Browsing by Subject "Heterostructure"

Now showing 1 - 8 of 8

Open Access
Design, fabrication and characterization of high-performance solarblind AlGaN photodetectors
(SPIE, 2005) Özbay, Ekmel
Design, fabrication, and characterization of high-performance AlxGal-xN-based photodetectors for solar-blind applications are reported. AlxGal-xN heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal (MSM) photodiodes. The resulting solar-blind AlGaN detectors exhibited low dark current, high detectivity, and high bandwidth.
Open Access
Design, synthesis and application of electrospun heterostructured nanofibers for electrocatalytic hydrogen evolution reactions from water splitting
(2021-11) Yılmaz, Elif Begüm
Environmental problems and climate changes have increased the importance of studies on the development of sustainable and clean energy methods that can be an alternative to energy production technologies using fossil fuels in recent years. Green hydrogen is environmentally friendly and a high-capacity energy carrier, as it does not cause any toxic by-products during its production. For this reason, attempts are being made to increase the efficiency of green hydrogen produced from water splitting. Development of the catalytic activities and stability of electrocatalysts has gained great importance in order to increase the performance of the hydrogen evolution reaction (HER). This study examines the effect of Ni/NiO-reduced graphene oxide catalysts fabricated in the form of heterostructured fibers by electrospinning on their intrinsic and extrinsic activities and their performance for HER. In order to examine the stability, activity and kinetics of the synthesized electrocatalyst, studies such as linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), were carried out and Tafel curves were interpreted. It has been observed that the optimal electrocatalyst exhibits outstanding electrocatalytic performance with an over potential of -212 mV at 10 mA cm-2, and a Tafel slope of 90.6 mV dec-1 in alkaline electrolyte. Morphological and structural characterizations of electrocatalysts were investigated using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM) methods.
Open Access
The effect of strain relaxation on electron transport in undoped Al0.25Ga0.75N/GaN heterostructures
(Elsevier BV * North-Holland, 2007-11-01) Lişesivdin, S. B.; Yıldız, A.; Acar, S.; Kasap, M.; Özçelik, S.; Özbay, Ekmel
The two-dimensional electron gas (2DEG) transport properties of two-step growth undoped Al0.25Ga0.75N/GaN heterostructures with semi-insulating buffer, grown by MOCVD, were investigated in a temperature range of 20–350 K. Using the quantitative mobility spectrum analysis (QMSA) method, it was shown that significant parallel conduction does not occur in worked structures. In-plain growth axis strains are calculated using the total polarization-induced charge density taken as the sheet carrier density measured from the Hall effect. It was found that the calculated strain values are in good agreement with those reported. Influences of the two-step growth parameters such as growth ramp time, the annealing temperature of the GaN nucleation layer on the mobility, and density of the 2DEG are also discussed.
Open Access
Effect of various pseudomorphic AIN layer insertions on the electron densities of two-dimensional electron gas in lattice-matched In0.18AI0.82N/GaN based heterostructures
(Institutul National de Cercetare-Dezvoltare pentru Optoelectronica, 2009) Lisesivdin, S. B.; Özbay, Ekmel
We explored the effects of various pseudomorphic AlN layer insertions in lattice-matched In0.18Al0.82N/GaN based heterostructures on band structures and carrier densities with the help of one-dimensional self-consistent solutions of non-linear Schrödinger-Poisson equations. According to the calculations, important increase in carrier density is expected with an increasing number of AlN insertions in In0.18Al0.82N barrier. The effect of the position of an AlN layer in In0.18Al0.82N barrier is also investigated. An additional AlN layer insertion in the GaN layer is calculated in detail with the help of an experimental point of view, in which the possible effects on both carrier density and mobility are discussed.
Open Access
High-performance AlxGA1-xN-Based UV photodetectors for visible/solar-blind applications
(2004) Bıyıklı, Necmi
High-performance detection of ultraviolet (UV) radiation is of great importance for a wide range of applications including flame sensing, environmental (ozone layer) monitoring, detection of biological/chemical agents, missile early warning systems, and secure intersatellite communication systems. These applications require high-performance UV photodetectors with low dark current, high responsivity, high detectivity, and fast time response. The widebandgap AlxGa1−xN ternary alloy is well-suited as a photodetector material for operation in the wavelength range of 200 nm to 365 nm. Its outstanding material properties (direct bandgap, tunable cut-off, allows heterostructures, intrinsically solar-blind) make AlxGa1−xN suitable for a variety of harsh environments. If properly constructed, AlxGa1−xN-based photodetectors could offer significant advantages over the older photomultiplier tube (PMT) technology in terms of size, cost, robustness, complexity, dark current, bandwidth, and solar-blind operation. The motivation behind this work is the need for high-performance, solid-state UV photodetectors that can be cost-effectively manufactured into high-density arrays. We have designed, fabricated, and characterized several visible/solar-blind AlxGa1−xN photodiode samples. With solar-blind AlxGa1−xN photodiode samples, we achieved excellent device performance in almost all aspects. Very low dark currents were measured with heterostructure AlxGa1−xN Schottky and p-i-n samples. The extremely low leakage characteristics resulted in record detectivity and noise performance. Detectivity performance comparable to PMT detectivity was achieved. True solar-blind operation (sub-280 nm cut-off) with high visible rejection was demonstrated. In addition, we improved the bandwidth performance of AlxGa1−xN-based solar-blind photodetectors by over an order of magnitude. Solar-blind Schottky, p-i-n, and metal-semiconductor-metal photodiode samples exhibited very fast pulse response with multi-GHz bandwidths.
Open Access
High-performance solar-blind AlGaN photodetectors
(SPIE, 2005) Özbay, Ekmel; Tut, Turgut; Bıyıklı, N.
Design, fabrication, and characterization of high-performance Al xGa1-xN-based photodetectors for solar-blind applications are reported. AlxGa1-xN heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3 fA leakage currents at 6 V and 12 V reverse bias were measured on p-i-n and Schottky photodiode samples respectively. The excellent current-voltage (I-V) characteristics led to a detectivity performance of 4.9×1014 cmHz1/2W-1. The MSM devices exhibited photoconductive gain, while Schottky and p-i-n samples displayed 0.15 A/W and 0.11 A/W peak responsivity values at 267 nm and 261 nm respectively. All samples displayed true solar-blind response with cut-off wavelengths smaller than 280 nm. A visible rejection of 4×104 was achieved with Schottky detector samples. High speed measurements at 267 nm resulted in fast pulse responses with >GHz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.
Open Access
ITO-schottky photodiodes for high-performance detection in the UV-IR spectrum
(IEEE, 2004) Bıyıklı, Necmi; Kimukin, I.; Butun, B.; Aytür, O.; Özbay, Ekmel
High-performance vertically illuminated Schottky photodiodes with indium-tin-oxide (ITO) Schottky layers were designed, fabricated, and tested. Ternary and quarternary III-V material systems (AlGaN-GaN, AlGaAs-GaAs, InAlGaAs-InP, and InGaAsP-InP) were utilized for detection in the ultraviolet (UV) (λ < 400 nm), near-IR (λ ∼ 850 nm), and IR (λ ∼ 1550 nm) spectrum. The material properties of thin ITO films were characterized. Using resonant-cavity-enhanced (RCE) detector structures, improved efficiency performance was achieved. Current-voltage, spectral responsivity, and high-speed measurements were carried out on the fabricated ITO-Schottky devices. The device performances obtained with different material systems are compared.
Open Access
Multilayer mXene heterostructures and nanohybrids for multifunctional applications: a review
(American Chemical Society, 2022-05-17) Tasnim Mahmud, S.; Bain, S; Hasan, Md Mehdi; Rahman, S.T.; Rhaman, M.; Hossain, M.M.; Ordu, Mustafa
MXenes (transition metal carbides and nitrides) have experienced exponential growth over the last two decades, thanks to their excellent physical, chemical, and mechanical properties. Intriguing properties like high conductivity, wear, and corrosion resistance while maintaining flexibility are the strong motivation behind the exploration of MXenes. Moreover, the large surface area and unique layered structure enhance the functionality of multilayer-MXene heterostructures and hybrids. This paper reviews the synthesis chemistry, structure properties of multilayer MXenes, and their multifunctional applications. MXene synthesis under different conditions, their hybrids and composites, intercalation, and structural geometries are discussed. The electrical, mechanical, optical, and magnetic properties of MXenes are briefly presented. Recent progress and development in MXene-based heterostructures and nanohybrids for supercapacitors, batteries, environmental and water treatment, antibacterial and tissue engineering, and electromagnetic absorption and shielding are systematically discussed. Finally, research challenges and a perspective in this specified area are addressed for potential developments.