Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 4Citation - Scopus: 5Enhanced Optoelectronic Properties of Magnetron Sputtered Ito/Ag Multilayers by Electro-Annealing(AVS, 2022) Uyanık, Zemzem; Türkoğlu, Fulya; Köseoğlu, Hasan; Ekmekçioğlu, Merve; Ata, Bengü; Demirhan, Yasemin; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, LütfiIndium tin oxide/silver/indium tin oxide (ITO/Ag/ITO) multilayers have attracted much attention to fulfill the growing need for high-performance transparent conducting oxide electrodes. To make these transparent multilayers work better, electro-annealing, which is a method of self-heating by electric current, can be effective. Moreover, the effect of current on ITO/Ag/ITO multilayers should be investigated to make sure that electronic devices will be reliable over their lifetime. In this study, ITO/Ag/ITO multilayer electrodes with varying Ag thicknesses were grown by DC magnetron sputtering at room temperature. Structural, optical, and electrical properties of these multilayers were investigated before and after electro-annealing. Measurement results revealed that improved optical transmittance and sheet resistance can be obtained by the optimization of Ag thickness for the as-grown ITO/Ag/ITO layers. The highest figure of merit (FoM) value of 17.37 × 10−3 Ω−1 with optical transmittance of 85.15% in the visible region and sheet resistance of 11.54 Ω/□ was obtained for the Ag thickness of 16.5 nm for as-grown samples. The electro-annealing of as-grown ITO/Ag/ITO multilayers led to improved optical behavior of the multilayer structure over a wide spectral range, especially in the near-infrared range. Electro-annealing also provided an improvement in the crystallinity and sheet resistance of the electrodes. The improvement of the electrical and optical properties of the structure enabled a FoM of 23.07 × 10−3 Ω−1 with the optical transmittance of 86.80% in the visible region and sheet resistance of 10.52 Ω/□. The findings of this work provide proper knowledge of the properties of ITO/Ag/ITO multilayers under electrical current and suggest that the overall performance of the multilayers can be improved by the electro-annealing process.Conference Object Reactive Ion Beam Etching of Superconducting Bi2212 by Ta/Pr and Pr'/ta/pr Masks for the Generation of Thz Waves(Institute of Electrical and Electronics Engineers Inc., 2009) Köseoğlu, Hasan; Türkoğlu, Fulya; Demirhan, Yasemin; Meriç Polster, Zeynep; Özyüzer, LütfiGeneration of powerful THz radiation from intrinsic Josephson Junctions (Ills) of Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) may require mesas with large lateral dimension. However, there are difficulties in fabrication of perfect rectangular mesas. Mesa lateral angles should be close to 90 degrees to obtain IJJs with same planar dimensions for synchronization of IJJs. Since thick photoresist (PR) layer shades the lateral dimension of mesa during ion beam etching, we patterned Ta/PR and PR'/Ta/PR masks on Bi2212 and used selective ion etching to overcome this problem. The reactive ion beam etchings have done with ion beam of Ar, N(2) and O(2) and we have obtained mesas about 1 mu m with lateral angle of approximately 50 to 75 degrees which is better than the mesas fabricated with single layer mask.Article Citation - WoS: 31Citation - Scopus: 33The Controllable Deposition of Large Area Roll-To Sputtered Ito Thin Films for Photovoltaic Applications(Elsevier, 2020) Demirhan, Yasemin; Köseoğlu, Hasan; Türkoğlu, Fulya; Uyanık, Zemzem; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, LütfiIn the present study, using a large area roll-to-roll DC magnetron sputtering system deposition of ITO thin films on polyethylene terephthalate (PET) substrates were achieved. In order to investigate the effect of growth conditions on the film properties all through the deposition process, optical emission spectroscopy (OES) analysis have been accomplished in a governable way. The consequences of Oxygen partial pressure and film thickness on electrical, and optical properties of the films were determined. It was shown that the intensity of optical emission peaks are subjected to the discharge power and as well as the O-2/Ar flow ratio. Large area, uniform ITO films with relatively high transparency and low electrical resistivity (R(2)(<)50 Omega/sqr) were succesfully deposited on PET substrates. The significance of both the figure of merit (FOM) and the optical band gap values on the performance of different TCO thin films were addressed. In this work, the obtained results suggest that the overall performance is sufficient to implement the ITO films in photovoltaic and OLED applications. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 21Citation - Scopus: 24Effect of Defects and Secondary Phases in Cu2znsns4 Absorber Material on the Performance of Zn(o,s) Buffered Devices(Elsevier Ltd., 2019) Türkoğlu, Fulya; Köseoğlu, Hasan; Cantaş, Ayten; Akça, Fatime Gülşah; Meriç, Ece; Buldu, Dilara Gökçen; Aygün, GülnurCopper zinc fin sulfide (CZTS) absorber layer attracts so much attention in photovoltaic industry since it contains earth abundant, low cost and non-toxic elements contrary to other chalcogenide based solar cells. In the present work, CZTS absorber layers were prepared following a two-stage process: firstly, a stack of metal precursors (Copper (Cu)/Tin (Sn)/Zinc (Zn)/Copper (Cu)) were deposited on molybdenum (Mo) substrate by magnetron sputtering, then this stack was annealed under S atmosphere inside a tubular furnace. CZTS thin films were investigated using energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The effect of sulfurization time and the thickness of top and bottom Cu layer in precursors on the properties of CZTS thin films were investigated. The importance of Cu thickness adjacent to Sn to avoid detrimental phases was addressed. The significance of sulfurization time to restrict the Sn and Zn losses, formation of oxides such as fin dioxide and zinc oxide, and formation of molybdenum disulfide and voids between Mo/CZTS interface was also addressed. Moreover, cadmium sulfide buffer layer, which is conventionally used in CZTS solar cells, is replaced by an environmentally friendly alternative zinc oxysulfide buffer layer.Article Citation - WoS: 15Citation - Scopus: 17Effect of Substrate Rotation Speed and Off-Center Deposition on the Structural, Optical, and Electrical Properties of Azo Thin Films Fabricated by Dc Magnetron Sputtering(American Institute of Physics, 2018) Türkoğlu, Fulya; Aygün, Gülnur; Köseoğlu, Hasan; Özdemir, Mehtap; Zeybek, S.; Özyüzer, Lütfi; Özdemir, Mehtap; Özyüzer, Gülnur Aygün; Özyüzer, LütfiIn this study, aluminum-doped zinc oxide (AZO) thin films were deposited by DC magnetron sputtering at room temperature. The distance between the substrate and target axis, and substrate rotation speed were varied to get high quality AZO thin films. The influences of these deposition parameters on the structural, optical, and electrical properties of the fabricated films were investigated by X-ray diffraction (XRD), Raman spectroscopy, spectrophotometry, and four-point probe techniques. The overall analysis revealed that both sample position and substrate rotation speed are effective in changing the optical, structural, and electrical properties of the AZO thin films. We further observed that stress in the films can be significantly reduced by off-center deposition and rotating the sample holder during the deposition. An average transmittance above 85% in the visible range and a resistivity of 2.02 × 10-3Ω cm were obtained for the AZO films.Article Citation - WoS: 60Citation - Scopus: 64Improvement of Optical and Electrical Properties of Ito Thin Films by Electro-Annealing(Elsevier Ltd., 2015) Köseoğlu, Hasan; Türkoğlu, Fulya; Kurt, Metin; Yaman, Mutlu Devran; Akça, Fatime Gülşah; Aygün, Gülnur; Özyüzer, LütfiThe effect of electro-annealing in vacuum and air on the optical and electrical properties of ITO thin films grown by large area DC magnetron sputtering was investigated. Moreover, the performances of the electro-annealed ITO thin films in vacuum and air were compared. Electro-annealing was performed by applying 0.75, 1.00, 1.25 and 1.50 A constant ac current to the ITO thin films. It was observed that the crystallinity of the films was better for the ITO thin films electro-annealed in vacuum. The changes in sheet resistance of electro-annealed ITO thin films with applied currents were detailed. The transmittance of the films increased for both electro-annealing in vacuum and air. A correlation between band-gap and resistivity for all of the electro-annealed thin films was observed.Article Citation - WoS: 12Citation - Scopus: 13Emission of the Thz Waves From Large Area Mesas of Superconducting Bi 2sr2cacu2o8+? by the Injection of Spin Polarized Current(Elsevier Ltd., 2013) Türkoğlu, Fulya; Özyüzer, Lütfi; Köseoğlu, Hasan; Demirhan, Yasemin; Preu, S.; Malzer, S.; Şimşek, Yılmaz; Wang, Huabing; Muller, P.Rectangular Au/Co/Au/Bi2Sr2CaCu2O 8+δ (Bi2212) mesa structures with large areas and high thicknesses were fabricated on as-grown Bi2212 single crystals in order to obtain small critical current from as-grown mesas by the injection of spin polarized current and so eliminate the adjustment of doping level for successful THz emission. We have performed c-axis resistance versus temperature (R-T), current-voltage (I-V) characteristics and bolometer measurements. It is the first time that THz emission has been observed from as-grown mesas due to injection of spin polarized current. © 2013 Elsevier Ltd. All rights reserved.Article Citation - WoS: 39Citation - Scopus: 40Interferometer Measurements of Terahertz Waves From Bi 2sr 2cacu 2o 8+d Mesas(IOP Publishing Ltd., 2012) Türkoğlu, Fulya; Köseoğlu, Hasan; Demirhan, Yasemin; Özyüzer, Lütfi; Preu, Sascha; Malzer, Stefan; Şimşek, Yusuf; Müller, P.; Yamamoto, T.; Kadowaki, K.We fabricated rectangular mesa structures of superconducting Bi 2Sr 2CaCu 2O 8+d (Bi2212) using e-beam lithography and Ar ion beam etching techniques for terahertz (THz) emission. c-axis resistance versus temperature (R-T), current-voltage (I-V) characteristics and bolometric THz power measurements were performed to characterize Bi2212 mesas. The emission frequency of mesas was determined using a Michelson interferometer setup which also demonstrates polarized emission. Interference patterns of THz radiation from Bi2212 mesas were detected by various detectors such as a liquid helium cooled silicon composite bolometer, a Golay cell and a pyroelectric detector. An emitted power as high as 0.06mW was detected from Bi2212 mesas. For the first time, most of the pumped power was extracted as THz emission from a Bi2212 mesa. The radiation at 0.54THz was detected using the Michelson interferometric setup.Conference Object Fabrication of Double Mesa Structures by E-Beam Lithography From High Temperature Superconducting Bi2sr2cacu2o 8+? (bi2212) for Powerful Terahertz Emission(Institute of Electrical and Electronics Engineers Inc., 2011) Demirhan, Yasemin; Türkoğlu, Fulya; Köseoğlu, Hasan; Minematsu, M.; Araki, H.; Miyakawa, Nobuaki; Özyüzer, LütfiWe work on a frequency tunable solid state device to meet the needs of continuous, coherent, powerful terahertz emission sources that fill practically important terahertz gap. High temperature superconducting (HTS) coherently oscillating Josephson junctions in Bi2Sr2CaCu 2O8+δ (Bi2212) crystal make this approach very promising. Since doping dependence of Bi2212 is an important parameter, Bi2212 crystals are annealed in vacuum or purified argon gas flow at 425°C. For further processing we pattern both single and double rectangular mesa structures by using electron beam lithography on the cleaved surface of the crystal. Resistance-temperature (R-T), and current-voltage behavior (I-V) measurements achieved. © 2011 IEEE.Conference Object Terahertz Wave Emission From Layered Superconductors: Interferometer Measurements(Institute of Electrical and Electronics Engineers Inc., 2011) Özyüzer, Lütfi; Türkoğlu, Fulya; Demirhan, Yasemin; Köseoğlu, Hasan; Preu, S.; Ploss, D.; Malzer, S.; Şimşek, Yılmaz; Wang, Huabing; Müller, P.Rectangular Bi2Sr2CaCu2O 8+δ (Bi2212) mesa structures were fabricated on as-grown Bi2212 single crystal superconductors using standard photolithography and Ar ion beam etching techniques. We have performed c-axis resistance versus temperature (R-T), current-voltage (I-V) characteristics and bolometer measurements. Furthermore, in contrast to previous studies, the emission frequency was determined using interferometer set up instead of FTIR. The interference patterns were detected outside the cryostat after traveling long way through ambient space. The emission frequency calculated by Fourier transform of interference data is consistent with Josephson frequency-voltage relation. © 2011 IEEE.