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    Crystalline structure and morphological properties of undoped and Sn doped ZnO thin films
    (Academic Press Ltd- Elsevier Science Ltd, 2009) Caglar, Yasemin; Aksoy, Seval; Ilican, Saliha; Caglar, Mujdat
    Undoped and tin (Sn) doped ZnO thin films have been prepared by spray pyrolysis method. Effect of Sri dopant on the crystalline structure and morphological properties of ZnO thin films has been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) method. XRD patterns confirm that the films have polycrystalline nature. While undoped ZnO film has (101) as the preferred orientation, Sri doped ZnO thin films have (002) as the preferred orientation. Grain sizes, lattice parameters and texture coefficient values of the films were determined. Microstructure was analyzed by SEM and the influence of the doping concentration in the microstructure of the films is investigated. (C) 2009 Elsevier Ltd. All rights reserved.
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    Effect of loading and standbye time of the organic dye N719 on the photovoltaic performance of ZnO based DSSC
    (Elsevier Science Bv, 2019) Aksoy, Seval; Gorgun, Kamuran; Caglar, Yasemin; Caglar, Mujdat
    In this work, ZnO nanopowders were synthesized by microwave assisted hydrothermal method. To measure the photoelectrochemical properties of the obtained ZnO nanopowders, ZnO film was coated on FTO by using doctor blade method and the dye solution consisting N719 was used. For the investigations of structural and morphological properties, X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) analysis were carried out. The optical reflectance of the ZnO films with and without dye were recorded using spectrophotometer and by using Kubelka-Munk function, the two optical band gaps were detected at about 3.25 eV (direct band gap of ZnO) and 2.20 eV. The current-voltage (I-V) characterizations of fabricated ZnO-DSSCs were performed for three consecutive days and the best performance was obtained from the cell at 2 h loading time and 2 day standbye time, with their photovoltaic parameters were the J(sc) of 1.62 mAcm(-2), V-oc of 0.64 V, FF of 0.62, and n% of 0.64%, respectively. (C) 2019 Elsevier B.V. All rights reserved.
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    Fabrication of p-Si/n-ZnO:Al heterojunction diode and determination of electrical parameters
    (Elsevier Science Bv, 2018) Ilican, Saliha; Gorgun, Kamuran; Aksoy, Seval; Caglar, Yasemin; Caglar, Mujdat
    We present a fundamental experimental study of a microwave assisted chemical bath deposition (MW-CBD) method for Al doped ZnO films. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) spectroscopy were used to analyze the microstructures and crystalline structures of these films, respectively. The p-Si/n-ZnO:Al heterojunction diodes were fabricated. The current-voltage (I-V) characteristics of these diodes were measured at room temperature. The important electrical parameters such as series resistance, the ideality factor and the barrier height were determined by performing plots from the forward bias I-V characteristics using different methods. The obtained results indicate that Al doping improve the electrical properties of the p-Si/n-ZnO diode. The best rectification properties were observed in the p-Si/n-ZnO:5%Al heterojunction diode, so only capacitance-voltage (C-V) measurements of this diode were taken. Electrical parameter values such as series resistance, the built-in potential and the acceptor concentration calculated for this heterojunction diode. (C) 2017 Elsevier B.V. All rights reserved.
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    Li doped ZnO based DSSC: Characterization and preparation of nanopowders and electrical performance of its DSSC
    (Elsevier, 2020) Aksoy, Seval; Polat, Ozgur; Gorgun, Kamuran; Caglar, Yasemin; Caglar, Mujdat
    In this study, microwave-assisted hydrothermal method (MW-HT) has been used to synthesize the nanopowders of Li doped ZnO, which are used in fabrication of dye-sensitized solar cell (DSSC). XRD examinations have shown that Li doped ZnO nanopowders synthesized in different concentration have highly crystallized hexagonal structure. To investigate the morphology of nanopowders, scanning electron microscopy (SEM) has been used and the results have revealed the nanoflower morphology of Li doped ZnO powders. Kubelka-Munk function has been utilized to determine the band gap of bare and dye loaded Li doped ZnO samples and an increase from 3.21 eV to 3.24 eV has been observed in the band gap as increasing Li content. The results of solar cell performance of the fabricated Li doped ZnO based DSSC samples have been exhibited that the efficiency of cells increases as the Li doping ratio is boosted and it has been observed the highest efficiency value of 1.23% for LZ10-DSSC.
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    THE CURRENT-VOLTAGE CHARACTERISTICS OVER THE MEASUREMENT TEMPERATURE OF 60-400 K IN THE Au/Ti/n-GaAs CONTACTS WITH HIGH DIELECTRIC HfO2 INTERFACIAL LAYER
    (World Scientific Publ Co Pte Ltd, 2019) Karabulut, Abdulkerim; Orak, Ikram; Caglar, Mujdat; Turut, Abdulmecit
    The Au/Ti/HfO2/n-GaAs metal/insulating layer/semiconductor structures have been fabricated using standard thermal atomic layer deposition. We experimentally showed whether or not the HfO2 interfacial layer grown on the n-GaAs wafer modifies the barrier height (BH) of the device at the room temperature. Besides, we investigated the measurement based on temperature dependence of the device parameters from the current-voltage (I-V) characteristics of the diode in 60-400 K range with steps of 10 K. The X-ray photoelectron spectroscopy (XPS) have been carried out to characterize the surfaces of both n-GaAs wafer and HfO2 thin films. The series resistance value from the temperature-dependent I-V characteristics decreased with decreasing temperature, which is a desired positive result for the devices developed from the MOS capacitor. The BH value of 0.94 eV (300 K) has been obtained for the device with the HfO2 layer which is a higher value than the value of 0.77 eV (300 K) of the device without HfO2 layer. Therefore, we can say that the HfO2 thin layer at the metal/GaAs interface can also be used for the BH modification as a gate insulator for GaAs MOS capacitor and MOSFETs. When the temperature-dependent I-V characteristics at low temperatures have been considered, it has been observed that the current prefers to flow through the lowest BHs due to the BH inhomogeneities.