Browsing by Subject "Indium"
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Item Open Access The effect of growth conditions on the optical and structural properties of InGaN/GaN MQW LED structures grown by MOCVD(Gazi University Eti Mahallesi, 2014) Cetđn, S.; Sağlam, S.; Ozcelđk, S.; Özbay, EkmelFive period InGaN/GaN MQW LED wafers were grown by low pressure MOCVD on an AlN buffer layer, which was deposited on a c-plane (0001)-faced sapphire substrate. The effect of growth conditions, such as the well growth time, growth temperatures, and indium flow rate on the properties of MQW structures were investigated by using high resolution X-ray diffraction and room temperature photoluminescence. By increasing growth temperature, the emission wavelengths showed a blue-shift while it red-shifted via an increase in the indium flow rate. The emission wavelength can be tuned by way of changing the well growth time of the samples. ©2014 Gazi University Eti Mahallesi. All rights reserved.Item Open Access Effect of reactor pressure on optical and electrical properties of InN films grown by high-pressure chemical vapor deposition(Wiley - V C H Verlag GmbH & Co. KGaA, 2015) Alevli, M.; Gungor, N.; Alkis, S.; Ozgit Akgun, C.; Donmez, I.; Okyay, Ali Kemal; Gamage, S.; Senevirathna, I.; Dietz, N.; Bıyıklı, NecmiThe influences of reactor pressure on the stoichiometry, free carrier concentration, IR and Hall determined mobility, effective optical band edge, and optical phonon modes of HPCVD grown InN films have been analysed and are reported. The In 3d, and N 1s XPS spectra results revealed In-N and N-In bonding states as well as small concentrations of In-O and N-O bonds, respectively in all samples. InN layers grown at 1 bar were found to contain metallic indium, suggesting that the incorporation of nitrogen into the InN crystal structure was not efficient. The free carrier concentrations, as determined by Hall measurements, were found to decrease with increasing reactor pressure from 1.61×1021 to 8.87×1019 cm-3 and the room-temperature Hall mobility increased with reactor pressure from 21.01 to 155.18 cm2/Vs at 1 and 15 bar reactor pressures, respectively. IR reflectance spectra of all three (1, 8, and 15 bar) InN samples were modelled assuming two distinct layers of InN, having different free carrier concentration, IR mobility, and effective dielectric function values, related to a nucleation/interfacial region at the InN/sapphire, followed by a bulk InN layer. The effective optical band gap has been found to decrease from 1.19 to 0.95 eV with increasing reactor pressure. Improvement of the local structural quality with increasing reactor pressure has been further confirmed by Raman spectroscopy measurements. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Open Access Electronic properties of polypyrrole/polyindene composite/metal junctions(Elsevier, 1997) Bozkurt, A.; Ercelebi, C.; Toppare, L.Junction properties between conducting polymer composites of polypyrrole/polyindene (PPy/PIn) with different conductivities and metals like Pt, Au, Al and In have been investigated. Rectifying junctions were observed for low work function metals, In and Al; however, high work function metals, Pt and Au, were observed to form ohmic contacts to PPy/PIn composite in the sandwich geometry. The rectifying behavior of the metal/composite/Pt junctions improved when the conductivity of the composite was decreased from 1 to 0.01 S/cm. Using the ideal Schottky theory various junction parameters have been determined. All planar junctions were ohmic regardless of the conductivities of the samples.Item Open Access Enhanced light scattering with energy downshifting using 16 nm indium nitride nanoparticles for improved thin-film a-Si N-i-P solar cells(Electrochemical Society Inc., 2015-05) Chowdhury F.I.; İslam, K.; Alkış, Sabri; Ortaç, Bülend; Alevli, Mustafa; Dietz, N.; Okyay, Ali Kemal; Nayfeh, A.In this work the effect of Indium nitride (InN) nanoparticles (NPs) on the performance of a-Si: H solar cells has been investigated. The average Jsc of InN NPs coated cells was found 6.76 mA/cm2 which is 16.69% higher than the average Jsc of the reference cell which was 5.79 mA/cm2. Average efficiency of InN NPs coated cells showed 14.16% increase from 3.32% to 3.79%. Peak EQE has increased from 44.8% at 500 nm to 51.67% at 510 nm and peak IQE has increased from 51.70% at 510 nm to 68.38% at 500 nm for InN NPs coated cell. Further study shows that EQE change is larger between 510 nm-700 nm compared to IQE change indicting a surface scattering mechanism that reduces the reflectivity. However, between 400 nm-510 nm IQE change is larger than EQE change which indicates that energy downshifting mechanism is dominating. So overall performance enhancement can be attributed to the scattering and photoluminescence properties of InN NPs that enhances absorption inside a-Si: H solar cells. © The Electrochemical Society.Item Open Access Fabrication and characterization of liquid metal-based micro-electromechanical DC-contact switch for RF applications(CRC Press, 2012) Çağatay, Engin; Noyan, Mehmet Alican; Damgaci, Y.; Cetiner, B. A.; Bıyıklı, NecmiWe demonstrate that room-temperature liquid metal alloy droplets of Eutectic Gallium Indium (EGaIn) and Gallium Indium Tin alloy (Galinstan) can be actuated using electro-wetting-on-dielectric (EWOD) effect. With the application of 80-100V across the actuation electrode and ground electrode, the metallic liquid droplets were observed to be actuated. We have studied the actuation characteristics using different electrode architectures in open-air configuration as well as in encapsulated microfluidic channel test-beds. The resulting microfluidic DC actuation might potentially be used for RF switching applications.Item Open Access Generation of InN nanocrystals in organic solution through laser ablation of high pressure chemical vapor deposition-grown InN thin film(Springer, 2012-07-27) Alkis, S.; Alevli, M.; Burzhuev, S.; Vural, H. A.; Okyay, Ali Kemal; Ortaç, B.We report the synthesis of colloidal InN nanocrystals (InN-NCs) in organic solution through nanosecond pulsed laser ablation of high pressure chemical vapor deposition-grown InN thin film on GaN/sapphire template substrate. The size, the structural, the optical, and the chemical characteristics of InN-NCs demonstrate that the colloidal InN crystalline nanostructures in ethanol are synthesized with spherical shape within 5.9-25.3, 5.45-34.8, 3.24-36 nm particle-size distributions, increasing the pulse energy value. The colloidal InN-NCs solutions present strong absorption edge tailoring from NIR region to UV region.Item Open Access Improved InGaN/GaN light-emitting diodes with a p-GaN/n-GaN/p-GaN/n-GaN/p-GaN current-spreading layer(Optical Society of American (OSA), 2013) Zhang, Z.-H.; Tan, S.T.; Liu W.; Ju, Z.; Zheng, K.; Kyaw, Z.; Ji, Y.; Hasanov, N.; Sun X.W.; Demir, Hilmi VolkanThis work reports both experimental and theoretical studies on the InGaN/GaN light-emitting diodes (LEDs) with optical output power and external quantum efficiency (EQE) levels substantially enhanced by incorporating p-GaN/n-GaN/p-GaN/n-GaN/p-GaN (PNPNP-GaN) current spreading layers in p-GaN. Each thin n-GaN layer sandwiched in the PNPNP-GaN structure is completely depleted due to the built-in electric field in the PNPNP-GaN junctions, and the ionized donors in these n-GaN layers serve as the hole spreaders. As a result, the electrical performance of the proposed device is improved and the optical output power and EQE are enhanced. © 2013 Optical Society of America.Item Open Access Indium rich InGaN solar cells grown by MOCVD(Springer New York LLC, 2014) Çakmak, H.; Arslan, E.; Rudziński, M.; Demirel, P.; Unalan, H. E.; Strupiński, W.; Turan, R.; Öztürk, M.; Özbay, EkmelThis study focuses on both epitaxial growths of InxGa 1-xN epilayers with graded In content, and the performance of solar cells structures grown on sapphire substrate by using metal organic chemical vapor deposition. The high resolution X-ray and Hall Effect characterization were carried out after epitaxial InGaN solar cell structures growth. The In content of the graded InGaN layer was calculated from the X-ray reciprocal space mapping measurements. Indium contents of the graded InGaN epilayers change from 8.8 to 7.1 % in Sample A, 15.7-7.1 % in Sample B, and 26.6-15.1 % in Sample C. The current voltage measurements of the solar cell devices were carried out after a standard micro fabrication procedure. Sample B exhibits better performance with a short-circuit current density of 6 mA/cm2, open-circuit voltage of 0.25 V, fill factor of 39.13 %, and the best efficiency measured under a standard solar simulator with one-sun air mass 1.5 global light sources (100 mW/cm2) at room temperature for finished devices was 0.66 %.Item Open Access Low-temperature grown wurtzite InxGa1−xN thin films via hollow cathode plasma-assisted atomic layer deposition(Royal Society of Chemistry, 2015-08) Haider A.; Kizir S.; Ozgit Akgun, C.; Goldenberg, E.; Leghari, S. A.; Okyay, Ali Kemal; Bıyıklı, NecmiHerein, we report on atomic layer deposition of ternary InxGa1−xN alloys with different indium contents using a remotely integrated hollow cathode plasma source. Depositions were carried out at 200 °C using organometallic Ga and In precursors along with N2/H2 and N2 plasma, respectively. The effect of In content on structural, optical, and morphological properties of InxGa1−xN thin films was investigated. Grazing incidence X-ray diffraction showed that all InxGa1−xN thin films were polycrystalline with a hexagonal wurtzite structure. X-ray photoelectron spectroscopy depicted the peaks of In, Ga, and N in bulk of the film and revealed the presence of relatively low impurity contents. In contents of different InxGa1−xN thin films were determined by energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Transmission electron microscopy also confirmed the polycrystalline structure of InxGa1−xN thin films, and elemental mapping further revealed the uniform distribution of In and Ga within the bulk of InxGa1−xN films. Higher In concentrations resulted in an increase of refractive indices of ternary alloys from 2.28 to 2.42 at a wavelength of 650 nm. The optical band edge of InxGa1−xN films red-shifted with increasing In content, confirming the tunability of the band edge with alloy composition. Photoluminescence measurements exhibited broad spectral features with an In concentration dependent wavelength shift and atomic force microscopy revealed low surface roughness of InxGa1−xN films with a slight increase proportional to In content.Item Open Access Low-temperature hollow cathode plasma-assisted atomic layer deposition of crystalline III-nitride thin films and nanostructures(Wiley - V C H Verlag GmbH & Co. KGaA, 2015) Ozgit Akgun, C.; Goldenberg, E.; Bolat, S.; Tekcan, B.; Kayaci, F.; Uyar, Tamer; Okyay, Ali Kemal; Bıyıklı, NecmiHollow cathode plasma-assisted atomic layer deposition (HCPA-ALD) is a promising technique for obtaining III-nitride thin films with low impurity concentrations at low temperatures. Here we report our previous and current efforts on the development of HCPA-ALD processes for III-nitrides together with the properties of resulting thin films and nanostructures. The content further includes nylon 6,6-GaN core-shell nanofibers, proof-of-concept thin film transistors and UV photodetectors fabricated using HCPA-ALD-grown GaN layers, as well as InN thin films deposited by HCPA-ALD using cyclopentadienyl indium and trimethylindium precursors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Open Access Low-temperature self-limiting atomic layer deposition of wurtzite InN on Si(100)(American Institute of Physics Inc., 2016) Haider, A.; Kizir, S.; Bıyıklı, NecmiIn this work, we report on self-limiting growth of InN thin films at substrate temperatures as low as 200 °C by hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD). The precursors used in growth experiments were trimethylindium (TMI) and N2 plasma. Process parameters including TMI pulse time, N2 plasma exposure time, purge time, and deposition temperature have been optimized for self-limiting growth of InN with in ALD window. With the increase in exposure time of N2 plasma from 40 s to 100 s at 200 °C, growth rate showed a significant decrease from 1.60 to 0.64 Å/cycle. At 200 °C, growth rate saturated as 0.64 Å/cycle for TMI dose starting from 0.07 s. Structural, optical, and morphological characterization of InN were carried out in detail. X-ray diffraction measurements revealed the hexagonal wurtzite crystalline structure of the grown InN films. Refractive index of the InN film deposited at 200 °C was found to be 2.66 at 650 nm. 48 nm-thick InN films exhibited relatively smooth surfaces with Rms surface roughness values of 0.98 nm, while the film density was extracted as 6.30 g/cm3. X-ray photoelectron spectroscopy (XPS) measurements depicted the peaks of indium, nitrogen, carbon, and oxygen on the film surface and quantitative information revealed that films are nearly stoichiometric with rather low impurity content. In3d and N1s high-resolution scans confirmed the presence of InN with peaks located at 443.5 and 396.8 eV, respectively. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) further confirmed the polycrystalline structure of InN thin films and elemental mapping revealed uniform distribution of indium and nitrogen along the scanned area of the InN film. Spectral absorption measurements exhibited an optical band edge around 1.9 eV. Our findings demonstrate that HCPA-ALD might be a promising technique to grow crystalline wurtzite InN thin films at low substrate temperatures.Item Open Access Plasmonics: merging photonics and electronics at nanoscale dimensions((AAAS) American Association for the Advancement of Science, 2006) Özbay, EkmelElectronic circuits provide us with the ability to control the transport and storage of electrons. However, the performance of electronic circuits is now becoming rather limited when digital information needs to be sent from one point to another. Photonics offers an effective solution to this problem by implementing optical communication systems based on optical fibers and photonic circuits. Unfortunately, the micrometer-scale bulky components of photonics have limited the integration of these components into electronic chips, which are now measured in nanometers. Surface plasmon-based circuits, which merge electronics and photonics at the nanoscale, may offer a solution to this size-compatibility problem. Here we review the current status and future prospects of plasmonics in various applications including plasmonic chips, light generation, and nanolithography.