat, Ismail; Ciris, Ali; Kucukomeroglu, Tayfur; Bacaksiz, Emin
    SnSe thin films were synthesized by thermal evaporation on glass slides at elevated growth temperatures. The grown films were investigated in terms of structural, morphological and optical properties. Furthermore, electrical characteristics and time-dependent photoresponses of SnSe-based photodetectors were studied in depth. SnSe thin films showed orthorhombic crystal structure with a preferred orientation of (400) for the growth temperature of 150 & DEG;C. However, the preferential orientation changed from (400) to (111) with increasing of growth temperature to 200 & DEG;C. Top view SEM data displayed a porous morphology for the samples grown at 200 & DEG;C and 250 & DEG;C temperatures. More transparent SnSe films were obtained when the growth temperature was increased to 200 & DEG;C. The band gaps of SnSe sample deposited at 150 & DEG;C and 200 & DEG;C were determined to be 1.22 eV. However, band gap reduces to 1.06 eV with the increase of the substrate temperature to 250 & DEG;C. Raman data demonstrated the shift in the general peak positions to higher frequencies as the growth temperature is increased due to the variation in bond lengths between Sn and Se atoms. Photocurrent-time data showed that SnSe sample grown at a growth temperature of 200 & DEG;C possessed the highest photocurrents because of the formation of porous structure. Rise and fall times of SnSe-based photodetector decay systematically with increasing growth temperature and the maximum responsivity and detectivity were found to be 3.33 x 10-1 A/W and 2.03 x 107 Jones, respectively for the device employing the film deposited at 200 & DEG;C.
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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.