Browsing by Subject "InGaN"
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Item Open Access Absorption enhancement in InGaN-based photonic crystal-implemented solar cells(SPIE, 2012-07-26) Gundogdu, T. F.; Gokkavas, M.; Özbay, EkmelWe investigate the absorption characteristics of InGaN solar cells with high indium (0.8) content and a one-dimensional periodic nano-scale pattern (implemented) in the InGaN layer theoretically. The short-circuit current of our InGaN-based solar cell structure is calculated for different lattice constant, etch depth, and fill factor values. A substantial increase in the absorption (17.5% increase in short-circuit current) is achieved when the photonic crystal pattern is thoroughly optimized. (c) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JNP.6.061603]Item Open Access Blue InGaN/GaN-based quantum electroabsorption modulators(IEEE, 2006) Sarı, Emre; Nizamoğlu, Sedat.; Özel, Tuncay; Demir, Hilmi VolkanWe introduce InGaN/GaN-based quantum electroabsorption modulator that incorporates ∼5 nm thick In0.35Ga0.65N/GaN quantum structures for operation in the blue spectral range of 420-430 nm. This device exhibits an optical absorption coefficient change of ∼6000 cm-1 below the band edge at highly transmissive, blue region (at λ peak=424 nm) with a 6 V swing and emits blue light (at λpeak=440 nm) with an optical output power of 0.35 mW at a 20 mA current injection level. Unlike infrared III-V quantum modulators, this blue modulator shows a blue shift in its electroabsorption (for λ < 418 nm) with increasing applied field accross it, due to high alternating polarization fields in its quantum structures; this electroabsorption behavior is opposite to the conventional quantum confined Stark effect that features common red shift. This device holds great promise for > 10 GHz optical clock injection directly into silicon CMOS chips in the blue because of its low parasitic in-series resistance (< 100 Ω) and the possibility to make smaller device mesas for low capacitance (1.2 fF for a 10μm×10μm mesa size). Considering high-speed operation and high responsivity of silicon-on-insulator (SOI) photodetectors in the blue range, unlike in the infrared, this approach eliminates the need for on-chip hybrid integration of Si CMOS with III-V photodetectors. Furthermore, the efficient electroluminescence of this device makes it feasible to consider on-chip blue laser-modulator integration for a compact optical clocking scheme. © 2006 IEEE.Item Open Access Determination of the band gap of indium-rich InGaN by means of photoacoustic spectroscopy(Institute of Physics Publishing, 2018) Oliva, R.; Zelewski, S. J.; Janicki, L.; Gwóźdź, K. R.; Serafińczuk, J.; Rudziński, M.; Özbay, Ekmel; Kudrawiec, R.Photoacoustic (PA) measurements have been performed on a series of InxGa1-xN thin films grown with x > 50%. In order to illustrate the usefulness of this technique, these measurements have been compared with the results obtained by the following conventional techniques: photoluminescence, transmittance and contactless electroreflectance. Amongst all these techniques, only PA spectroscopy exhibited signal without the undesired Fabry-Perot interferences arising from the thin film and buffer layer. By accurately assessing the strain state and composition of our samples, we were able to study the compositional dependence of the band gap of our epilayers. Our results show that a bowing parameter of 1.43 eV successfully describes the compositional dependence of the band gap of InGaN.Item Open Access Determination of the critical indium composition corresponding to the metal-insulator transition in InxGa1-xN (0.06 ≤ x ≤ 0.135) layers(Elsevier, 2009-10-13) Yildiz, A.; Lisesivdin, S. B.; Tasli, P.; Özbay, Ekmel; Kasap, M.The low-temperature conductivity of InxGa1-xN alloys (0.06 ≤ x ≤ 0.135) is analyzed as a function of indium composition (x). Although our InxGa1-xN alloys were on the metallic side of the metal-insulator transition, neither the Kubo-Greenwood nor Born approach were able to describe the transport properties of the InxGa1-xN alloys. In addition, all of the InxGa1-xN alloys took place below the Ioeffe-Regel regime with their low conductivities. The observed behavior is discussed in the framework of the scaling theory. With decreasing indium composition, a decrease in thermal activation energy is observed. For the metal-insulator transition, the critical indium composition is obtained as xc = 0.0543 for InxGa1-xN alloys.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 Examination of the temperature related structural defects of InGaN/GaN solar cells(Academic Press, 2015) Durukan, İ. K.; Bayal, Ö.; Kurtuluş, G.; Baş, Y.; Gültekin, A.; Öztürk, M. K.; Çörekçi, S.; Tamer, M.; Özçelik, S.; Özbay, EkmelIn this study the effects of the annealing temperature on the InGaN/GaN solar cells with different In-contents grown on sapphire substrate by the Metal Organic Chemical Vapor Deposition (MOCVD) are analyzed by High Resolution X-ray Diffraction (HRXRD) and an Atomic Force Microscope (AFM). The plane angles, mosaic crystal sizes, mixed stress, dislocation intensities of the structure of the GaN and InGaN layers are determined. According to the test results, there are no general characteristic trends observed due to temperature at both structures. There are fluctuating failures determined at both structures as of 350 °C. The defect density increased on the GaN layer starting from 350 °C and reaching above 400 °C. A similar trend is observed on the InGaN layer, too.Item Open Access Forward tunneling current in Pt/p-InGaN and Pt/n-InGaN Schottky barriers in a wide temperature range(Elsevier, 2012-07-27) Arslan, E.; Çakmak, H.; Özbay, EkmelThe current-transport mechanisms of the Pt contacts on p-InGaN and n-InGaN were investigated in a wide temperature range (80-360 K) and in the forward bias regime. It was found that the ideality factor (n) values and Schottky barrier heights (SBHs), as determined by thermionic emission (TE), were a strong function of temperature and Φb0 show the unusual behavior of increasing linearly with an increase in temperature from 80 to 360 K for both Schottky contacts. The tunneling saturation ( JTU(0)) and tunneling parameters (E 0) were calculated for both Schottky contacts. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. The results indicate that the dominant mechanism of the charge transport across the Pt/p-InGaN and Pt/n-InGaN Schottky contacts are electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-360 K.Item Open Access InGaN green light emitting diodes with deposited nanoparticles(Elsevier BV, 2007) Butun, B.; Cesario J.; Enoch, S.; Quidant, R.; Özbay, EkmelWe grew an InGaN/GaN-based light-emitting diode (LED) wafer by metal-organic chemical vapor deposition (MOCVD), fabricated devices by optical lithography, and successfully deposited ellipsoidal Ag nano-particles by way of e-beam lithography on top. The diodes exhibited good device performance, in which we expected an enhancement of the radiated intensity by the simulations and emission measurements. The obtained results showed the feasibility of plasmon-assisted LED emission enhancement.Item Open Access Numerical optimization of In-mole fractions and layer thicknesses in AlxGa1-xN/AlN/GaN high electron mobility transistors with InGaN back barriers(ELSEVIER, 2011-02-01) Kelekci, O.; Lisesivdin, S. B.; Ozcelik, S.; Özbay, EkmelThe effects of the In-mole fraction (x) of an InxGa 1-xN back barrier layer and the thicknesses of different layers in pseudomorphic AlyGa1-yN/AlN/GaN/InxGa 1-xN/GaN heterostructures on band structures and carrier densities were investigated with the help of one-dimensional self-consistent solutions of non-linear SchrdingerPoisson equations. Strain relaxation limits were also calculated for the investigated AlyGa1-yN barrier layer and InxGa1-xN back barriers. From an experimental point of view, two different optimized structures are suggested, and the possible effects on carrier density and mobility are discussed.