Yazar "Turan, Rasit" seçeneğine göre listele

Listeleniyor 1 - 7 / 7
  • Küçük Resim Yok
    Öğe
    All Solution-Based Fabrication of Copper Oxide Thin Film/Cobalt-Doped Zinc Oxide Nanowire Heterojunctions
    (WILEY, 2016) Akgul, Funda Aksoy; Akgul, Guvenc; Turan, Rasit; Unalan, Husnu Emrah
    Versatile and intriguing solution-based processes are utilized to synthesize nanostructured materials for device applications to reduce material production and device fabrication costs. This study presents results on the fabrication and characterization of copper oxide ( CuO) coated cobalt-doped zinc oxide nanowires ( Co-doped ZnO NWs)-based heterojunction diodes prepared by a two-step synthesis route through combined hydrothermal growth and sol-gel spin coating. Highly dense, well-ordered, undoped, and Co-doped ZnO NWs were successfully grown by hydrothermal method. Complementary CuO thin films were synthesized by sol-gel method and subsequently coated onto both undoped and Co-doped ZnO NWs through spin-coating technique. Enhanced diode properties with a rectification ratio of 10(3) at +/-2 V and an ideality factor of n = 2.4 ( in dark) were obtained for Co-doped ZnO NWs-based heterojunction diodes. The obtained results demonstrated that the investigated heterojunction diode structure fabricated by facile and cost-effective solution-based processes can be a promising candidate for the next generation optoelectronic devices.
  • Küçük Resim Yok
    Öğe
    Enhanced diode performance in cadmium telluride-silicon nanowire heterostructures
    (ELSEVIER SCIENCE SA, 2015) Akgul, Funda Aksoy; Akgul, Guvenc; Gullu, Hasan Huseyin; Unalan, Husnu Emrah; Turan, Rasit
    We report on the structural and optoelectronic characteristics and photodetection properties of cadmium telluride (CdTe) thin film/silicon (Si) nanowire heterojunction diodes. A simple and cost-effective metal-assisted etching (MAE) method is applied to fabricate vertically oriented Si nanowires on n-type single crystalline Si wafer. Following the nanowire synthesis, CdTe thin films are directly deposited onto the Si nanowire arrays through RF magnetron sputtering. A comparative study of X-ray diffraction (XRD) and Raman spectroscopy shows the improved crystallinity of the CdTe thin films deposited onto the Si nanowires. The fabricated nanowire based heterojunction devices exhibit remarkable diode characteristics, enhanced optoelectronic properties and photosensitivity in comparison to the planar reference device. The electrical measurements revealed that the diodes have a well-defined rectifying behavior with a superior rectification ratio of 10(5) at +/- 5 V and a relatively small ideality factor of n = 1.9 with lower reverse leakage current and series resistance at room temperature in dark condition. Moreover, an open circuit voltage of 120 mV is also observed under illumination. Based on spectral photoresponsivity measurements, the nanowire based device exhibits a distinct responsivity (0.35-0.5 A W-1) and high detectivity (6 x 10(12)-9 x 10(12) cm Hz(1/2) W-1) in near-infrared wavelength region. The enhanced device performance and photosensitivity is believed to be due to three-dimensional nature of the interface between the CdTe thin film and the Si nanowires. The device characteristics observed here reveals that fabricated CdTe thin film/Si nanowire heterojunctions are promising for high-performance and low-cost optoelectronic device applications, near-infrared photodetectors in particular. (C) 2015 Elsevier B.V. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Fabrication and characterization of copper oxide-silicon nanowire heterojunction photodiodes
    (IOP PUBLISHING LTD, 2014) Akgul, Guvenc; Akgul, Funda Aksoy; Mulazimoglu, Emre; Unalan, Husnu Emrah; Turan, Rasit
    In this study, copper oxide (CuO) thin film/silicon (Si) nanowire heterojunctions have been fabricated and their optoelectronic performances have been investigated. Vertically aligned n-type Si nanowires have been fabricated using metal-assisted etching (MAE) technique. CuO thin films were synthesized by the sol-gel method and deposited onto the nanowires through spin-coating. Fabricated nanowire heterojunction devices exhibited excellent diode behaviour compared to the planar heterojunction control device. The rectification ratios were found to be 105 and 101 for nanowire and planar heterojunctions, respectively. The improved electrical properties and photosensitivity of the nanowire heterojunction diode was observed, which was related to the three-dimensional nature of the interface between the Si nanowires and the CuO film. Results obtained in this work reveal the potential of Si nanowire-based heterojunctions for various optoelectronic devices.
  • Küçük Resim Yok
    Öğe
    Improved diode properties in zinc telluride thin film-silicon nanowire heterojunctions
    (TAYLOR & FRANCIS LTD, 2015) Akgul, Funda Aksoy; Akgul, Guvenc; Gullu, Hasan Huseyin; Unalan, Husnu Emrah; Turan, Rasit
    In this study, structural and optoelectronic properties and photodedection characteristics of diodes constructed from p-zinc telluride (ZnTe) thin film/n-silicon (Si) nanowire heterojunctions are reported. Dense arrays of vertically aligned Si nanowires were successfully synthesized on (110)-oriented n-type single crystalline Si wafer using simple and inexpensive metal-assisted etching (MAE) process. Following the nanowire synthesis, p-type ZnTe thin films were deposited onto vertically oriented Si nanowires via radio frequency magnetron sputtering to form three-dimensional heterojunctions. A comparative study of the structural results obtained from X-ray diffraction and Raman spectroscopy measurements showed the improved crystallinity of the ZnTe thin films deposited onto the Si nanowire arrays. The fabricated nanowire-based heterojunction devices exhibited remarkable diode characteristics and enhanced optoelectronic properties and photosensitivity in comparison to the planar reference. The electrical measurements revealed that the diodes with nanowires had a well-defined rectifying behaviour with a rectification ratio of 10(4) at +/- 2V and a relatively small ideality factor of n=1.8 with lower reverse leakage current and series resistance at room temperature in dark condition. Moreover, an open-circuit voltage of 100mV was also observed under illumination. Based on spectral photoresponsivity measurements, the nanowire-based device exhibited a distinct responsivity and high detectivity in visible and near-infrared (NIR) wavelength regions. The device characteristics observed here offer that the fabricated ZnTe thin film/Si nanowire-based p-n heterojunction structures will find important applications in future and will be a promising candidate for high-performance and low-cost optoelectronic device applications, NIR photodedectors in particular.
  • Küçük Resim Yok
    Öğe
    Influence of thermal annealing on microstructural, morphological, optical properties and surface electronic structure of copper oxide thin films
    (ELSEVIER SCIENCE SA, 2014) Akgul, Funda Aksoy; Akgul, Guvenc; Yildirim, Nurcan; Unalan, Husnu Emrah; Turan, Rasit
    In this study, effect of the post-deposition thermal annealing on copper oxide thin films has been systemically investigated. The copper oxide thin films were chemically deposited on glass substrates by spin-coating. Samples were annealed in air at atmospheric pressure and at different temperatures ranging from 200 to 600 degrees C. The microstructural, morphological, optical properties and surface electronic structure of the thin films have been studied by diagnostic techniques such as X-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible (UV-VIS) absorption spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The thickness of the films was about 520 nm. Crystallinity and grain size was found to improve with annealing temperature. The optical bandgap of the samples was found to be in between 1.93 and 2.08 eV. Cupric oxide (Cuo), cuprous oxide (Cu2O) and copper hydroxide (Cu(OH)(2)) phases were observed on the surface of as-deposited and 600 degrees C annealed thin films and relative concentrations of these three phases were found to depend on annealing temperature. A complete characterization reported herein allowed us to better understand the surface properties of copper oxide thin films which could then be used as active layers in optoelectronic devices such as solar cells and photodetectors. (C) 2014 Elsevier B.V. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Integration of graphene with GZO as TCO layer and its impact on solar cell performance
    (Pergamon-Elsevier Science Ltd, 2022) Zan, Recep; Olgar, Mehmet Ali; Altuntepe, Ali; Seyhan, Ayse; Turan, Rasit
    In this study, we investigated the impact of incorporating graphene with Ga-doped ZnO (GZO) when employing them as a TCO layer on Si-based solar cell. GZO thin films with various thicknesses (50-450 nm) were fabricated by the sputtering method using a single target. The aim here was to determine the GZO film with the optimum thickness to incorporate it with single layer graphene as TCO. This thickness was found to be 350 nm as that was the best crystalline quality found in the Opattern. Further, this sample had the lowest sheet resistance and highest transmission values as confirmed by electrical (sheet resistance), and optical characterizations (transmission). Topographic (SEM and AFM), electrical (resistivity and carrier concentration) measurements were also conducted on the same sample. The graphene film grown on copper in a CVD system was then transferred on top of this sample to fabricate the hybrid TCO structure. We found that graphene integrated GZO hybrid TCO film showed higher sheet resistance due to high sheet resistance of graphene and similar optical properties thanks to high optical transmission of graphene. Employing graphene-based TCO layer in the solar cell resulted in higher open-circuit voltage, consequently improving the conversion efficiency from 10.0% to 11.2%. (c) 2021 Elsevier Ltd. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Photovoltaic performance of Gallium-doped ZnO thin film/Si nanowires heterojunction diodes
    (TAYLOR & FRANCIS LTD, 2016) Akgul, Guvenc; Akgul, Funda Aksoy; Unalan, Husnu Emrah; Turan, Rasit
    In this work, photovoltaic performance of Ga-doped ZnO thin film/Si NWs heterojunction diodes was investigated. Highly dense and vertically well-aligned Si NW arrays were successfully synthesised on a p-type (1 0 0)-oriented Si wafer through cost-effective metal-assisted chemical etching technique. Ga-doped ZnO thin films were deposited onto Si NWs via radio frequency magnetron sputtering to construct three-dimensional heterostructures. Photovoltaic characteristics of the fabricated diodes were determined with current density (J)-voltage (V) measurements under simulated solar irradiation of AM 1.5G. The optimal open-circuit voltage, short-circuit current density, fill factor and power conversion efficiency were found to be 0.37V, 3.30mAcm(-2), 39.00 and 0.62%, respectively. Moreover, photovoltaic diodes exhibited relatively high external quantum efficiency over the broadband wavelengths between 350 and 1100nm interval of the spectrum. The observed photovoltaic performance in this study clearly indicates that the investigated device structure composed of Ga-doped ZnO thin film/Si NWs heterojunctions could facilitate an alternative pathway for optoelectronic applications in future, and be a promising alternative candidate for high-performance low-cost new-generation photovoltaic diodes.