62 results on '"Bayram Butun"'
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2. Ultra-broadband, wide angle absorber utilizing metal insulator multilayers stack with a multi-thickness metal surface texture
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Amir Ghobadi, Sina Abedini Dereshgi, Hodjat Hajian, Berkay Bozok, Bayram Butun, and Ekmel Ozbay
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Medicine ,Science - Abstract
Abstract In this paper, we propose a facile route to fabricate a metal insulator multilayer stack to obtain ultra-broadband, wide angle behavior from the structure. The absorber, which covers near infrared (NIR) and visible (Vis) ranges, consists of a metal-insulator-metal-insulator (MIMI) multilayer where the middle metal layer has a variant thickness. It is found that this non-uniform thickness of the metal provides us with an absorption that is much broader compared to planar architecture. In the non-uniform case, each thickness is responsible for a specific wavelength range where the overall absorption is the superposition of these resonant responses and consequently a broad, perfect light absorption is attained. We first numerically examine the impact of different geometries on the overall light absorption property of the multilayer design. Afterward, we fabricate the designs and characterize them to experimentally verify our numerical findings. Characterizations show a good agreement with numerical results where the optimum absorption bandwidth for planar design is found to be 620 nm (380 nm–1000 nm) and it is significantly boosted to an amount of 1060 nm (350 nm–1410 nm) for multi-thickness case.
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- 2017
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3. Impact of the Low Temperature Ohmic Contact Process on DC and Forward Gate Bias Stress Operation of GaN HEMT Devices
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Oguz Odabasi, Amir Ghobadi, Turkan Gamze Ulusoy Ghobadi, Yakup Unal, Gurur Salkim, Gunes Basar, Bayram Butun, Ekmel Ozbay, Odabaşı, Oğuz, Ghobadi, Amir, Ghobadi, Türkan Gamze Ulusoy, Ünal, Yakup, Salkım, Gurur, Başar, Güneş, Bütün, Bayram, and Özbay, Ekmel
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Surface roughness ,Stabil15 ity ,AlGaN/GaN HEMTs ,Recessed 16 ohmic contacts ,Electrical and Electronic Engineering ,Ohmic contact ,Annealing temperatures ,Electronic, Optical and Magnetic Materials - Abstract
In AlGaN/GaN high electron mobility transistors (HEMTs), high temperature processes (such as ohmic annealing with >800°C value) could deform the crystal structure and induce trap states within the bulk and surface. Expanded defect densities cause crucial problems, such as threshold voltage ( Vth ) instability, current collapse, and high leakages. In this work, a low temperature ohmic contact process (630°C, 10 minutes) is adopted with recess etch, and contact resistances
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- 2022
4. Fast Unveiling of T max in GaN HEMT Devices via the Electrical Measurement-Assisted Two-Heat Source Model
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Hasan Kocer, Yilmaz Durna, Burak Gunes, Gizem Tendurus, Bayram Butun, Ekmel Ozbay, Koçer, Hasan, Durna, Yılmaz, Güneş, Burak, Tendürüs, Gizem, Bütün, Bayram, and Özbay, Ekmel
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Finite element analysis (FEA) ,High-electron-mobility transistors (HEMTs) ,Thermal analysis ,Electrical and Electronic Engineering ,Electronic, Optical and Magnetic Materials - Abstract
Gallium nitride (GaN) high-electron-mobility transistor (HEMT) devices, which have wide application potential from power amplifiers to satellite, need to be thoroughly examined in terms of reliability in order to benefit the superior intrinsic properties of the device. The most critical parameter in the device reliability is the hotspot, or Tmax , which occurs somewhere on the subsurface and along the channel of the GaN HEMT, which is optically inaccessible due to optical path disability. Therefore, the Tmax value is underestimated in optical measurements, such as the thermographic IR and Raman methods. With 3-D electrothermal simulations, Tmax is obtained close to reality, but it requires a huge computation load and the complex modeling of semiconductor device physics. In 2-D or 3-D thermal simulations that do not use electrothermal simulations, since the self-heating is mostly modeled with a single heat source, neither the correct Tmax value is obtained nor the effect of bias conditions is considered. To address the aforementioned shortcomings, a hybrid method is demonstrated, which exploits the electrical measurements of GaN HEMT, which RF and reliability engineers often and easily do. It is demonstrated that Tmax can be determined quickly and close to the electrothermal simulations in a GaN HEMT device with a two-heat source method and finite element analysis (FEA) hybrid interaction with respect to various bias conditions. Moreover, the impact of the knee voltage is investigated with different knee-detection techniques. The proposed method provides GaN HEMT reliability engineers with an easy-to-implement alternative to reveal the hotspot location and the value.
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- 2022
5. Unveiling Tmax inside GaN HEMT based X-band low-noise amplifier by correlating thermal simulations and IR thermographic measurements
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Salahuddin Zafar, Yilmaz Durna, Hasan Kocer, Busra Cankaya Akoglu, Yunus Erdem Aras, Oguz Odabasi, Bayram Butun, Ekmel Ozbay, Zafar, Salahuddin, Durna, Yılmaz, Koçer, Hasan, Akoğlu, Büşra Çankaya, Aras, Yunus Erdem, Bütün, Bayram, and Özbay, Ekmel
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MMIC ,Finite element analysis ,IR imaging ,Low-noise amplifier ,Electrical and Electronic Engineering ,Safety, Risk, Reliability and Quality ,HEMT ,Electronic, Optical and Magnetic Materials - Abstract
This paper presents a method to reveal the channel temperature profile of high electron mobility transistors (HEMTs) in a multi-stage monolithic microwave integrated circuit (MMIC). The device used for this study is a two-stage X-band low-noise amplifier fabricated using 0.15 m GaN-on-SiC technology with 4x50 m and 4x75 m HEMTs at the first and the second stage, respectively. The surface temperature measured through infrared (IR) thermography has a diffraction-limited resolution. Moreover, it is impossible to measure sub-surface Tmax residing inside the two-dimensional electron gas of HEMT using IR thermographic measurements. Finite element analysis (FEA) thermal simulations are performed in this study to acquire the surface and sub-surface temperature profiles of the whole MMIC. IR measurements and FEA simulations are integrated through a correlation-based method verifying the accuracy of the FEA-based temperature profiles. This method leads to accurately finding the hotspots in the MMIC, thus revealing the Tmax of both stages. The correlation method using two filters approach to match the measurements and simulated temperature profiles of all the stages finds its application in MMICs’ high-temperature operating lifetime reliability tests.
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- 2022
6. Ultrathin interfacial layer and pre-gate annealing to suppress virtual gate formation in GaN-based transistors: The impact of trapping and fluorine inclusion
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Oguz Odabasi, Amir Ghobadi, Turkan Gamze Ulusoy Ghobadi, Bayram Butun, Ekmel Ozbay, Odabaşı, Oğuz, Ghobadi, Amir, Ghobadi, Türkan Gamze Ulusoy, and Özbay, Ekmel
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Passivation ,Transistor ,AlGaN/GaN HEMT ,Electrical and Electronic Engineering ,15 lag phenomena ,Stability ,Electronic, Optical and Magnetic Materials - Abstract
In AlGaN/GaN high electron mobility transistors (HEMTs), the long-term operation of the device is adversely affected by threshold voltage ( Vth ) instability and current collapse. In this letter, using structural and electrical analyses, the impact of trapping and fluorine (F) inclusion on the device operation is scrutinized. It is found that SiNx interfacial layer significantly reduced the formation of defects, during the ohmic annealing process. Moreover, the incorporation of F ions into GaN bulk, during the gate etch process, triggers the virtual gate phenomenon. This effect has also been mitigated via the pre-gate annealing (PGA) process. As a result of these modifications, a stable operation with minimized lag performance has been achieved.
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- 2022
7. Correlation-based study of FEA and IR thermography to reveal the 2DEG temperature of a multi-fingered high-power GaN HEMT
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Yilmaz Durna, Hasan Kocer, Yunus Erdem Aras, Mahmut Can Soydan, Bayram Butun, Ekmel Ozbay, Durna, Yılmaz, Koçer, Hasan, Aras, Yunus Erdem, Soydan, Mahmut Can, Butun, Bayram, and Özbay, Ekmel
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General Physics and Astronomy - Abstract
High electron mobility transistors (HEMTs) based on gallium nitride (GaN) with a wide range of application potentials need to be rigorously examined for reliability to take advantage of their intrinsically extraordinary properties. The most vital parameter of the reliability, the hotspot, or Tmax, resides in the two-dimensional electron gas (2DEG) temperature profile inside the device where optical access is often restricted. The device surface temperature can be measured by widespread IR thermography with the limitation of diffraction-based IR transmission losses. However, Tmax on the sub-surface cannot be reached thermographically. Although finite element analysis (FEA)-based thermal simulations can easily reveal the 2DEG temperature profile, accuracy is tightly dependent on the realistic modeling of material/structure parameters. Because these parameters are rather sensitive to fabrication and processing, it is quite difficult to specify them accurately. To overcome these drawbacks, a method integrating both IR thermography and FEA thermal analysis is demonstrated on a fabricated high-power 40 × 360 μm packaged GaN HEMT as a proof-of-concept. Utilizing the simulation and measurement temperature profiles, a correlation algorithm is developed so that accuracy of the FEA thermal simulation is improved by calibrating the parameters specific to fabrication/process conditions by thermographic measurement. Then, it is quantitatively shown that the proposed method is able to find the 2DEG temperature profile and Tmax with an accuracy that best suits the intrinsic and extrinsic characteristics of the device under test. The method sheds light on GaN reliability engineering by providing a feasible and reliable alternative to realistically reveal hotspot information for device lifetime assessments.
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- 2022
8. Improved T MAX Estimation in GaN HEMTs Using an Equivalent Hot Point Approximation
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Mehmet Omer Akar, Oguz Odabasi, Bayram Butun, Ekmel Ozbay, Odabaşı, Oğuz, Akar, Mehmet Ömer, Bütün, Bayram, and Özbay, Ekmel
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Work (thermodynamics) ,Thermal resistance ,Selfheating ,2-D device simulations ,01 natural sciences ,law.invention ,law ,Hot point ,0103 physical sciences ,Hardware_INTEGRATEDCIRCUITS ,Point (geometry) ,Finite-element analysis ,Thermal analysis ,Electrical and Electronic Engineering ,010302 applied physics ,Physics ,Transistor ,Technology computer-aided design (TCAD) ,High-electron-mobility transistors (HEMTs) ,Finite element method ,Electronic, Optical and Magnetic Materials ,Computational physics ,Distribution (mathematics) ,AlGaN ,Gallium nitride (GaN) ,Heat generation ,Channel temperature - Abstract
In this article, heat generation distribution and maximum device temperature of gallium-nitride (GaN) high-electron-mobility transistors (HEMTs) are investigated by using the 2-D electrothermal and finite-element method (FEM) simulations. Devices with different gate lengths and source-to-drain spacing are investigated. It is observed that the maximum device temperature (TMAX) depends on the drain-to-source spacing and is almost independent of the gate length and that the assumption of a uniform heat generation region, under the gate, is not accurate; this is contrary to conventional calculation methods. Moreover, based on the results, a new approximation is proposed to use in the FEM simulations that can estimate TMAX more accurately. This method does not require physics-based technology computer-aided design (TCAD) simulations and can work with a low mesh density. The performance is compared with prior methods. This work was supported by Turkish Scientific and Technological Research Council, TUBITAK, under 1501 project GaNTURK. The work of Ekmel Özbay was supported in part by the Turkish Academy of Sciences.
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- 2020
9. Strong Interference in Planar, Multilayer Perfect Absorbers: Achieving High-Operational Performances in Visible and Near-Infrared Regimes
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Hodjat Hajian, Bayram Butun, Ekmel Ozbay, Amir Ghobadi, Ghobadi, Amir, Hajian, Hodjat, Bütün, Bayram, and Özbay, Ekmel
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Materials science ,Nanophotonics ,Optical device fabrication ,02 engineering and technology ,01 natural sciences ,Absorption ,law.invention ,010309 optics ,Planar ,Optics ,Interference (communication) ,law ,0103 physical sciences ,Broadband ,Black-body radiation ,Electrical and Electronic Engineering ,Absorption (electromagnetic radiation) ,Cavity resonators ,Ideal (set theory) ,Nonhomogeneous media ,business.industry ,Photovoltaic cells ,Mechanical Engineering ,Optical design ,Nanostructured materials ,021001 nanoscience & nanotechnology ,Anti-reflective coating ,Metals ,0210 nano-technology ,business - Abstract
Light-Matter Interactions at subwavelength-designed nanostructures have been the subject of intensive study in recent years. The realization of an ideal "blackbody" absorber is an emerging topic in nanophotonics and nanoplasmonics. An ideal black absorber is an object that harvests incoming light with near-unity efficiency. Based on their absorption spectral coverage, they are classified as narrow-band or broadband absorbers. This requirement can be achieved in bulky designs that have a thickness much larger than its light penetration depth as well as antireflective surface texturing.
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- 2019
10. Spectrally Selective Ultrathin Photodetectors Using Strong Interference in Nanocavity Design
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Ekmel Ozbay, Bayram Butun, Amir Ghobadi, Yigit Demirag, Hodjat Hajian, Ahmet Toprak, Ghobadi, Amir, Demirağ, Yiğit, Hajian, Hodjat, Toprak, Ahmet, Bütün, Bayram, and Özbay, Ekmel
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Optical devices ,010302 applied physics ,Amorphous silicon ,Materials science ,Semiconductor metamaterials ,business.industry ,Photodetectors ,Photodetector ,medicine.disease_cause ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Active layer ,chemistry.chemical_compound ,Responsivity ,Semiconductor ,chemistry ,Interference (communication) ,0103 physical sciences ,medicine ,Optoelectronics ,Perfect absorbers ,Electrical and Electronic Engineering ,business ,Absorption (electromagnetic radiation) ,Ultraviolet - Abstract
Thinning the active layer’s thickness of the semiconductor down to a level comparable with the carriers’ diffusion length while keeping its absorption high is an ultimate goal to boost the performance of optoelectronic devices. Strong interference in multilayer structures is one of the promising and practical solutions owing to their simple and large-scale compatible fabrication route. These nanocavity designs not only provide near unity absorption, but they can also be designed in a way that a spectrally selective absorption response can be achieved. In this letter, we will demonstrate the functionality of a metal–insulator–semiconductor (MIS) cavity to obtain spectrally selective ultrathin photodetectors. To prove our theoretical and numerical findings, a 4-nm-thick amorphous silicon (a-Si)-based MIS cavity is designed, fabricated, and characterized. The experimental results show that the optimized cavity design can act as an efficient visible blind ultraviolet (UV) photodetector. The proposed design shows the responsivity values of 120 and 2.5 mA/W in the UV ( $\lambda =\textsf {350}$ nm) and visible ( $\lambda =\textsf {500}$ nm) regions, respectively.
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- 2019
11. Bismuth-based metamaterials: from narrowband reflective color filter to extremely broadband near perfect absorber
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Amir Ghobadi, Ekmel Ozbay, Murat Gokbayrak, Hodjat Hajian, Bayram Butun, Ghobadi, Amir, Hajian, Hodjat, Gökbayrak, Murat, Bütün, Bayram, and Özbay, Ekmel
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Materials science ,QC1-999 ,Color filter ,perfect absorber ,Impedance matching ,chemistry.chemical_element ,Physics::Optics ,02 engineering and technology ,Nanomaterials ,Bismuth ,Solar irradiation ,03 medical and health sciences ,Narrowband ,Plasmonic resonance ,Color gel ,Broadband ,Electrical and Electronic Engineering ,030304 developmental biology ,0303 health sciences ,Perfect absorber ,impedance matching ,business.industry ,Physics ,plasmonic resonance ,Metamaterial ,solar irradiation ,021001 nanoscience & nanotechnology ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,metamaterials ,chemistry ,color filter ,Metamaterials ,Optoelectronics ,0210 nano-technology ,business ,Biotechnology - Abstract
In recent years, sub-wavelength metamaterials-based light perfect absorbers have been the subject of many studies. The most frequently utilized absorber configuration is based on nanostructured plasmonic metals. However, two main drawbacks were raised for this design architecture. One is the fabrication complexity and large scale incompatibility of these nano units. The other one is the inherent limitation of these common metals which mostly operate in the visible frequency range. Recently, strong interference effects in lithography-free planar multilayer designs have been proposed as a solution for tackling these drawbacks. In this paper, we reveal the extraordinary potential of bismuth (Bi) metal in achieving light perfect absorption in a planar design through a broad wavelength regime. For this aim, we adopted a modeling approach based on the transfer matrix method (TMM) to find the ideal conditions for light perfect absorption. According to the findings of our modeling and numerical simulations, it was demonstrated that the use of Bi in the metal-insulator-metal-insulator (MIMI) configuration can simultaneously provide two distinct functionalities; a narrow near unity reflection response and an ultra-broadband near perfect absorption. The reflection behavior can be employed to realize additive color filters in the visible range, while the ultra-broadband absorption response of the design can fully harvest solar irradiation in the visible and near infrared (NIR) ranges. The findings of this paper demonstrate the extraordinary potential of Bi metal for the design of deep sub-wavelength optical devices.
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- 2019
12. Algan/Gan-Based Laterally Gated High-Electron-Mobility Transistors With Optimized Linearity
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Erdem Aras, Busra Cankaya Akoglu, Bayram Butun, Kubra Elif Asan, Dogan Yilmaz, Ekmel Ozbay, Oguz Odabasi, Salahuddin Zafar, Odabaşı, Oğuz, Yılmaz, Doğan, Aras, Erdem, Asan, Kübra Elif, Zafar, Salahuddin, Çankaya Akoğlu, Büşra, Bütün, Bayram, and Özbay, Ekmel
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Power gain ,Materials science ,AlGaN/GaN high-electron-mobility transistors (HEMTs) ,Laterally gated HEMT ,Transconductance ,FinHEMT ,Field-effect transistors (FETs) ,Hardware_PERFORMANCEANDRELIABILITY ,Span (engineering) ,01 natural sciences ,law.invention ,Planar ,Linearity ,law ,0103 physical sciences ,Hardware_INTEGRATEDCIRCUITS ,Electrical and Electronic Engineering ,010302 applied physics ,business.industry ,Transistor ,Buried gate ,Tri-gate ,Electronic, Optical and Magnetic Materials ,Logic gate ,FinFET ,Optoelectronics ,business ,Electron-beam lithography ,Hardware_LOGICDESIGN - Abstract
In this work, highly linear AlGaN/GaN laterally gated (or buried gate) high-electron-mobility transistors (HEMTs) are reported. The effect of gate dimensions on source-access resistance and the linearity of laterally gated devices are investigated experimentally in detail for the first time. Transistors with different gate dimensions and conventional planar devices are fabricated using two-step electron beam lithography (EBL). Current–voltage, source-access resistance, small-signal, and two-tone measurements are performed to evaluate the linearity of devices. Contrary to conventional planar HEMTs, the intrinsic transconductance of laterally gated devices monotonically increases with increasing gate voltage, showing a similar behavior as junction field-effect transistors (FETs). The source-access resistance shows a polynomial increase with the drain current, which can be reduced by decreasing the filling ratio of the buried gates. Through the optimization of these two competing factors, i.e., intrinsic transconductance and the source-access resistance, flat transconductance with high linearity is achieved experimentally. The laterally gated structure shows flat transconductance and small-signal power gain over a larger span of gate voltage that is 2.5 times higher than a planar device. Moreover, 6.9-dB improvement in output intercept point (OIP3)/ ${P}_{\text {DC}}$ is achieved. This approach can be used to improve the linearity of AlGaN/GaN HEMTs at the device level.
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- 2021
13. Strong light-matter interaction in lithography-free metamaterial perfect absorbers: energy conversion, color filtering, and sensing applications (Conference Presentation)
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Ekmel Ozbay, Bayram Butun, Amir Ghobadi, and Hodjat Hajian
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Physics ,business.industry ,Electromagnetic spectrum ,Physics::Optics ,Metamaterial ,medicine.disease_cause ,Wavelength ,Planar ,medicine ,Optoelectronics ,Energy transformation ,business ,Absorption (electromagnetic radiation) ,Lithography ,Ultraviolet - Abstract
The efficient harvesting of electromagnetic (EM) waves by sub-wavelength nanostructures can result in perfect light absorption in the narrow or broad frequency range. In recent years, the concept of lithography-free planar light perfect absorbers has attracted much attention in different parts of the EM spectrum, owing to their ease of fabrication and high functionality. In this talk, we will review the material and architecture requirements for the realization of light perfect absorption using these multilayer metamaterial designs from ultraviolet (UV) to far-infrared (FIR) wavelength regimes. We will summarize our latest studies on the use of metamaterial designs for energy conversion, filtering, and sensing applications using lithography-free light perfect absorbers. We will also discuss the progress, challenges, and outlook of this field to outline its future direction.
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- 2020
14. Tunable Plasmon-Phonon Polaritons In Anisotropic 2D Materials On Hexagonal Boron Nitride
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Ekmel Ozbay, Bayram Butun, George W. Hanson, Hodjat Hajian, Ivan D. Rukhlenko, Tony Low, Hajian, Hodjat, Bütün, Bayram, and Özbay, Ekmel
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Materials science ,topology ,Phonon ,QC1-999 ,Polaritons ,Physics::Optics ,Hexagonal boron nitride ,02 engineering and technology ,Topology ,In-plane anisotropy ,Nanomaterials ,03 medical and health sciences ,Condensed Matter::Materials Science ,hyperbolic ,Polariton ,Electrical and Electronic Engineering ,hexagonal boron nitride ,Anisotropy ,Plasmon ,Topology (chemistry) ,030304 developmental biology ,Hyperbolic ,0303 health sciences ,business.industry ,2d materials ,Physics ,021001 nanoscience & nanotechnology ,2D materials ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,in-plane anisotropy ,Optoelectronics ,0210 nano-technology ,business ,Biotechnology ,polaritons - Abstract
Mid-infrared (MIR) plasmon-phonon features of heterostructures composing of a plasmonic anisotropic two-dimensional material (A2DM) on a hexagonal boron nitride (hBN) film are analyzed. We derive the exact dispersion relations of plasmon-phonons supported by the heterostructures and demonstrate the possibility of topological transitions of these modes within the second Reststrahlen band of hBN. The topological transitions lead to enhanced local density of plasmon-phonon states, which intensifies the spontaneous emission rate, if the thickness of the hBN layer is appropriately chosen. We also investigate a lateral junction formed by A2DM/hBN and A2DM, demonstrating that one can realize asymmetric guiding, beaming, and unidirectionality of the hybrid guided modes. Our findings demonstrate potential capabilities of the A2DM/hBN heterostructures for active tunable light–matter interactions and asymmetric in-plane polariton nanophotonics in the MIR range.
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- 2020
15. Strong Light–Matter Interaction in Lithography-Free Planar Metamaterial Perfect Absorbers
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Hodjat Hajian, Amir Ghobadi, Bayram Butun, and Ekmel Ozbay
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Range (particle radiation) ,Nanostructure ,Materials science ,business.industry ,Physics::Optics ,Metamaterial ,02 engineering and technology ,Physics::Classical Physics ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,010309 optics ,Planar ,Computer Science::Multimedia ,0103 physical sciences ,Optoelectronics ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Broadband absorption ,Lithography ,Computer Science::Databases ,Plasmon ,Biotechnology - Abstract
The efficient harvesting of electromagnetic (EM) waves by subwavelength nanostructures can result in perfect light absorption in the narrow or broad frequency range. These metamaterial-based perfec...
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- 2018
16. Tailoring far-infrared surface plasmon polaritons of a single-layer graphene using plasmon-phonon hybridization in graphene-LiF heterostructures
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Hodjat Hajian, Amir Ghobadi, Andriy E. Serebryannikov, Ekmel Ozbay, Bayram Butun, Guy A. E. Vandenbosch, Yigit Demirag, Hajian, Hodjat, Ghobadi, Amir, Demirağ, Yiğit, Bütün, Bayram, and Özbay, Ekmel
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Permittivity ,Materials science ,lcsh:Medicine ,02 engineering and technology ,Dielectric ,Substrate (electronics) ,LIGHT-MATTER INTERACTION ,01 natural sciences ,Article ,law.invention ,RESONATORS ,law ,METAMATERIALS ,0103 physical sciences ,Figure of merit ,010306 general physics ,lcsh:Science ,Plasmon ,Multidisciplinary ,Science & Technology ,business.industry ,Graphene ,HEXAGONAL BORON-NITRIDE ,lcsh:R ,Heterojunction ,021001 nanoscience & nanotechnology ,Surface plasmon polariton ,Multidisciplinary Sciences ,MODES ,Optoelectronics ,Science & Technology - Other Topics ,lcsh:Q ,0210 nano-technology ,business - Abstract
Being one-atom thick and tunable simultaneously, graphene plays the revolutionizing role in many areas. The focus of this paper is to investigate the modal characteristics of surface waves in structures with graphene in the far-infrared (far-IR) region. We discuss the effects exerted by substrate permittivity on propagation and localization characteristics of surface-plasmon-polaritons (SPPs) in single-layer graphene and theoretically investigate characteristics of the hybridized surface-phonon-plasmon-polaritons (SPPPs) in graphene/LiF/glass heterostructures. First, it is shown how high permittivity of substrate may improve characteristics of graphene SPPs. Next, the possibility of optimization for surface-phonon-polaritons (SPhPs) in waveguides based on LiF, a polar dielectric with a wide polaritonic gap (Reststrahlen band) and a wide range of permittivity variation, is demonstrated. Combining graphene and LiF in one heterostructure allows to keep the advantages of both, yielding tunable hybridized SPPPs which can be either forwardly or backwardly propagating. Owing to high permittivity of LiF below the gap, an almost 3.2-fold enhancement in the figure of merit (FoM), ratio of normalized propagation length to localization length of the modes, can be obtained for SPPPs at 5-9 THz, as compared with SPPs of graphene on conventional glass substrate. The enhancement is efficiently tunable by varying the chemical potential of graphene. SPPPs with characteristics which strongly differ inside and around the polaritonic gap are found. ispartof: Scientific Reports vol:8 issue:1 ispartof: location:England status: published
- Published
- 2018
17. Ultra-broadband, wide angle absorber utilizing metal insulator multilayers stack with a multi-thickness metal surface texture
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Bayram Butun, Hodjat Hajian, Amir Ghobadi, Sina Abedini Dereshgi, Berkay Bozok, Ekmel Ozbay, and Özbay, Ekmel
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Materials science ,Science ,Geometry ,Insulator (electricity) ,02 engineering and technology ,Surface finish ,01 natural sciences ,Article ,010309 optics ,Metal ,Superposition principle ,Planar ,0103 physical sciences ,Broadband ,Light absorption ,Absorption (electromagnetic radiation) ,Infrared radiation ,Behavior ,Multidisciplinary ,business.industry ,Near-infrared spectroscopy ,021001 nanoscience & nanotechnology ,visual_art ,visual_art.visual_art_medium ,Optoelectronics ,Medicine ,Thickness ,0210 nano-technology ,business - Abstract
In this paper, we propose a facile route to fabricate a metal insulator multilayer stack to obtain ultra-broadband, wide angle behavior from the structure. The absorber, which covers near infrared (NIR) and visible (Vis) ranges, consists of a metal-insulator-metal-insulator (MIMI) multilayer where the middle metal layer has a variant thickness. It is found that this non-uniform thickness of the metal provides us with an absorption that is much broader compared to planar architecture. In the non-uniform case, each thickness is responsible for a specific wavelength range where the overall absorption is the superposition of these resonant responses and consequently a broad, perfect light absorption is attained. We first numerically examine the impact of different geometries on the overall light absorption property of the multilayer design. Afterward, we fabricate the designs and characterize them to experimentally verify our numerical findings. Characterizations show a good agreement with numerical results where the optimum absorption bandwidth for planar design is found to be 620 nm (380 nm–1000 nm) and it is significantly boosted to an amount of 1060 nm (350 nm–1410 nm) for multi-thickness case.
- Published
- 2017
18. Lithography-free, manganese-based ultrabroadband absorption through annealing-based deformation of thin layers into metal-air composites
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Bayram Butun, Amin Khavasi, Ekmel Ozbay, Majid Aalizadeh, Aalizadeh, Majid, Bütün, Bayram, and Özbay, Ekmel
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Fabrication ,Materials science ,Annealing (metallurgy) ,chemistry.chemical_element ,FOS: Physical sciences ,Physics::Optics ,02 engineering and technology ,Manganese ,Applied Physics (physics.app-ph) ,01 natural sciences ,010309 optics ,Metal ,0103 physical sciences ,Composite material ,Broadband absorption ,High absorption ,Lithography ,Condensed Matter - Materials Science ,Thin layers ,Materials Science (cond-mat.mtrl-sci) ,Physics - Applied Physics ,021001 nanoscience & nanotechnology ,Atomic and Molecular Physics, and Optics ,chemistry ,visual_art ,visual_art.visual_art_medium ,0210 nano-technology ,Optics (physics.optics) ,Physics - Optics - Abstract
Fabrication, characterization, and analysis of an ultra-broadband lithography-free absorber is presented. An over 94% average absorption is experimentally achieved in the wavelength range of 450-1400 nm. This ultra-broadband absorption is obtained by a simple annealed tri-layer metal-insulator-metal (MIM) configuration. The metal used in the structure is Manganese (Mn), which also makes the structure cost-effective. It is shown that the structure retains its high absorption for TM polarization, up to 70 degrees, and, for TE polarization, up to 50 degrees. Moreover, the physical mechanism behind this broadband absorption is explained. Being both lithography-free and cost-effective, the structure is a perfect candidate for large-area and mass production purposes., 8 pages, 3 figures
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- 2019
19. Strong light-matter interaction in lithography-free planar metamaterial perfect absorbers (Conference Presentation)
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Ekmel Ozbay, Bayram Butun, Hodjat Hajian, and Amir Ghobadi
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Physics ,Wavelength ,Planar ,Photovoltaics ,business.industry ,Electromagnetic spectrum ,Physics::Optics ,Metamaterial ,Photodetection ,business ,Absorption (electromagnetic radiation) ,Engineering physics ,Lithography - Abstract
The efficient harvesting of electromagnetic (EM) waves by sub-wavelength nanostructures can result in perfect light absorption in the narrow or broad frequency range. These metamaterial based perfect light absorbers are of particular interest in many applications, including thermal photovoltaics, photovoltaics, sensing, filtering, and photodetection applications. Although advances in nanofabrication have provided the opportunity to observe strong light-matter interaction in various optical nanostructures, the repeatability and upscaling of these nano units have remained a challenge for their use in large scale applications. Thus, in recent years, the concept of lithography-free planar light perfect absorbers has attracted much attention in different parts of the EM spectrum, owing to their ease of fabrication and high functionality. In this talk, we will explore the material and architecture requirements for the realization of light perfect absorption using these multilayer metamaterial designs from ultraviolet (UV) to far-infrared (FIR) wavelength regimes. We will provide a general theoretical formulation to find the ideal condition for achieving near unity light absorption. Later, these theoretical estimations will be coupled with findings of recent studies on light perfect absorbers to explore the physical phenomena and the limits of different materials and design architectures. These studies are categorized in three main class of materials; metals, semiconductors, and other types of materials. We will show that, by the use of proper material and design configuration, it is possible to realize these lithography-free light perfect absorbers in every portion of the EM spectrum. This, in turn, opens up the opportunity of the practical application of these perfect absorbers in large scale dimensions. In the last part of the talk, we will discuss the progress, challenges, and outlook of this field to outline its future direction.
- Published
- 2019
20. Normally-off p-GaN gate InAlN/GaN HEMTs grown on silicon substrates
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Sertaç Ural, Ömer Ahmet Kayal, Berkay Bozok, Bayram Butun, Mustafa Kemal Öztürk, Gokhan Kurt, Melisa Ekin Gulseren, Ekmel Ozbay, Gülseren, Melisa Ekin, Bozok, Berkay, Kurt, Gökhan, Kayal, Ömer Ahmet, Mustafa, Mustafa, Ural, Sertaç, Bütün, Bayram, and Ekmel, Ekmel
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Buffer leakage ,Resistive touchscreen ,Materials science ,InAlN, normally-off ,Silicon ,business.industry ,chemistry.chemical_element ,High-electron-mobility transistors (HEMTs) ,High-electron-mobility transistor ,Epitaxy ,Buffer (optical fiber) ,Threshold voltage ,GaN ,chemistry ,Optoelectronics ,Back-barrier ,business ,p-GaN gate ,Layer (electronics) ,Order of magnitude - Abstract
Date of Conference: 2-7 February 2019 Conference name: SPIE OPTO, 2019 A normally-off InAlN/GaN high electron mobility transistor (HEMT) on Si substrate with a p-GaN gate is reported. Devices are fabricated on two different epitaxial structures, one containing a high resistive GaN buffer layer and one containing an AlGaN back-barrier, and the threshold voltage, drain current density, and buffer leakage current are compared. With the epitaxial structure containing a high resistive GaN layer, normally-off operation with a threshold voltage of +0.5 V is achieved. The threshold voltage is further increased to +2 V with the AlGaN back-barrier, and the buffer leakage current was improved by over an order of magnitude. The Society of Photo-Optical Instrumentation Engineers (SPIE)
- Published
- 2019
21. VO2-hBN-graphene-based bi-functional metamaterial for mid-infrared bi-tunable asymmetric transmission and nearly perfect resonant absorption
- Author
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Guy A. E. Vandenbosch, Andriy E. Serebryannikov, Hodjat Hajian, Ekmel Ozbay, Bayram Butun, Amir Ghobadi, Hajian, Hodjat, Ghobadi, Amir, Bütün, Bayram, and Özbay, Ekmel
- Subjects
Materials science ,Graphene ,Phonon ,business.industry ,Metamaterial ,Physics::Optics ,Statistical and Nonlinear Physics ,Heterojunction ,02 engineering and technology ,Grating ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,law.invention ,010309 optics ,law ,0103 physical sciences ,Polariton ,Optoelectronics ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,business ,Refractive index ,Photonic crystal - Abstract
Bi-tunable asymmetric light transmission (AT) and nearly perfect resonant absorption functionalities are achieved by a Lorentz-reciprocal metamaterial for the operation at the mid-infrared (MIR) wavelengths and transverse magnetic polarization. The bi-tunable metamaterial with bi-functional features and a total thickness of 1.8 mu m is based on an hBN/graphene/hBN heterostructure that is bounded by a Ge grating on the upper side and a hybrid VO2/Au grating on the lower side. Through analytical calculations, we first investigate how the dispersion characteristics of the high-beta hyperbolic phonon polaritons of hBN can be controlled and hybridized through the insulator (i-VO2) to metal (m-VO2) transition of VO2 in a bare hBN/VO2 heterostructure. Then, at the absence of graphene and owing to the support of the hybridized high-beta modes, a broad and efficient AT with forward-to-backward contrast exceeding 40% is obtained by numerical calculations for the i-VO2 case, as the first functionality of the structure. Moreover, it is found that for the m-VO2 case, the device is no longer transmittive and a nearly perfect resonant absorption response, as the second functionality, is observed for backward illumination. Finally, by introducing multilayer graphene into the structure and considering the intermediate states of VO2 in the calculations, the bi-tunable transmission and absorption characteristics of the device are investigated. We believe the designed metamaterial is well-suited for MIR optical diodes, sensors, and thermal emitters. (c) 2019 Optical Society of America
- Published
- 2019
22. Tunable infrared asymmetric light transmission and absorption via graphene-hBN metamaterials
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Guy A. E. Vandenbosch, Hodjat Hajian, Amir Ghobadi, Andriy E. Serebryannikov, Ekmel Ozbay, Bayram Butun, Hajian, Hodjat, Ghobadi, Amir, Bütün, Bayram, and Özbay, Ekmel
- Subjects
Optical devices ,Materials science ,Infrared ,General Physics and Astronomy ,02 engineering and technology ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,Plasmon ,010302 applied physics ,Graphene ,business.industry ,Metamaterial ,021001 nanoscience & nanotechnology ,Polarization (waves) ,Surface plasmon polaritons ,Ray ,Surface plasmon polariton ,Wavelength ,Metamaterials ,Optoelectronics ,Plasmonics ,Phonons ,0210 nano-technology ,business - Abstract
We theoretically prove in this paper that using planar multilayer graphene-hexagonal boron nitride (hBN) metamaterials (GhMMs) can yield ultrabroadband and high-contrast asymmetric transmission (AT) and asymmetric absorption (AA) of light. The AA and AT features are obtained in the far-infrared (FIR) and mid-infrared (MIR) regions for normally incident light with transverse magnetic polarization. Here, the GhMMs are integrated with two asymmetric gratings of Ge and are composed of alternating multilayers of graphene (11 multilayers) and hBN layers (10 layers). Moreover, the total subwavelength thickness of the hybrid structures is about 3 mu m, being less than half of the free-space wavelength up to nearly 50 THz. This approach-which is similar to the one introduced by Xu and Lezec [Nat. Commun. 5, 4141 (2014)] for a passive hyperbolic metamaterial operating in the visible range-is based on the excitation of high-beta modes of the GhMM with different transmission characteristics. In addition to being ultrabroadband and high-contrast, AT and AA features of the proposed GhMMs can be actively tuned by varying the chemical potential of graphene. Furthermore, it is shown that an on-off switching of AT factor at FIR and selective tunability at MIR frequencies can be obtained via varying mu. Due to its subwavelength and planar configuration and active operation, these multilayer graphene-hBN metamaterials with AT and AA characteristics hold promise for integration with compact optical systems operating in the MIR and FIR ranges and are suitable for applications such as optical diodes, sensors, and thermal emitters. Published under license by AIP Publishing.
- Published
- 2019
23. Investigation Of Angstrom-Thick Aluminium Oxide Passivation Layers To Improve The Gate Lag Performance Of Gan Hemts
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Gokhan Kurt, Ekmel Ozbay, Turkan Gamze Ulusoy Ghobadi, Mustafa Kemal Öztürk, Gurur Salkim, Bayram Butun, Melisa Ekin Gulseren, Amir Ghobadi, Gülseren, Melisa Ekin, Kurt, Gökhan, Ulusoy Ghobadi, Türkan Gamze, Ghobadi, Amir, Salkım, Gurur, Öztürk, Mustafa, Bütün, Bayram, and Ekmel, Ekmel
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Dielectric ,Materials science ,Polymers and Plastics ,Passivation ,High-electron-mobility transistor ,GaN ,Biomaterials ,chemistry.chemical_compound ,Atomic layer deposition ,Gate lag ,HEMT ,Leakage (electronics) ,business.industry ,Metals and Alloys ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Threshold voltage ,chemistry ,AlGaN ,Aluminium oxide ,Optoelectronics ,business ,Current density - Abstract
In this paper, we report an angstrom-thick atomic layer deposited (ALD) aluminum oxide (Al2O3) dielectric passivation layer for an AlGaN/GaN high electron mobility transistor (HEMT). Our results show a 55% improvement in the gate lag performance of the design and a decrease by half in interface state density upon coating with two cycles of ALD Al2O3. DC characteristics such as current density, threshold voltage, and leakage currents were maintained. ALD Al2O3 passivation layers with thicknesses up to 10 nm were investigated. XPS analyses reveal that the first ALD cycles are sufficient to passivate GaN surface traps. This study demonstrates that efficient passivation can be achieved in atomic-scale with dimensions much thinner than commonly used bulk layers.
- Published
- 2019
24. Active metamaterial nearly perfect light absorbers: A review [Invited]
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Hodjat Hajian, Bayram Butun, Amir Ghobadi, Ekmel Ozbay, Hajian, Hodjat, Bütün, Bayram, and Özbay, Ekmel
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Materials science ,business.industry ,Surface plasmon ,Metamaterial ,Physics::Optics ,Statistical and Nonlinear Physics ,Photodetection ,01 natural sciences ,7. Clean energy ,Atomic and Molecular Physics, and Optics ,010309 optics ,Photovoltaics ,visual_art ,0103 physical sciences ,Electronic component ,visual_art.visual_art_medium ,Optoelectronics ,Photonics ,business ,Microwave ,Photonic crystal - Abstract
Achieving nearly perfect light absorption from the microwave to optical region utilizing metamaterials has begun to play a significant role in photonics and optoelectronics due to their vital applications in thermal emitters, thermal photovoltaics, photovoltaics, sensing, filtering, and photodetection. However, employing passive components in designing perfect absorbers based on metamaterials and photonic crystals imposes some limits on their spectral operation. In order to overcome those limits, extensive research has been conducted on utilizing different materials and mechanisms to obtain active metamaterial light absorbers. In this review paper, we investigate the recent progress in tunable and reconfigurable metamaterial light absorbers through reviewing different active materials and mechanisms, and we provide a perspective for their future development and applications. (C) 2019 Optical Society of America
- Published
- 2019
25. Lithography-Free Planar Band-Pass Reflective Color Filter Using A Series Connection Of Cavities
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Bayram Butun, Amir Ghobadi, Hodjat Hajian, Ekmel Ozbay, Mahmut Can Soydan, Ghobadi, Amir, Hajian, Hodjat, Soydan, Mahmut Can, Bütün, Bayram, and Özbay, Ekmel
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0301 basic medicine ,Materials science ,Transfer-matrix method (optics) ,lcsh:Medicine ,Article ,Nanocavities ,03 medical and health sciences ,0302 clinical medicine ,Planar ,Optics ,Band-pass filter ,Color gel ,lcsh:Science ,Nanophotonics and plasmonics ,Multidisciplinary ,business.industry ,lcsh:R ,Metamaterial ,030104 developmental biology ,Filter (video) ,Metamaterials ,High color ,lcsh:Q ,Color filter array ,business ,030217 neurology & neurosurgery - Abstract
In this article, a lithography-free multilayer based color filter is realized using a proper series connection of two cavities that shows relatively high efficiency, high color purity, and a wide view angle. The proposed structure is a metal-insulator-metal-insulator-semiconductor (MIMIS) design. To optimize the device performance, at the first step, transfer matrix method (TMM) modeling is utilized to find the right choices of materials for each layer. Simulations are carried out later on to optimize the geometries of the layers to obtain our desired colors. Finally, the optimized devices are fabricated and experimentally characterized to evaluate our modelling findings. The characterization results of the fabricated samples prove the successful formation of efficient and wide view angle color filters. Unlike previously reported FP based designs that act as a band-stop filter in reflection mode (absorbing a narrow frequency range and reflecting the rest of the spectrum), this design generates a specific color by reflecting a narrow spectral range and absorbing the rest of the spectrum. The findings of this work can be extended to other multilayer structures where an efficient connection of cavities in a tandem scheme can propose functionalities that cannot be realized with conventional FP resonators.
- Published
- 2019
26. Normally-Off Algan/Gan Mis-Hemt With Low Gate Leakage Current Using A Hydrofluoric Acid Pre-Treatment
- Author
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Gokhan Kurt, Turkan Gamze Ulusoy Ghobadi, Sertaç Ural, Ekmel Ozbay, Ömer Ahmet Kayal, Mustafa Kemal Öztürk, Bayram Butun, Mehmet Kabak, Melisa Ekin Gulseren, Kurt, Gökhan, Gülseren, Melisa Ekin, Ghobadi, Türkan Gamze Ulusoy, Ural, Sertaç, Kayal, Ömer Ahmet, Öztürk, Mustafa, Bütün, Bayram, Kabak, Mehmet, and Özbay, Ekmel
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Materials science ,Gate dielectric ,Oxide ,02 engineering and technology ,High-electron-mobility transistor ,Gate leakage current ,01 natural sciences ,Normally-off ,GaN ,chemistry.chemical_compound ,Hydrofluoric acid ,X-ray photoelectron spectroscopy ,0103 physical sciences ,Materials Chemistry ,Surface roughness ,Electrical and Electronic Engineering ,HEMT ,010302 applied physics ,business.industry ,Hysteresis ,Pre-treatment ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,chemistry ,Optoelectronics ,0210 nano-technology ,business ,Layer (electronics) - Abstract
We demonstrate the electrical performances of an AlGaN/GaN metal–insulator–semiconductor high electron mobility transistor (MIS-HEMT) with low gate leakage current (Ig). A low gate leakage current as low as the order of 10−11 A/mm was achieved from normally-off MIS-HEMT device (Vth = 2.16 V) with a partially recessed gate, fluorine treatment, and ALD Al2O3 gate dielectric layer. The gate leakage current decrease is attributed to the pre-treatment of the gate region with hydrofluoric acid (HF) and deionized water (DI) solution, which acts to remove the native oxide layer and thus decrease interface traps. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses demonstrate that the AlGaN surfaces are modified such that the surface roughness and native oxide introduced by the treatments used to achieve normally-off operation are remedied with the use of the pre-treatment.
- Published
- 2019
27. Colorimetric and near-absolute polarization-insensitive refractive-index sensing in all-dielectric guided-mode resonance based metasurface
- Author
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Murat Gokbayrak, Amir Ghobadi, Bayram Butun, Ahmet Toprak, Deniz Umut Yildirim, Ekmel Ozbay, Mahmut Can Soydan, Yıldırım, Deniz Umut, Ghobadi, Amir, Soydan, Mahmut Can, Gökbayrak, Murat, Toprak, Ahmet, Bütün, Bayram, and Özbay, Ekmel
- Subjects
Materials science ,Resonance structures ,Guided-mode resonance ,business.industry ,02 engineering and technology ,Dielectric ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Polarization (waves) ,01 natural sciences ,Quantum mechanics ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Optics ,Polarization ,Molecule ,Physical and Theoretical Chemistry ,0210 nano-technology ,business ,Thickness ,Layers ,Refractive index - Abstract
Colorimetric detection of target molecules with insensitivity to incident-light polarization has attracted considerable attention in recent years. This resulted from the ability to provide rapid output and reduced assay times as a result of color changes upon altering the environment that are easily distinguishable by the naked eye. In this paper, we propose a highly sensitive refractive-index sensor, utilizing the excitation of guided modes of a novel two-dimensional periodically modulated dielectric grating-waveguide structure. The optimized nanosensor can numerically excite guided-mode resonances with an ultranarrow linewidth (full width at half-maximum) of 0.58 nm. Sensitivity is numerically investigated by considering the deposition of dielectric layers on the structure. For a layer thickness of 30 nm, the maximum sensitivity reached as high as 110 nm/refractive index unit (RIU), resulting in a very high figure of merit of 190. The fabricated devices with 30 nm aluminum oxide and zinc oxide coatings achieved a maximum sensitivity of 235.2 nm/RIU with a linewidth of 19 nm. Colorimetric detection with polarization insensitivity is confirmed practically by a simple optical microscope. Samples with different coatings have been observed to have clearly distinct colors, while the color of each sample is nearly identical upon azimuthal rotation. Excellent agreement is obtained between the numerical and experimental results regarding the spectral position of the resonances and sensitivity. The proposed device is, therefore, highly promising in efficient, highly sensitive, almost lossless, and compact molecular diagnostics in the field of biomedicine with personalized, label-free, early point-of-care diagnosis and field analysis, drug detection, and environmental monitoring.
- Published
- 2019
28. Investigation Of A Hybrid Approach For Normally-Off Gan Hemts Using Fluorine Treatment And Recess Etch Techniques
- Author
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Mustafa Kemal Öztürk, Bayram Butun, Gokhan Kurt, Mehmet Kabak, Sertaç Ural, Ömer Ahmet Kayal, Melisa Ekin Gulseren, Gurur Salkim, Ekmel Ozbay, Gülseren, Melisa Ekin, Salkım, Gurur, Ural, Sertaç, Kayal, Ömer Ahmet, Öztürk, Mustafa, Bütün, Bayram, Özbay, Ekmel, and Kurt, Gökhan
- Subjects
Materials science ,recess etch ,chemistry.chemical_element ,High-electron-mobility transistor ,Epitaxy ,Recess etch ,Normally-off ,GaN ,law.invention ,law ,Enhancement-mode ,Electrical and Electronic Engineering ,HEMT ,business.industry ,Transistor ,Wide-bandgap semiconductor ,Normally off ,Hybrid approach ,fluorine plasma implantation ,Fluorine plasma implantation ,Electronic, Optical and Magnetic Materials ,Threshold voltage ,chemistry ,AlGaN ,Fluorine ,Optoelectronics ,lcsh:Electrical engineering. Electronics. Nuclear engineering ,business ,enhancement-mode ,lcsh:TK1-9971 ,Biotechnology - Abstract
A hybrid approach for obtaining normally off high electron mobility transistors (HEMTs) combining fluorine treatment, recess etch techniques, and AlGaN buffer was studied. The effects of process variations (recess etch depth and fluorine treatment duration) and epitaxial differences (AlGaN and carbon doped GaN buffers) on the DC characteristics of the normally off HEMTs were investigated. Two different epitaxial structures and three different process variations were compared. Epitaxial structures prepared with an AlGaN buffer showed a higher threshold voltage ( $V_{\mathrm {th}} = + 3.59 ~\text {V}$ ) than those prepared with a GaN buffer ( $V_{\mathrm {th}} = +1.85 ~\text {V}$ ).
- Published
- 2019
29. Bismuth plasmonics for extraordinary light absorption in deep sub-wavelength geometries
- Author
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Amir Ghobadi, Bayram Butun, Imre Ozbay, Gonul Turhan-Sayan, Ghobadi, Amir, and Bütün, Bayram
- Subjects
Permittivity ,Materials science ,business.industry ,Surface plasmon ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Bismuth ,010309 optics ,Resonator ,Optics ,Absorption edge ,chemistry ,0103 physical sciences ,Metamaterial absorber ,0210 nano-technology ,business ,Absorption (electromagnetic radiation) ,Plasmon - Abstract
In this Letter, we demonstrate an ultra-broadband metamaterial absorber of unrivaled bandwidth (BW) using extraordinary optical response of bismuth (Bi), which is the material selected through our novel analysis. Based on our theoretical model, we investigate the maximum metal–insulator–metal (MIM) cavity BW, achievable by any metal with known n-k data. We show that an ideal metal in such structures should have a positive real permittivity part in the near-infrared (NIR) regime. Contrary to noble and lossy metals utilized by most research groups in the field, this requirement is satisfied only by Bi, whose data greatly adhere to the ideal material properties predicted by our analysis. A Bi nanodisc-based MIM resonator with an absorption above 0.9 in an ultra-broadband range of 800 nm–2390 nm is designed, fabricated, and characterized. To the best of our knowledge, this is the broadest absorption BW reported for a MIM cavity in the NIR with its upper-to-lower absorption edge ratio exceeding best contenders by more than 150%. According to the findings in this Letter, the use of proper materials and dimensions will lead to realization of deep sub-wavelength efficient optical devices.
- Published
- 2020
30. Metal-insulator-metal multilayer-based ultra-broadband perfect absorbers: from non-uniform texturing to nano-hole plasmonic units (Conference Presentation)
- Author
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Bayram Butun, Ekmel Ozbay, and Amir Ghobadi
- Subjects
Materials science ,business.industry ,Nano ,Broadband ,Optoelectronics ,Metal-insulator-metal ,business ,Plasmon - Published
- 2018
31. Tunable, omnidirectional, and nearly perfect resonant absorptions by a graphene-hBN-based hole array metamaterial
- Author
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Bayram Butun, Hodjat Hajian, Ekmel Ozbay, Amir Ghobadi, Hajian, Hodjat, Ghobadi, Amir, Bütün, Bayram, and Özbay, Ekmel
- Subjects
Total internal reflection ,Materials science ,business.industry ,Graphene ,Metamaterial ,Physics::Optics ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,01 natural sciences ,Surface plasmon polariton ,Atomic and Molecular Physics, and Optics ,law.invention ,010309 optics ,Optics ,law ,0103 physical sciences ,Polariton ,Physics::Atomic and Molecular Clusters ,Optoelectronics ,0210 nano-technology ,business ,Plasmon ,Photonic crystal - Abstract
In this paper, we propose an electrically tunable mid-infrared plasmonic-phononic absoiber with omnidirectional and polarization insensitive nearly perfect resonant absorption characteristics. The absorber consists of a graphene/hexagonal boron nitride (hBN)/graphene multilayer on top of a gold bottom reflector separated by a dielectric spacer. The graphene/hBN/graphene multilayer is patterned as a hole array in square lattice. We analytically and numerically prove that, due to the support of hybrid plasmon-phononpolaritons, nearly perfect multi-resonant absorption peaks with high quality factors are obtained both inside and outside of the Reststrahlen band of hBN. As a result of the hybridization of graphene plasmons with the hyperbolic phonon polaritons of hBN, the high quality resonant absorptions of the metamaterial are almost unaffected by decreasing the phenomenological electron relaxation time of graphene. Moreover, the obtained resonances can be effectively tuned in practice due to the continuity of the graphene layers in the hole array metamatenal. These features make the graphene-hBN metamaterial a skeptical design for practical purposes and mid-infrared multi-functional operations such as sensing. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
- Published
- 2018
32. Large-Area, Cost-Effective, Ultra-Broadband Perfect Absorber Utilizing Manganese In Metal-Insulator-Metal Structure
- Author
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Bayram Butun, Amin Khavasi, Ekmel Ozbay, Majid Aalizadeh, and Özbay, Ekmel
- Subjects
Materials science ,lcsh:Medicine ,chemistry.chemical_element ,02 engineering and technology ,Metal-insulator-metal ,Manganese ,01 natural sciences ,Article ,010309 optics ,Metal ,0103 physical sciences ,Broadband ,lcsh:Science ,Absorption (electromagnetic radiation) ,Lithography ,Multidisciplinary ,business.industry ,lcsh:R ,Metamaterial ,021001 nanoscience & nanotechnology ,Wavelength ,chemistry ,visual_art ,visual_art.visual_art_medium ,Optoelectronics ,lcsh:Q ,0210 nano-technology ,business - Abstract
Achieving broadband absorption has been a topic of intensive research over the last decade. However, the costly and time consuming stage of lithography has always been a barrier for the large-area and mass production of absorbers. In this work, we designed, fabricated, and characterized a lithography-free, large-area compatible, omni-directional, ultra-broadband absorber that consists of the simplest geometrical configuration for absorbers: Metal-Insulator-Metal (MIM). We introduced and utilized Manganese (Mn) for the first time as a very promising metal for broadband absorption applications. We optimized the structure step-by-step and compared Mn against the other best candidates introduced so far in broadband absorption structures and showed the better performance of Mn compared to them. It also has the advantage of being cheaper compared to metals like gold that has been utilized in many patterned broadband absorbers. We also presented the circuit model of the structure. We experimentally achieved over 94 percent average absorption in the range of 400–900 nm (visible and above) and we obtained absorption as high as 99.6 percent at the wavelength of 626.4 nm. We also experimentally demonstrated that this structure retains broadband absorption for large angles up to 70 degrees.
- Published
- 2018
33. Visible light nearly perfect absorber: an optimum unit cell arrangement for near absolute polarization insensitivity
- Author
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Hodjat Hajian, Ahmet Toprak, Murat Gokbayrak, Sina Abedini Dereshgi, Bayram Butun, Amir Ghobadi, and Ekmel Ozbay
- Subjects
Metal insulator metals ,Polarization insensitivity ,Materials science ,Light ,Metal patch ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,010309 optics ,Resonator ,Optics ,Polarization ,0103 physical sciences ,Surface plasmon resonance ,Visible light ,MIM devices ,Perfect absorber ,business.industry ,Ultra-broadband ,Near-field optics ,021001 nanoscience & nanotechnology ,Polarization (waves) ,Atomic and Molecular Physics, and Optics ,Unit cells ,Metal insulator boundaries ,Absorption bandwidth ,0210 nano-technology ,business ,Refractive index ,Electron-beam lithography ,Visible spectrum - Abstract
In this work, we propose an optimum unit cell arrangement to obtain near absolute polarization insensitivity in a metal-insulator-metal (MIM) based ultra-broadband perfect absorber. Our findings prove that upon utilizing this optimum arrangement, the response of the absorber is retained and unchanged over all arbitrary incidence light polarizations, regardless of the shape of the top metal patch. First, the impact of the geometry of the top nanopatch resonators on the absorption bandwidth of the overall structure is explored. Then, the response of the MIM design for different incidence polarizations and angles is scrutinized. Finally, the proposed design is fabricated and characterized. (C) 2017 Optical Society of America
- Published
- 2017
34. Ultra-Broadband, Lithography-Free, and Large-Scale Compatible Perfect Absorbers: The Optimum Choice of Metal layers in Metal-Insulator Multilayer Stacks
- Author
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Hodjat Hajian, Bayram Butun, Sina Abedini Dereshgi, Amir Ghobadi, Ekmel Ozbay, and Özbay, Ekmel
- Subjects
Materials science ,Transfer-matrix method (optics) ,Impedance matching ,lcsh:Medicine ,chemistry.chemical_element ,02 engineering and technology ,Tungsten ,01 natural sciences ,Article ,010309 optics ,Material selection ,0103 physical sciences ,lcsh:Science ,Absorption (electromagnetic radiation) ,Lithography ,Multidisciplinary ,business.industry ,lcsh:R ,Metamaterial ,021001 nanoscience & nanotechnology ,chemistry ,Optoelectronics ,lcsh:Q ,0210 nano-technology ,business ,Layer (electronics) - Abstract
We report ultra-broadband perfect absorbers for visible and near-infrared applications that are based on multilayers of metal-insulator (MI) stacks fabricated employing straightforward layer deposition techniques and are, therefore, lithography-free and large-scale compatible. We scrutinize the impact of different physical parameters of an MIMI absorber structure with analysis of each contributing metal layer. After obtaining the optimal design parameters (i.e. material selection and their thicknesses) with both simulation and numerical analysis (Transfer Matrix Method) methods, an experimental sample is fabricated and characterized. Our fabricated MIMI absorber consists of an optically thick tungsten (W) back reflector layer followed by 80 nm aluminum oxide (Al2O3), 10 nm titanium (Ti), and finally another 80 nm Al2O3. The experimental results demonstrate over 90 percent absorption between 400 nm and 1640 nm wavelengths that is optimized for ultra-broadband absorption in MIMI structures. Moreover, the impedance matching method with free-space is used to shed light on the metallic layer selection process.
- Published
- 2017
35. Disordered Nanohole Patterns in Metal-Insulator Multilayer for Ultra-broadband Light Absorption: Atomic Layer Deposition for Lithography Free Highly repeatable Large Scale Multilayer Growth
- Author
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Bayram Butun, Sina Abedini Dereshgi, Hodjat Hajian, Amir Ghobadi, Ekmel Ozbay, Berkay Bozok, and Özbay, Ekmel
- Subjects
Materials science ,Fabrication ,lcsh:Medicine ,02 engineering and technology ,01 natural sciences ,Article ,010309 optics ,Atomic layer deposition ,Planar ,Stack (abstract data type) ,0103 physical sciences ,lcsh:Science ,Absorption (electromagnetic radiation) ,Lithography ,Plasmon ,Nanophotonics and plasmonics ,Multidisciplinary ,business.industry ,lcsh:R ,021001 nanoscience & nanotechnology ,Metamaterials ,Optoelectronics ,lcsh:Q ,0210 nano-technology ,business ,Layer (electronics) ,Sub-wavelength optics - Abstract
In this paper, we demonstrate a facile, lithography free, and large scale compatible fabrication route to synthesize an ultra-broadband wide angle perfect absorber based on metal-insulator-metal-insulator (MIMI) stack design. We first conduct a simulation and theoretical modeling approach to study the impact of different geometries in overall stack absorption. Then, a Pt-Al2O3 multilayer is fabricated using a single atomic layer deposition (ALD) step that offers high repeatability and simplicity in the fabrication step. In the best case, we get an absorption bandwidth (BW) of 600 nm covering a range of 400 nm–1000 nm. A substantial improvement in the absorption BW is attained by incorporating a plasmonic design into the middle Pt layer. Our characterization results demonstrate that the best configuration can have absorption over 0.9 covering a wavelength span of 400 nm–1490 nm with a BW that is 1.8 times broader compared to that of planar design. On the other side, the proposed structure retains its absorption high at angles as wide as 70°. The results presented here can serve as a beacon for future performance enhanced multilayer designs where a simple fabrication step can boost the overall device response without changing its overall thickness and fabrication simplicity.
- Published
- 2017
36. Ultra-broadband Asymmetric Light Transmission and Absorption Through The Use of Metal Free Multilayer Capped Dielectric Microsphere Resonator
- Author
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Bayram Butun, Sina Abedini Dereshgi, Ekmel Ozbay, Amir Ghobadi, and Özbay, Ekmel
- Subjects
Materials science ,Fabrication ,Transfer-matrix method (optics) ,lcsh:Medicine ,chemistry.chemical_element ,02 engineering and technology ,Dielectric ,01 natural sciences ,Article ,010309 optics ,Resonator ,Stack (abstract data type) ,0103 physical sciences ,lcsh:Science ,Absorption (electromagnetic radiation) ,Multidisciplinary ,business.industry ,lcsh:R ,021001 nanoscience & nanotechnology ,chemistry ,Transmission (telecommunications) ,Optoelectronics ,lcsh:Q ,0210 nano-technology ,Tin ,business - Abstract
In this paper, we propose a simple design with an excellent performance to obtain high contrast in transmission asymmetry based on dielectric microspheres. Initially, we scrutinize the impact of the sphere radius on forward and backward transmissions. Afterward, by introducing a capping layer on top of the sphere, transmission response for the backward illuminated light will be blocked. In the next step, in order to replace the reflecting metal cap with a metal free absorbing design, we adopt a modeling approach based on the transfer matrix method (TMM) to explore an ideal material to achieve metal free perfect absorption in a multilayer configuration of material-insulator-material-insulator (MIMI). As a result of our investigations, it is found that Titanium Nitride (TiN) is an excellent alternative to replace metal in a MIMI multilayer stack. Setting this stack as the top capping coating, we obtain a high contrast between forward and backward light transmission where in an ultra-broadband range of 400 nm–1000 nm, forward transmission is above 0.85 while its backward response stays below 0.2. Moreover, due to the existence of multilayer stack, a high asymmetry is also observed for absorption profiles. This design has a relatively simple and large scale compatible fabrication route.
- Published
- 2017
37. Plasmonic enhanced terahertz time-domain spectroscopy system for identification of common explosives
- Author
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Bayram Butun, Ekmel Ozbay, and Yigit Demirag
- Subjects
Materials science ,010504 meteorology & atmospheric sciences ,Explosive material ,business.industry ,Terahertz radiation ,Terahertz ,Classification ,01 natural sciences ,Signal ,Constant false alarm rate ,010309 optics ,Algorithm ,Optics ,Transmission (telecommunications) ,Explosive ,0103 physical sciences ,Optoelectronics ,business ,Terahertz time-domain spectroscopy ,Spectroscopy ,Plasmon ,0105 earth and related environmental sciences - Abstract
Date of Conference:Proceedings of SPIE, Next-Generation Spectroscopic Technologies X Conference name: 10–11 April 2017 In this study, we present a classification algorithm for terahertz time-domain spectroscopy systems (THz-TDS) that can be trained to identify most commonly used explosives (C4, HMX, RDX, PETN, TNT, composition-B and blackpowder) and some non-explosive samples (lactose, sucrose, PABA). Our procedure can be used in any THz-TDS system that detects either transmission or reflection spectra at room conditions. After preprocessing the signal in low THz regime (0.1-3 THz), our algorithm takes advantages of a latent space transformation based on principle component analysis in order to classify explosives with low false alarm rate. © 2017 SPIE.
- Published
- 2017
38. Hybrid plasmon-phonon polariton bands in graphene-hexagonal boron nitride metamaterials [Invited]
- Author
-
Sina Abedini Dereshgi, Amir Ghobadi, Ekmel Ozbay, Bayram Butun, Hodjat Hajian, and Özbay, Ekmel
- Subjects
Plasmons ,Materials science ,Electromagnetic wave propagation ,Phonon ,Quantum emitters ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,Phonon polaritons ,law.invention ,Nitrides ,010309 optics ,Multi-layered graphene ,chemistry.chemical_compound ,Negative refraction ,law ,0103 physical sciences ,Polariton ,Dispersion (waves) ,Electromagnetic wave polarization ,Reststrahlen band ,Negative refractions ,Hexagonal boron nitride (h-BN) ,Plasmon ,Photons ,Graphene ,business.industry ,Metamaterial ,Statistical and Nonlinear Physics ,021001 nanoscience & nanotechnology ,Surface plasmon polaritons ,Surface plasmon polariton ,Atomic and Molecular Physics, and Optics ,Hexagonal boron nitride ,Boron nitride ,Refraction ,chemistry ,Metamaterials ,Quantum theory ,Light transmission ,Optoelectronics ,Phonons ,0210 nano-technology ,business - Abstract
We theoretically investigate mid-infrared electromagnetic wave propagation in multilayered graphene-hexagonal boron nitride (hBN) metamaterials. Hexagonal boron nitride is a natural hyperbolic material that supports highly dispersive phonon polariton modes in two Reststrahlen bands with different types of hyperbolicity. Due to the hybridization of surface plasmon polaritons of graphene and hyperbolic phonon polaritons of hBN, each isolated unit cell of the graphene-hBN metamaterial supports hybrid plasmon-phonon polaritons (HPPs). Through the investigation of band structure of the metamaterial we find that, due to the coupling between the HPPs supported by each unit cell, the graphene-hBN metamaterial can support HPP bands. The dispersion of these bands can be noticeably modified for different thicknesses of hBN layers, leading to the appearance of bands with considerably flat dispersions. Moreover, analysis of light transmission through the metamaterial reveals that this system is capable of supporting high-k propagating HPPs. This characteristic makes graphene-hBN metamaterials very promising candidates for the modification of the spontaneous emission of a quantum emitter, hyperlensing, negative refraction, and waveguiding. © 2017 Optical Society of America.
- Published
- 2017
39. 97 Percent Light Absorption In An Ultrabroadband Frequency Range Utilizing An Ultrathin Metal Layer: Randomly Oriented, Densely Packed Dielectric Nanowires As An Excellent Light Trapping Scaffold
- Author
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Hodjat Hajian, Gizem Birant, Alpan Bek, Bayram Butun, Ekmel Ozbay, Sina Abedini Dereshgi, Amir Ghobadi, and Özbay, Ekmel
- Subjects
Materials science ,Ultrathin metal layers ,Nanowire ,Transverse resonance mode ,Localized surface plasmon ,02 engineering and technology ,Dielectric ,Trapping ,01 natural sciences ,7. Clean energy ,Nanowire structures ,Dielectric materials ,010309 optics ,Atomic layer deposited ,Atomic layer deposition ,Optics ,0103 physical sciences ,General Materials Science ,Electromagnetic wave absorption ,Light absorption ,Platinum ,High-κ dielectric ,Scaffolds ,Different geometry ,Nanowires ,business.industry ,Titanium dioxides (TiO2) ,Resonance ,021001 nanoscience & nanotechnology ,Metals ,Titanium dioxide ,Dielectric nanowires ,Optoelectronics ,Titanium compounds ,0210 nano-technology ,business ,Layer (electronics) ,High-k dielectric - Abstract
In this paper, we propose a facile and large scale compatible design to obtain perfect ultrabroadband light absorption using metal-dielectric core-shell nanowires. The design consists of atomic layer deposited (ALD) Pt metal uniformly wrapped around hydrothermally grown titanium dioxide (TiO2) nanowires. It is found that the randomly oriented dense TiO2 nanowires can impose excellent light trapping properties where the existence of an ultrathin Pt layer (with a thickness of 10 nm) can absorb the light in an ultrabroadband frequency range with an amount near unity. Throughout this study, we first investigate the formation of resonant modes in the metallic nanowires. Our findings prove that a nanowire structure can support multiple longitudinal localized surface plasmons (LSPs) along its axis together with transverse resonance modes. Our investigations showed that the spectral position of these resonance peaks can be tuned with the length, radius, and orientation of the nanowire. Therefore, TiO2 random nanowires can contain all of these features simultaneously in which the superposition of responses for these different geometries leads to a flat perfect light absorption. The obtained results demonstrate that taking unique advantages of the ALD method, together with excellent light trapping of chemically synthesized nanowires, a perfect, bifacial, wide angle, and large scale compatible absorber can be made where an excellent performance is achieved while using less materials.
- Published
- 2017
40. Effect of gate structures on the DC and RF performance of AlGaN/GaN HEMTs
- Author
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Mustafa Kemal Öztürk, Sadan Ozcan, Omer Cengiz, Ahmet Toprak, Dogan Yilmaz, Ekmel Ozbay, Ozlem Sen, Sinan Osmanoglu, Bayram Butun, Özbay, Ekmel, Toprak, Ahmet, Osmanoǧlu, Sinan, Öztürk, Mustafa, Yılmaz, Doğan, and Bütün, Bayram
- Subjects
Frequency response ,Materials science ,Passivation ,Transconductance ,Recessed gate ,02 engineering and technology ,High-electron-mobility transistor ,High-electron mobility transistor (HEMT) ,01 natural sciences ,GaN ,law.invention ,law ,0103 physical sciences ,Materials Chemistry ,Electrical and Electronic Engineering ,010302 applied physics ,Field plate ,business.industry ,Gamma gate ,Transistor ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Cutoff frequency ,Electronic, Optical and Magnetic Materials ,AlGaN ,Optoelectronics ,Radio frequency ,0210 nano-technology ,business ,Voltage - Abstract
This work analyzes the effect of various gate structures on the DC and radio frequency (RF) performance of AlGaN/GaN high-electron mobility transistors (HEMTs). AlGaN/GaN HEMT devices with a 3 μm drain-to-source spacing, 125 μm gate width and 0.3 μm gate length in various gate structures were fabricated to achieve the desired frequency response with a robust, high yield, and repeatable process. The maximum drain current (IDS,max), maximum DC transconductance (gm), pinch-off voltage (Vth), current-gain cutoff frequency (fT), maximum oscillation frequency (fmax), and RF characteristics of the devices in terms of the small-signal gain and RF output power (Pout) at 8 GHz were investigated. The results showed that the output power is increased by 1 dB when the gate structure is changed from field plate to gamma gate. The Vth, gm, fT and fmax values are maximized when the thickness of the passivation layer between the gate foot and the gate head is minimized. It is shown that the IDS,max is decreased and Pout is increased when the gate recess etching process is performed.
- Published
- 2018
41. Planar indium tin oxide heater for improved thermal distribution for metal oxide micromachined gas sensors
- Author
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M. Çakır, Ekmel Ozbay, Bayram Butun, Deniz Caliskan, and Özbay, Ekmel
- Subjects
Materials science ,Oxide ,Analytical chemistry ,02 engineering and technology ,Metal oxide gas sensor ,lcsh:Chemical technology ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Temperature measurement ,Article ,Analytical Chemistry ,law.invention ,chemistry.chemical_compound ,Operating temperature ,law ,lcsh:TP1-1185 ,Electrical and Electronic Engineering ,Instrumentation ,Micro hot-plate ,Indium tin oxide ,SnO2 ,Heat distribution ,business.industry ,Heating element ,021001 nanoscience & nanotechnology ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Surface micromachining ,chemistry ,Optoelectronics ,Distribution uniformity ,Resistor ,0210 nano-technology ,business - Abstract
Metal oxide gas sensors with integrated micro-hotplate structures are widely used in the industry and they are still being investigated and developed. Metal oxide gas sensors have the advantage of being sensitive to a wide range of organic and inorganic volatile compounds, although they lack selectivity. To introduce selectivity, the operating temperature of a single sensor is swept, and the measurements are fed to a discriminating algorithm. The efficiency of those data processing methods strongly depends on temperature uniformity across the active area of the sensor. To achieve this, hot plate structures with complex resistor geometries have been designed and additional heat-spreading structures have been introduced. In this work we designed and fabricated a metal oxide gas sensor integrated with a simple square planar indium tin oxide (ITO) heating element, by using conventional micromachining and thin-film deposition techniques. Power consumption-dependent surface temperature measurements were performed. A 420 °C working temperature was achieved at 120 mW power consumption. Temperature distribution uniformity was measured and a 17 °C difference between the hottest and the coldest points of the sensor at an operating temperature of 290 °C was achieved. Transient heat-up and cool-down cycle durations are measured as 40 ms and 20 ms, respectively. © 2016 by the authors; licensee MDPI, Basel, Switzerland.
- Published
- 2016
42. Tuning the metal filling fraction in metal-insulator-metal ultra-broadband perfect absorbers to maximize the absorption bandwidth
- Author
-
Alireza R. Rashed, Bayram Butun, Ekmel Ozbay, Amir Ghobadi, Hodjat Hajian, Ghobadi, Amir, Hajian, Hodjat, Rashed, Alireza Rahimi, Bütün, Bayram, and Özbay, Ekmel
- Subjects
Fabrication ,Materials science ,business.industry ,Annealing (metallurgy) ,02 engineering and technology ,Metal-insulator-metal ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,010309 optics ,Wavelength ,Planar ,0103 physical sciences ,Optoelectronics ,0210 nano-technology ,Absorption (electromagnetic radiation) ,business ,Electron-beam lithography ,Matrix method - Abstract
In this paper, we propose a methodology to maximize the absorption bandwidth of a metal-insulator-metal (MIM) based absorber. The proposed structure is made of a Cr-Al2O3-Cr multilayer design. At the initial step, the optimum MIM planar design is fabricated and optically characterized. The results show absorption above 0.9 from 400 nm to 850 nm. Afterward, the transfer matrix method is used to find the optimal condition for the perfect light absorption in an ultra-broadband frequency range. This modeling approach predicts that changing the filling fraction of the top Cr layer can extend light absorption toward longer wavelengths. We experimentally proved that the use of proper top Cr thickness and annealing temperature leads to a nearly perfect light absorption from 400 nm to 1150 nm, which is much broader than that of a planar design. Therefore, while keeping the overall process lithography-free, the absorption functionality of the design can be significantly improved. The results presented here can serve as a beacon for future performance-enhanced multilayer designs where a simple fabrication step can boost the overall device response without changing its overall thickness and fabrication simplicity. (c) 2018 Chinese Laser Press
- Published
- 2018
43. Nearly perfect resonant absorption and coherent thermal emission by hBN-based photonic crystals
- Author
-
Bayram Butun, Hodjat Hajian, Amir Ghobadi, Ekmel Ozbay, and Özbay, Ekmel
- Subjects
Thermal emission ,Materials science ,Phonon ,Multilayer films ,Optical characteristics ,Physics::Optics ,Surface plasmons ,02 engineering and technology ,One-dimensional photonic crystal (1D PC) ,01 natural sciences ,Absorption ,010309 optics ,Photonic crystals ,Condensed Matter::Materials Science ,Planar ,Optics ,Microcomputers ,Polarization ,0103 physical sciences ,Coherent thermal emission ,Thin film ,Hexagonal boron nitride (h-BN) ,Lithography ,Photonic crystal ,business.industry ,Surface plasmon ,Potassium compounds ,Surface waves ,Surface plasmon polaritons ,021001 nanoscience & nanotechnology ,Surface plasmon polariton ,Atomic and Molecular Physics, and Optics ,Alternating layers ,Resonant absorption ,Multilayers ,Multilayer designs ,Optoelectronics ,Photonics ,0210 nano-technology ,business ,Optimized structures - Abstract
In this paper, we numerically demonstrate mid-IR nearly perfect resonant absorption and coherent thermal emission for both polarizations and wide angular region using multilayer designs of unpatterned films of hexagonal boron nitride (hBN). In these optimized structures, the films of hBN are transferred onto a Ge spacer layer on top of a one-dimensional photonic crystal (1D PC) composed of alternating layers of KBr and Ge. According to the perfect agreements between our analytical and numerical results, we discover that the mentioned optical characteristic of the hBN-based 1D PCs is due to a strong coupling between localized photonic modes supported by the PC and the phononic modes of hBN films. These coupled modes are referred as Tamm phonons. Moreover, our findings prove that the resonant absorptions can be red-or blue-shifted by changing the thickness of hBN and the spacer layer. The obtained results in this paper are beneficial for designing coherent thermal sources, light absorbers, and sensors operating within 6.2 mu m to 7.3 mu m in a wide angular range and both polarizations. The planar and lithography free nature of this multilayer design is a prominent factor that makes it a large scale compatible design. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
- Published
- 2017
44. Spectral response modification of TiO2 MSM photodetector with an LSPR filter
- Author
-
Bayram Butun, Deniz Caliskan, Sadan Ozcan, Ekmel Ozbay, and Özbay, Ekmel
- Subjects
Materials science ,Absorption spectroscopy ,Photodetector ,medicine.disease_cause ,Peak responsivity ,Filter structures ,FDTD simulations ,Responsivity ,Optics ,Surface plasmon resonance ,medicine ,Plasmon ,Photons ,business.industry ,Photodetectors ,Nanocylinders ,Resonance ,Localized surface plasmon resonance ,Atomic and Molecular Physics, and Optics ,MSM photodetector ,Optoelectronics ,Titanium dioxide ,Spectral response ,business ,Ultraviolet ,Plasmonic filters ,Visible spectrum - Abstract
We fabricated UVB filtered TiO2 MSM photodetectors by the localized surface plasmon resonance effect. A plasmonic filter structure was designed using FDTD simulations. Final filter structure was fabricated with Al nano-cylinders with a 70 nm radius 180 nm period on 360 nm SiO2 film. The spectral response of the TiO2 MSM photodetector was modified and the UVB response was reduced by approx. 60% with an LSPR structure, resulting in a peak responsivity shift of more than 40 nm. To our knowledge, this is the first published result for the spectral response modification of TiO2 photodetectors with LSPR technique. (C) 2014 Optical Society of America
- Published
- 2014
45. Low Dark Current And High Speed Zno Metal-Semiconductor-Metal Photodetector On Sio2/Si Substrate
- Author
-
Bayram Butun, Deniz Caliskan, Sadan Ozcan, Ekmel Ozbay, M. Cihan Çakır, and Özbay, Ekmel
- Subjects
Thin-film ,Fast Photoresponse ,Photocurrent ,Metal semiconductor metal photodetector ,Photoluminescence ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,High Speed ,Ultraviolet Detectors ,Photodetector ,Sputter deposition ,Responsivity ,Optics ,ZnO ,Optoelectronics ,Thin film ,business ,Current density ,Dark current - Abstract
ZnO thin films are deposited by radio-frequency magnetron sputtering on thermally grown SiO2 on Si substrates. Pt/Au contacts are fabricated by standard photolithography and lift-off in order to form a metal-semiconductor-metal (MSM) photodetector. The dark current of the photodetector is measured as 1 pA at 100V bias, corresponding to 100 pA/cm(2) current density. Spectral photoresponse measurement showed the usual spectral behavior and 0.35 A/W responsivity at a 100V bias. The rise and fall times for the photocurrent are measured as 22 ps and 8 ns, respectively, which are the lowest values to date. Scanning electron microscope image shows high aspect ratio and dense grains indicating high surface area. Low dark current density and high speed response are attributed to high number of recombination centers due to film morphology, deducing from photoluminescence measurements. These results show that as deposited ZnO thin film MSM photodetectors can be used for the applications needed for low light level detection and fast operation. (C) 2014 AIP Publishing LLC.
- Published
- 2014
46. Fano Resonances In Thz Metamaterials Composed Of Continuous Metallic Wires And Split Ring Resonators
- Author
-
Xiaodong Yang, Christina Daskalaki, Bayram Butun, Stylianos Tzortzakis, Ekmel Ozbay, Zhaofeng Li, Semih Cakmakyapan, and Özbay, Ekmel
- Subjects
Light ,Electromagnetically induced transparency ,Optical resonators ,Oscillators (mechanical) ,Refractive index ,Extraordinary optical transmission ,Fano plane ,Slow light ,Plasmonic Nanostructures ,Resonance ,Nanocircuits ,Split-ring resonator ,Clusters ,Group refractive index ,Nanocavities ,Optics ,Mathematics::Algebraic Geometry ,Split ring resonator ,Transmission curve ,Effective parameters ,Wire ,Capacitance change ,Transmission ,Symmetry-breaking ,Coupled oscillators ,Ring gages ,Physics ,Condensed matter physics ,business.industry ,Analog ,Fano resonance ,Metamaterial ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Atomic and Molecular Physics, and Optics ,Electric lines ,Lumped element model ,Metamaterials ,Modes ,Transmission spectrums ,business ,Theoretical modeling ,Electromagnetically Induced Transparency - Abstract
We demonstrate theoretically and experimentally that Fano resonances can be obtained in terahertz metamaterials that are composed of periodic continuous metallic wires dressed with periodic split ring resonators. An asymmetric Fano lineshape has been found in a narrow frequency range of the transmission curve. By using a transmission line combined with lumped element model, we are able to not only fit the transmission spectra of Fano resonance which is attributed to the coupling and interference between the transmission continuum of continuous metallic wires and the bright resonant mode of split ring resonators, but also reveal the capacitance change of the split ring resonators induced frequency shift of the Fano resonance. Therefore, the proposed theoretical model shows more capabilities than conventional coupled oscillator model in the design of Fano structures. The effective parameters of group refractive index of the Fano structure are retrieved, and a large group index more than 800 is obtained at the Fano resonance, which could be used for slow light devices. (C) 2014 Optical Society of America
- Published
- 2014
47. Silicon nanowire network metal-semiconductor-metal photodetectors
- Author
-
Mete Gunoven, Rasit Turan, Emre Mulazimoglu, Husnu Emrah Unalan, Sahin Coskun, Ekmel Ozbay, Bayram Butun, and Özbay, Ekmel
- Subjects
Silicon ,Fabrication ,Materials science ,Physics and Astronomy (miscellaneous) ,Performance ,On/off ratio ,Nanowire ,chemistry.chemical_element ,Photodetector ,Fabrication and characterizations ,Bending ,Si nanowires ,Metal ,Silicon nanowires ,Solution-processed ,Fast dynamic response ,Orientation ,Nanowire networks ,Transmittance ,Aqueous Fluoride Solution ,Arrays ,Metal semiconductor metal photodetector ,Photons ,Nanowires ,business.industry ,Solar-cells ,Room-temperature ,Photodetectors ,Dynamic response ,chemistry ,visual_art ,Electrode ,visual_art.visual_art_medium ,Optoelectronics ,Photovoltaic applications ,Flexible photodetectors ,Mechanism ,business - Abstract
We report on the fabrication and characterization of solution-processed, highly flexible, silicon nanowire network based metal-semiconductor-metal photodetectors. Both the active part of the device and the electrodes are made of nanowire networks that provide both flexibility and transparency. Fabricated photodetectors showed a fast dynamic response, 0.43 ms for the rise and 0.58 ms for the fall-time, with a decent on/off ratio of 20. The effect of nanowire-density on transmittance and light on/off behavior were both investigated. Flexible photodetectors, on the other hand, were fabricated on polyethyleneterephthalate substrates and showed similar photodetector characteristics upon bending down to a radius of 1 cm. (C) 2013 AIP Publishing LLC.
- Published
- 2013
48. InGaAs-based high-performance p-i-n photodiodes
- Author
-
Selim Unlu, Necmi Biyikli, I. Kimukin, Bayram Butun, Orhan Aytür, Ekmel Ozbay, Özbay, Ekmel, and Bıyıklı, Necmi
- Subjects
Materials science ,Passivation ,Photocurrents ,Bandwidth-efficiency ,Photodetector ,Optical power ,Deconvolution ,P-i-n Photodiode ,law.invention ,Gallium arsenide ,chemistry.chemical_compound ,Bandwidth ,Optics ,law ,P-i-n Photodiode, Photodetector ,Electrical and Electronic Engineering ,Microwaves ,Quantum Efficiency ,Photodiodes ,Bandwidth-effciency ,Photocurrent ,Resonant Cavity Enhanced ,business.industry ,High Speed ,Cavity Resonators ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Photodiode ,Semiconducting Indium Gallium Arsenide ,chemistry ,Optoelectronics ,Quantum efficiency ,business - Abstract
Cataloged from PDF version of article. In this letter, we have designed, fabricated, and characterized high-speed and high-efficiency InGaAs-based p-i-n photodetectors with a resonant cavity enhanced structure. The devices were fabricated by a microwave-compatible process. By using a postprocess recess etch, we tuned the resonance wavelength from 1605 to 1558 nm while keeping the peak efficiencies above 60%. The maximum quantum efficiency was 66% at 1572 nm which was in good agreement with our theoretical calculations. The photodiode had a linear response up to 6-mW optical power, where we obtained 5-mA photocurrent at 3-V reverse bias. The photodetector had a temporal response of 16 ps at 7-V bias. After system response deconvolution, the 3-dB bandwidth of the device was 31 GHz, which corresponds to a bandwidth-efficiency product of 20 GHz.
- Published
- 2002
49. High-performance visible-blind GaN-based p-i-n photodetectors
- Author
-
Bayram Butun, Turgut Tut, Ekmel Ozbay, Erkin Ulker, Tolga Yelboga, and Özbay, Ekmel
- Subjects
Low-noise ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Wide-bandgap semiconductor ,Photodetector ,Detectors ,Chemical vapor deposition ,Avalanche photodiode ,Avalanche Photodiodes ,Wavelength ,Responsivity ,Low Dark Current ,Sapphire ,Optoelectronics ,High Detectivity ,Schottky Photodiodes ,business ,Chemical-vapor-deposition ,Dark current - Abstract
Cataloged from PDF version of article. We report high performance visible-blind GaN-based p-i-n photodetectors grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The dark current of the 200 mu m diameter devices was measured to be lower than 20 pA for bias voltages up to 5 V. The breakdown voltages were higher than 120 V. The responsivity of the photodetectors was similar to 0.23 A/W at 356 nm under 5 V bias. The ultraviolet-visible rejection ratio was 6.7x10(3) for wavelengths longer than 400 nm. (C) 2008 American Institute of Physics.
- Published
- 2008
50. High performance AlxGa1-xN-based avalanche photodiodes
- Author
-
Turgut Tut, Ekmel Ozbay, Mutlu Gokkavas, Bayram Butun, and Özbay, Ekmel
- Subjects
Materials science ,Avalanche diode ,business.industry ,Nanophotonics ,Photodetector ,Schottky diode ,Schottky ,Condensed Matter Physics ,Avalanche photodiode ,Solar-blind ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Optics ,Single-photon avalanche diode ,Hardware and Architecture ,AlGaN ,Optoelectronics ,Wafer ,Avalanche ,Electrical and Electronic Engineering ,business ,Dark current - Abstract
We report high performance solar-blind photodetectors with reproducible avalanche gain as high as 820 under ultraviolet illumination. The solar-blind photodetectors have a sharp cut-off around 276 nm. We improved the device performance by designing different epitaxial wafer structure with thinner active multiplication layer. We compare the resulting fabricated devices from these wafers in terms of dark current, photoresponse, avalanche gain performances.
- Published
- 2007
Catalog
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