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1
Habtemichael, Yishak Tekleab. "Packaging designs for ultraviolet light emitting diodes." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45764.
Full textAbstract:
Aluminum Gallium Nitride (AlGaN) / Gallium Nitride (GaN) based deep ultraviolet (DUV) light emitting didoes (LEDs) with emission wavelengths between 200-280 nm enable key emerging technologies such as water/air purification and sterilization, covert communications and portable bio-agent detection/identification systems for homeland security, and surface and medical device sterilization. These devices produce a large amount of undesired heat due to low quantum efficiencies in converting electrical input to optical output. These low efficiencies are attributed to difficulties in the growth&doping of AlₓGa₁₋ₓN materials and UV absorbing substrates leading to excessive joule heating, which leads to device degradation and a spectral shift in the emission wavelength. With this regard, effective thermal management in these devices depends on the removal of this heat and reduction of the junction temperature. This is achieved by decreasing the package thermal resistance from junction-to-air with cost-effective solutions. The use of heat sinks, thermal interface materials, and high conductivity heat spreaders is instrumental in the reduction of the overall junction-to-air thermal resistance.
This thesis work focuses on thermal modeling of flip-chip packaged deep UV LEDs to gain a better understanding of the heat propagation through these devices as well as the package parameters that have the biggest contributions to reducing the overall thermal resistance. A parametric study focusing on components of a lead frame package is presented to ascertain the thermal impacts of various package layers including contact metallizations, thermal spreading sub-mounts, and thermal interface materials. In addition the use of alternative thermal interface materials such as phase change materials and liquid metals is investigated experimentally.
2
Cheung, Yuk-fai, and 張煜輝. "Phosphor-free multilayered LEDs and thin film LEDs." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50900067.
Full textAbstract:
The irreversible trend of replacing the conventional incandescence light bulbs and fluorescent tubes with white light emitting diodes (LEDs) aims to use less energy for lighting. Plenty of the commercially available white LEDs are made from blue LED chips with few-micron-thick gallium nitride (GaN) grown on several hundred micron thick transparent sapphire substrates, followed by coating of yellow phosphor powder on top of the chips for converting the emitted blue light to white light. Not only does such approach give the white LEDs a high colour temperature, but also introduces conversion loss from the phosphor powder. The former issue makes users feel unpleasant for living while the latter wastes energy.
Therefore, a new version of phosphor-free multilayered vertically-stacked colour-tunable LED structure is proposed in this thesis such that it allows users to regulate the colour temperature of light source according to their preference. Simultaneously, the device replaces light conversion agents with direct light generation. The fabrication of the proposed device involved the use of backside laser micromachining of trenches on the substrates of the upper layers of basic colour LED chips at a size just enough to fit the wire-bonded wire of lower layer LED chips inside. With equal-sized basic colour LED chips tightly packed together, colour homogeneity of the proposed device is enhanced and thus provides the proposed device the capability to substitute the conventional RGB LED devices with basic colour LED chips separately aligned.
To improve the internal quantum efficiency and light extraction of nitride-based LEDs, thin film photonic crystal LED is proposed. Light and heat trapping sapphire substrate is removed by laser lift-off (LLO), forming GaN thin film on an electrically conductive opaque substrate with better heat conductivity than sapphire. By proper etching, N-dopped GaN layer can be exposed, resulting in the formation of vertical LED. Compared with conventional lateral LEDs with sapphire substrate, carrier path of vertical LED is greatly reduced and hence achieving lower internal resistance. To further boost light extraction, the device top surface is patterned with nanopillars by nanosphere lithography. A monolayer of closely-packed silica nanospheres is patterned on the N-GaN surface by spin coating. It acts as a mask for etching the nanopillars which bandfold lights from diffracted modes to radiative modes located above the light line for extraction.
A typical laser LLO process results in thin films with undopped gallium nitride (U-GaN) surface or N-GaN (after etching) faces up. If P-side up is necessary, the GaN layers are first required to attach to a temporary substrate for LLO and then the LLO exposed surface is adhered to the real substrate before temporary substrate is detached. This method is proposed to relieve the issue of light channeling inside the sapphire substrate of full colour LED micro-display panel fabricated on a single GaN on Sapphire wafer. With the elimination of sapphire, “parasitic” blue emissions from the area surrounding pixels are reduced which in turns improved the observable effects from the microspheres jet-printed on the top surface of the panel.published_or_final_version
Electrical and Electronic Engineering
Master
Master of Philosophy
3
Bergenek, Krister. "Thin-film photonic crystal LEDs with enhanced directionality." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/912.
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Liang, Hu. "Fabrication and characteristics of the InGaN/GaN multiple quantum well blue LEDs /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202003%20LIANG.
Full textAbstract:
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 62-66). Also available in electronic version. Access restricted to campus users.
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Snyman, LW, H. Aharoni, and Plessis M. du. "A dependency of quantum efficiency of silicon CMOS n+pp+ LEDs on current density." IEEE Photonics Technology Letters, 2005. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001057.
Full textAbstract:
Abstract—A dependency of quantum efficiency of nn+pp+ silicon
complementary metal–oxide–semiconductor integrated lightemitting
devices on the current density through the active device
areas is demonstrated. It was observed that an increase in current
density from 1 6 10+2 to 2 2 10+4 A cm 2 through the active
regions of silicon n+pp+ light-emitting diodes results in an increase
in the external quantum efficiency from 1 6 10 7 to 5 8
10 6 (approximately two orders of magnitude). The light intensity
correspondingly increase from 10 6 to 10 1 W cm 2 mA (approximately
five orders of magnitude). In our study, the highest
efficiency device operate in the p-n junction reverse bias avalanche
mode and utilize current density increase by means of vertical and
lateral electrical field confinement at a wedge-shaped n+ tip placed
in a region of lower doping density and opposite highly conductive
p+ regions.
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Qin, Yaxiao. "High Efficiency SEPIC Converter For High Brightness Light Emitting Diodes (LEDs) System." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/44422.
Full textAbstract:
This thesis presents an investigation into the characteristics of and driving methods for light emitting diode (LED) lamp system. A comprehensive overview on the lighting development is proposed. The characteristic of the light emitting diode (LED) lamp is described and the requirements of the ballast for the light emitting diode (LED) lamp are presented.
Although LED lamps have longer lifetime than fluorescent lamps, the short lifetime limitation of LED driver imposed by electrolytic capacitor has to be resolved. Therefore, an LED driver without electrolytic capacitor in the whole power conversion process is preferred. In this thesis, a single phase, power factor correction converter without electrolytic capacitors for LED lighting applications is proposed, which is a modified SEPIC converter working in discontinuous conduction mode (DCM). Different with a conventional SEPIC converter, the middle capacitor is replaced with a valley-fill circuit. The valley-fill circuit could reduce the voltage stress of output diode and middle capacitor under the same power factor condition, thus achieving higher efficiency. Instead of using an electrolytic capacitor for the filter, a polyester capacitor of better lifetime expectancy is used.
An interleaved power factor correction SEPIC with valley fill circuit is proposed to further increase the efficiency and to reduce the input and output filter size and cost. The interleaved converter shows the features such as ripple cancellation, good thermal distribution and scalability.Master of Science
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Stone, Roni. "An investigation into novel red emitting phosphors and their applications." Thesis, Brunel University, 2011. http://bura.brunel.ac.uk/handle/2438/6296.
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New red emitting phosphors, based on the double tungstate/molybdates, were discovered. Some were able to retain their luminous efficacy after substituting Y3+ for Eu3+, reducing the cost of the phosphor. This substitution was attempted for existing commercial red emitting phosphors and proved unsuccessful. Another set of phosphors based on these lattices were discovered and the emitted luminous efficacy was 140% greater than other reported Eu3+ phosphors. The best of these was Na2WO4MoO4Eu0.44Al1.34Sm0.011. The integration of phosphors to the lighting application was also studied, including improvements in light extraction for existing phosphors. ACEL panels are currently applied to many applications and were briefly examined. The more recent OLED technology was investigated and comparisons can be drawn with the ACEL panels. LEDs were also a focus of the work with a new method developed for remote application of phosphors to LEDs, based on a dome shaped encapsulant, and this was adopted commercially by a high brightness LED manufacturer. The studies on the phosphors reported herein were aimed at integrating these into commercial applications. Although this was not achieved as brightness and particles size were problematic, if it is demonstrated that further development of the synthetic methods produce phosphors with suitable attributes, this may lead to the integration in applications.
8
Pinos, Andrea. "Optical properties and degradation of deep ultraviolet AIGaN-based light-emitting diodes." Doctoral thesis, KTH, Fotonik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-37917.
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Bano, Nargis. "Fabrication and Characterization of ZnO Nanorods Based Intrinsic White Light Emitting Diodes (LEDs)." Doctoral thesis, Linköpings universitet, Fysik och elektroteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-71829.
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ZnO material based hetero-junctions are a potential candidate for the design andrealization of intrinsic white light emitting devices (WLEDs) due to several advantages overthe nitride based material system. During the last few years the lack of a reliable andreproducible p-type doping in ZnO material with sufficiently high conductivity and carrierconcentration has initiated an alternative approach to grow n-ZnO nanorods (NRs) on other ptypeinorganic and organic substrates. This thesis deals with ZnO NRs-hetero-junctions basedintrinsic WLEDs grown on p-SiC, n-SiC and p-type polymers. The NRs were grown by thelow temperature aqueous chemical growth (ACG) and the high temperature vapor liquid solid(VLS) method. The structural, electrical and optical properties of these WLEDs wereinvestigated and analyzed by means of scanning electron microscope (SEM), current voltage(I-V), photoluminescence (PL), cathodoluminescence (CL), electroluminescence (EL) anddeep level transient spectroscopy (DLTS). Room temperature (RT) PL spectra of ZnOtypically exhibit one sharp UV peak and possibly one or two broad deep level emissions(DLE) due to deep level defects in the bandgap. For obtaining detailed information about thephysical origin, growth dependence of optically active defects and their spatial distribution,especially to study the re-absorption of the UV in hetero-junction WLEDs structure depthresolved CL spectroscopy, is performed. At room temperature the CL intensity of the DLEband is increased with the increase of the electron beam penetration depth due to the increaseof the defect concentration at the ZnO NRs/substrate interface. The intensity ratio of the DLEto the UV emission, which is very useful in exploring the origin of the deep level emissionand the distribution of the recombination centers, is monitored. It was found that the deepcenters are distributed exponentially along the ZnO NRs and that there are more deep defectsat the root of ZnO NRs compared to the upper part. The RT-EL spectra of WLEDs illustrateemission band covering the whole visible range from 420 nm and up to 800 nm. The whitelightcomponents are distinguished using a Gaussian function and the components were foundto be violet, blue, green, orange and red emission lines. The origin of these emission lines wasfurther identified. Color coordinates measurement of the WLEDs reveals that the emitted lighthas a white impression. The color rendering index (CRI) and the correlated color temperature(CCT) of the fabricated WLEDs were calculated to be 80-92 and 3300-4200 K, respectively.
10
Potfajova, Jaroslava. "Silicon based microcavity enhanced light emitting diodes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-25451.
Full textAbstract:
Realising Si-based electrically driven light emitters in a process technology compatible with mainstream microelectronics CMOS technology is key requirement for the implementation of low-cost Si-based optoelectronics and thus one of the big challenges of semiconductor technology. This work has focused on the development of microcavity enhanced silicon LEDs (MCLEDs), including their design, fabrication, and experimental as well as theoretical analysis. As a light emitting layer the abrupt pn-junction of a Si diode was used, which was fabricated by ion implantation of boron into n-type silicon. Such forward biased pn-junctions exhibit room-temperature EL at a wavelength of 1138 nm with a reasonably high power efficiency of 0.1%. Two MCLEDs emitting light at the resonant wavelength about 1150 nm were demonstrated: a) 1-lambda MCLED with the
resonator formed by 90 nm thin metallic CoSi2 mirror at the bottom and semitransparent distributed Bragg reflector (DBR) on the top; b) 5.5-lambda MCLED with the resonator formed by high reflecting DBR at the bottom and semitransparent top DBR. Using the appoach of the 5.5-lambda MCLED with two DBRs the extraction efficiency is enhanced by about 65% compared to the silicon bulk pn-junction diode.
11
Alvi, Naveed ul Hassan. "Luminescence Properties of ZnO Nanostructures and Their Implementation as White Light Emitting Diodes (LEDs)." Doctoral thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-69155.
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In this thesis, luminescence properties of ZnO nanostructures (nanorods, nanotubes, nanowalls and nanoflowers) are investigated by different approaches for possible future application of these nanostructures as white light emitting diodes. ZnO nanostructures were grown by different growth techniques on different p-type substrates. Still it is a challenge for the researchers to produce a stable and reproducible high quality p-type ZnO and this seriously hinders the progress of ZnO homojunction LEDs. Therefore the excellent properties of ZnO can be utilized by constructing heterojunction with other p-type materials. The first part of the thesis includes paper I-IV. In this part, the luminescence properties of ZnO nanorods grown on different p-type substrates (GaN, 4H-SiC) and different ZnO nanostructures (nanorods, nanotubes, nanoflowers, and nanowalls) grown on the same substrate were investigated. The effect of the post-growth annealing of ZnO nanorods and nanotubes on the deep level emissions and color rendering properties were also investigated. In paper I, ZnO nanorods were grown on p-type GaN and 4H-SiC substrates by low temperature aqueous chemical growth (ACG) method. The luminescence properties of the fabricated LEDs were investigated at room temperature by electroluminescence (EL) and photoluminescence (PL) measurements and consistency was found between both the measurements. The LEDs showed very bright emission that was a combination of three emission peaks in the violet-blue, green and orange-red regions in the visible spectrum. In paper II, different ZnO nanostructures (nanorods, nanotubes, nanoflowers, and nanowalls) were grown on p-GaN and the luminescence properties of these nanostructures based LEDs were comparatively investigated by EL and PL measurements. The nanowalls structures were found to be emitting the highest emission in the visible region, while the nanorods have the highest emissions in the UV region due to its good crystal quality. It was also estimated that the ZnO nanowalls structures have strong white light with the highest color rendering index (CRI) of 95 with correlated color temperature (CCT) of 6518 K. In paper III, we have investigated the origin of the red emissions in ZnO by using post-growth annealing. The ZnO nanotubes were achieved on p-GaN and then annealed in different ambients (argon, air, oxygen and nitrogen) at 600 oC for 30 min. By comparative investigations of EL spectra of the LEDs it was found that more than one deep level defects are involved in the red emission from ZnO nanotubes/p-GaN LEDs. It was concluded that the red emission in ZnO can be attributed to oxygen interstitials (Oi) and oxygen vacancies (Vo) in the range of 620 nm (1.99 eV) to 690 nm (1.79 eV) and 690 nm (1.79 eV) to 750 nm (1.65 eV), respectively. In paper IV, we have investigated the effect of post-growth annealing on the color rendering properties of ZnO nanorods based LEDs. ZnO nanorods were grown on p-GaN by using ACG method. The as grown nanorods were annealed in nitrogen, oxygen, argon, and air ambients at 600 oC for 30 min. The color rendering indices (CRIs) and correlated color temperatures (CCTs) were estimated from the spectra emitted by the LEDs. It was found that the annealing ambients especially air, oxygen, and nitrogen were found to be very effective. The LEDs based on nanorods annealed in nitrogen ambient, have excellent color rendering properties with CRIs and CCTs of 97 and 2363 K in the forward bias and 98 and 3157 K in the reverse bias. In the 2nd part of the thesis, the junction temperature of n-ZnO nanorods based LEDs at the built-in potential was modeled and experiments were performed to validate the model. The LEDs were fabricated by ZnO nanorods grown on different p-type substrates (4H-SiC, GaN, and Si) by the ACG method. The model and experimental values of the temperature coefficient of the forward voltage near the built-in potential (~Vo) were compared. It was found that the series resistance has the main contribution in the junction temperature of the fabricated devices. In the 3rd part of the thesis, the influence of helium (He+) ion irradiation bombardment on luminescence properties of ZnO nanorods based LEDs were investigated. ZnO nanorods were grown by the vapor-liquid-solid (VLS) growth method. The fabricated LEDs were irradiated by using 2 MeV He+ ions with fluencies of ~ 2×1013 ions/cm2 and ~ 4×1013 ions/cm2. It was observed that the He+ ions irradiation affects the near band edge emissions as well as the deep level emissions in ZnO. A blue shift about 0.0347 eV and 0.082 eV was observed in the PL spectra in the near band emission and green emission, respectively. EL measurements also showed a blue shift of 0.125 eV in the broad green emission after irradiation. He+ ion irradiation affects the color rendering properties and decreases the color rendering indices from 92 to 89.
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Schwalb, Michael. "Measuring the short term plant photosynthetic response to varying light quality using light emitting diodes (LEDs)." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121207.
Full textAbstract:
Light emitting diodes (LEDs) emit narrow bandwidth light and have the potential to increase the spectral efficiency of supplemental lighting in greenhouses by optimizing spectral output for plant growth and yields. At the moment of writing, data describing the plant response to varying light quality and quantity was limited. The objective of this research was to examine photosynthetic response of plants to varying light quality and quantity and to gather photosynthetic response data that could be used to design an optimal spectrum for a prototype LED array for plant growth experiments. The action spectrum of tomato (Solanum lycopersicum), lettuce (Lactuca sativa) and petunia (Petunia × hybrida) seedlings was measured at three irradiances (30, 60 and 120 µmol m-2 sec-1) using LED arrays with peak wavelengths from 405nm – 700nm and a bandwidth of 25nm (full width at half maximum). The action spectrums for all plant species at all three irradiances were characterized by localized blue and red action peaks within the range of 430 to 449 nm and 624 to 660 nm respectively. A peak also occurred at 595 nm for 30 µmol m-2 sec-1. The photosynthetic response of tomato, lettuce and petunia to varying red (660nm) and blue (430nm) wavelengths with and without background broadband radiation was also measured. For all three species tested, with and without background radiation, the optimum photosynthesis range occurred within the red to blue ratio (r:b) range of 5:1- 15:1 except for petunia without background radiation for which the maximum occurred at 50:1. These results suggest that the optimal red to blue ratio for photosynthetic activity for tomato, lettuce and petunia occurred between a red to blue ratio of 5:1-15:1.Les diodes électroluminescentes (DEL) émettent une lumière relativement monochromatique et pourraient accroître l'efficacité des lampes pour les serres commerciales en émettant des longueurs d'ondes optimisées pour le rendement des plantes. L'objectif de ce projet a consisté à examiner l'effet des longueurs d'ondes sur l'activité photosynthétique des plantes. L'activité photosynthétique des tomates (Solanum lycopersicum), laitues (Lactuca sativa) et pétunias (Petunia × hybrida) a été mesurée à trois puissances d'irradiation (30, 60 and 120 µmol m-2 sec-1) en utilisant des DELs avec une émission maximale entre 405 nm et 700 nm et une bande passante de 25 nm. La réponse photosynthétique maximale à chaque niveau d'irradiation se situait dans la portion bleu et rouge du spectre visible, soit respectivement entre 430 - 449 nm et 624 to 660 nm. Un maximum a aussi été observé à 595 nm à 30 µmol m-2 sec-1. L'effet de la proportion des longueurs d'onde bleue et rouge (émises par les DELs) sur l'activité photosynthétique des tomates, laitues et pétunias a aussi été mesuré avec et sans le rayonnement de fond. Pour chaque espèce, avec et sans le rayonnement de fond, la proportion optimale (en terme de rouge et bleu) pour l'activité photosynthétique se situait entre of 5:1- 15:1, sauf dans le cas du pétunia, pour lequel le maximum se situait à 50:1 sans rayonnement de fond. La proportion optimale pour l'activité photosynthétique a diminué avec le rayonnement de fond pour chaque espèce à chaque niveau d'irradiation.
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Potfajova, J. "Silicon based microcavity enhanced light emitting diodes." Forschungszentrum Dresden-Rossendorf, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-27756.
Full textAbstract:
Realising Si-based electrically driven light emitters in a process technology compatible with mainstream microelectronics CMOS technology is key requirement for the implementation of low-cost Si-based optoelectronics and thus one of the big challenges of semiconductor technology. This work has focused on the development of microcavity enhanced silicon LEDs (MCLEDs), including their design, fabrication, and experimental as well as theoretical analysis. As a light emitting layer the abrupt pn-junction of a Si-diode was used, which was fabricated by ion implantation of boron into n-type silicon. Such forward biased pn-junctions exhibit room-temperature EL at a wavelength of 1138 nm with a reasonably high power efficiency of 0.1% [1]. Two MCLEDs emitting light at the resonant wavelength about 1150 nm were demonstrated: a) 1 MCLED with the resonator formed by 90 nm thin metallic CoSi2 mirror at the bottom and semitranparent distributed Bragg reflector (DBR) on the top; b) 5:5 MCLED with the resonator formed by high reflecting DBR at the bottom and semitransparent top DBR. Using the appoach of the 5:5 MCLED with two DBRs the extraction efficiency is enhanced by about 65% compared to the silicon bulk pn-junction diode.
14
Liang, Hu. "Fabrication of high power InGaN/GaN multiple quantum well blue LEDs grown on patterned Si substrates /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?ECED%202008%20LIANG.
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Potfajova, J. "Silicon based microcavity enhanced light emitting diodes." Forschungszentrum Dresden-Rossendorf, 2009. https://hzdr.qucosa.de/id/qucosa%3A21604.
Full textAbstract:
Realising Si-based electrically driven light emitters in a process technology compatible with mainstream microelectronics CMOS technology is key requirement for the implementation of low-cost Si-based optoelectronics and thus one of the big challenges of semiconductor technology. This work has focused on the development of microcavity enhanced silicon LEDs (MCLEDs), including their design, fabrication, and experimental as well as theoretical analysis. As a light emitting layer the abrupt pn-junction of a Si-diode was used, which was fabricated by ion implantation of boron into n-type silicon. Such forward biased pn-junctions exhibit room-temperature EL at a wavelength of 1138 nm with a reasonably high power efficiency of 0.1% [1]. Two MCLEDs emitting light at the resonant wavelength about 1150 nm were demonstrated: a) 1 MCLED with the resonator formed by 90 nm thin metallic CoSi2 mirror at the bottom and semitranparent distributed Bragg reflector (DBR) on the top; b) 5:5 MCLED with the resonator formed by high reflecting DBR at the bottom and semitransparent top DBR. Using the appoach of the 5:5 MCLED with two DBRs the extraction efficiency is enhanced by about 65% compared to the silicon bulk pn-junction diode.:List of Abbreviations and Symbols
1 Introduction and motivation
2 Theory
2.1 Electronic band structure of semiconductors
2.2 Light emitting diodes (LED)
2.2.1 History of LED
2.2.2 Mechanisms of light emission
2.2.3 Electrical properties of LED
2.2.4 LED e ciency
2.3 Si based light emitters
2.4 Microcavity enhanced light emitting pn-diode
2.4.1 Bragg reflectors
2.4.2 Fabry-Perot resonators
2.4.3 Optical mode density and emission enhancement in coplanar Fabry-Perot resonator
2.4.4 Design and optical properties of a Si microcavity LED
3 Preparation and characterisation methods
3.1 Preparation techniques
3.1.1 Thermal oxidation of silicon
3.1.2 Photolithography
3.1.3 Wet chemical cleaning and etching
3.1.4 Ion implantation
3.1.5 Plasma Enhanced Chemical Vapour Deposition (PECVD) of silicon nitride
3.1.6 Magnetron sputter deposition
3.2 Characterization techniques
3.2.1 Variable Angle Spectroscopic Ellipsometry (VASE)
3.2.2 Fourier Transform Infrared Spectroscopy (FTIR)
3.2.3 Microscopy
3.2.4 Electroluminescence and photoluminescence measurements
4 Experiments, results and discussion
4.1 Used substrates
4.1.1 Silicon substrates
4.1.2 Silicon-On-Insulator (SOI) substrates
4.2 Fabrication and characterization of distributed Bragg reflectors
4.2.1 Deposition and characterization of SiO2
4.2.2 Deposition of Si
4.2.3 Distributed Bragg Reflectors (DBR)
4.2.4 Conclusions
4.3 Design of Si pn-junction LED
4.4 Resonant microcavity LED with CoSi2 bottom mirror
4.4.1 Device preparation
4.4.2 Electrical Si diode characteristics
4.4.3 EL spectra
4.4.4 Conclusions
4.5 Si based microcavity LED with two DBRs
4.5.1 Test device
4.5.2 Device fabrication
4.5.3 LED on SOI versus MCLED
4.5.4 Conclusions
5 Summary and outlook
5.1 Summary
5.2 Outlook
A Appendix
A.1 The parametrization of optical constants
A.1.1 Kramers-Kronig relations
A.1.2 Forouhi-Bloomer dispersion formula
A.1.3 Tauc-Lorentz dispersion formula
A.1.4 Sellmeier dispersion formula
A.2 Wafer holder
List of publications
Acknowledgements
Declaration / Versicherung
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Fernandes, Ricardo Liz de Castilho. "Green emitting diodes for solid state lighting." Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/17763.
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Mestrado em Engenharia FísicaNos anos recentes a iluminação de estado sólido impulsionou alternativas de iluminação efí cientes e ecológicas. Os desafi os correntes envolvem o desenvolvimento de materiais emissores de luz que convertem radiação de uma determinada energia para radiação de energia mais baixa, na gama do visível. Esta tese estuda um complexo novo, Tb(NaI)3(H2O)2 onde NaI é o ácido nalidíxico, que emite na região do verde e é estável sob iluminação no ultravioleta. Este foi incorporado em materiais híbridos orgânico-inorgânico tripodais com dois pesos moleculares médios (3000 e 5000 g.mol-1, denominados t- U(3000) e t-U(5000) respetivamente) que permitem o processamento de monólitos e fi lmes com forma e espessura controlada. Estes híbridos também aumentam o rendimento quântico absoluto de emissão de 0.11 medidos para o Tb(NaI)3(H2O)2 isolado para ~0.82 após incorporação no t-U(5000). Foi também demonstrado o potencial de usar estes materiais híbridos como emissores na região verde para uso em iluminação de estado sólido através do revestimento do díodo emissor na região ultravioleta (365 nm). Este LED apresenta uma efi cácia de 1.3 lm.W1.
In the last few years, solid state light-emitting diodes (LEDs) have been driving the lighting industry towards energy e cient and environmental friendly lighting. Current challenges encompass e cient and low-cost downconverting photoluminescent phosphors with emission in the visible region. This thesis will cover a novel UV-photostable green emitting complex, Tb(NaI)3(H2O)2 where NaI is nalidixic acid, was incorporated into organic-inorganic tripodal hybrid materials with two average molecular weights (3000 and 5000 g.mol{1, termed as t- U(5000) and t-U(3000), respectively) which enable the easy shaping of monoliths and lms with controlled thickness. Moreover, the hybrid hosts boost the Tb3+ green absolute emission quantum yield from 0.11 measured for the isolated Tb(NaI)3(H2O)2 complex to 0.82 after incorporation into t-U(5000). The potential use of the hybrid materials as UV-down converting green-emitting phosphors for solid state lighting was demonstrated by means of coating a near-UV LED (365 nm). This LED shows an e cacy of 1.3 lm.W1.
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Lam, N. D., S. Kim, J. J. Lee, K. R. Choi, M. H. Doan, and H. Lim. "Enhanced Luminescence of InGaN / GaN Vertical Light Emitting Diodes with an InGaN Protection Layer." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35210.
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We have investigated the effectiveness of a thin n-In0.2Ga0.8N layer inserted in the bottom n-GaN layer
of InGaN/GaN blue light emitting diodes (LEDs) for the protection of multiple quantum wells during the
laser lift-off process for vertical LED fabrication. The photoluminescence properties of the InGaN/GaN
lateral LEDs are nearly identical irrespective of the existence of the n-In0.2Ga0.8N insertion layer in the
bottom n-GaN layer. However, such an insertion is found to effectively increase the photoluminescence
intensity of the multiple quantum well and the carrier lifetime of the vertical LEDs. These improvements
are attributed to the reduced defect generations in the vertical LEDs during the laser lift-off process due to
the presence of the protection layer.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35210
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Greenham, Neil Clement. "Electroluminescence in conjugated polymers." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296643.
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Anutgan, Mustafa. "Nanocrystal Silicon Based Visible Light Emitting Pin Diodes." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612718/index.pdf.
Full textAbstract:
The production of low cost, large area display systems requires a light emitting material
compatible with the standard silicon (Si) based complementary metal oxide semiconductor
(CMOS) technology. The crystalline bulk Si is an indirect band semiconductor with very
poor optical properties. On the other hand, hydrogenated amorphous Si (a-Si:H) based wide
gap alloys exhibit strong visible photoluminescence (PL) at room temperature, owing to the
release of the momentum conservation law. Still, the electroluminescence (EL) intensity from
the diodes based on these alloys is weak due to the limitation of the current transport by the
localized states.
In the frame of this work, first, the luminescent properties of amorphous silicon nitride
(a-SiNx:H) thin films grown in a plasma enhanced chemical vapor deposition (PECVD) system
were analyzed with respect to the nitrogen content. Then, the doping effciency of p- and
n-type hydrogenated nanocrystalline Si (nc-Si:H) films was optimized via adjusting the deposition
conditions. Next, the junction quality of these doped layers was checked and further
improved in a homojunction pin diode.
Heterojunction pin light emitting diodes (LEDs) were fabricated with a-SiNx:H as the
luminescent active layer. The EL effciency of the fresh diodes was very low, as expected.
As a solution, the diodes were electro-formed under high electric field leading to nanocrystallization
accompanied by a strong visible light emission from the whole diode area. The
current-voltage (I-V) and EL properties of these transformed diodes were investigated in detail.
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Guan, Nan. "Nitride nanowire light-emitting diode." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS372/document.
Full textAbstract:
Les nanofils nitrures présentent des propriétés optoélectroniques extraordinaires et sont considérés comme des matériaux prometteurs pour des diodes électroluminescentes (LEDs), grâce à leur haute qualité cristalline, leurs surfaces non-polaires, leur bonne flexibilité mécanique, leur rapport d’aspect élevé, etc.Cette thèse adresse la croissance, la fabrication, les caractérisations optiques et électriques et la simulation optique des dispositifs à base de nanofils nitrures, avec un accent particulier sur les LEDs à nanofils.Premièrement, cette thèse présente la croissance par épitaxie en phase vapeur aux organométalliques de nanofils nitrures cœur-coquille auto-assemblés contenant des puits quantiques InGaN/GaN sur les facettes plan m avec différentes concentrations d’In. Puis est décrite la fabrication de LEDs utilisant ces nanofils suivant deux différentes stratégies d’intégration (intégrations planaires et verticales).L’intégration planaire est basée sur des nanofils uniques dispersés horizontalement. J’ai proposé une plateforme photonique intégrée composée d’une LED à nanofil, d’un guide d’onde optimisé et d’un photodétecteur à nanofil. J’ai également développé un système d’alignement des nanofils.L’intégration verticale a pour objectif la réalisation de LEDs flexibles reposant sur une assemblée de nanofils verticaux encapsulées dans des polymères. Je montre que ceci permet la fabrication de LEDs flexibles monochromatiques, bi-couleurs ou blanches.Les nanofils épitaxiés sur des matériaux 2D par épitaxie de van de Waals sont faciles à décoller de leur substrat natif. Avec cette motivation, dans la dernière partie de cette thèse, j’ai étudié la croissance organisée des nanofils GaN sur du graphène micro et nano-structuré utilisant l’épitaxie par jets moléculairesNitride nanowires exhibit outstanding opto-electronic and mechanical properties and are considered as promising materials for light-emitting diodes (LEDs), thanks to their high crystalline quality, non-polar facets, good mechanical flexibility, high aspect ratio, etc.This Ph.D. thesis addresses the growth, the device fabrication, the optical and electrical characterizations and the optical simulations of III-nitride NW devices, with a special emphasis on the LED applications.First, this thesis presents the growth of m-plane InGaN/GaN quantum wells with different In concentrations in self-assembled core-shell nanowires by metal-organic chemical vapor deposition. Then, by using these nanowires, LED devices based on two different integration strategies (namely, in-plane and vertical integration) are demonstrated.The in-plane integration is based on the horizontally dispersed single nanowires. I have proposed a basic integrated photonic platform consisting of a nanowire LED, an optimized waveguide and a nanowire photodetector. I have also developed a nanowire alignment system using dielectrophoresis.The vertical integration targets the fabrication of flexible LEDs based on vertical nanowire arrays embedded in polymer membranes. Flexible monochromatic, bi-color, white LEDs have been demonstrated. Their thermal properties have been analyzed.The nanowires grown on 2D materials by van der Waals epitaxy are easy to be lifted-off from their native substrate, which should facilitate the fabrication of flexible nanowire devices. With this motivation, in the last part of this thesis, I have investigated the selective area growth of GaN NWs on micro- and nano- scale graphene by molecular beam epitaxy
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Lochner, Zachary Meyer. "Green light emitting diodes and laser diodes grown by metalorganic chemical vapor deposition." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33827.
Full textAbstract:
This thesis describes the development of III-Nitride materials for light emitting applications. The goals of this research were to create and optimize a green light emitting diode (LED) and laser diode (LD). Metalorganic chemical vapor deposition (MOCVD) was the technique used to grow the epitaxial structures for these devices.
The active regions of III-Nitride based LEDs are composed of InₓGa₁₋ₓN, the bandgap of which can be tuned to attain the desired wavelength depending on the percent composition of Indium. An issue with this design is that the optimal growth temperature of InGaN is lower than that of GaN, making the growth temperature of the top p-layers critical to the device performance. Thus, an InGaN:Mg layer was used as the hole injection and p-contact layers for a green led, which can be grown at a lower temperature than GaN:Mg in order to maintain the integrity of the active region. However, the use of InGaN comes with its own set of drawbacks, specifically the formation of V-defects. Several methods were investigated to suppress these defects such as graded p-layers, short period supper lattices, and native GaN substrates. As a result, LEDs emitting at ~532 nm were realized.
The epitaxial structure for a III-Nitride LD is more complicated than that of an LED, and so it faces many of the same technical challenges and then some. Strain engineering and defect reduction were the primary focuses of optimization in this study. Superlattice based cladding layers, native GaN substrates, InGaN waveguides, and doping optimization were all utilized to lower the probability of defect formation. This thesis reports on the realization of a 454 nm LD, with higher wavelength devices to follow the same developmental path.
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Li, Sinan, and 李思南. "Several reliability issues and solutions for LED lighting system." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/197552.
Full textAbstract:
This thesis presents a study on several reliability issues for LED lighting systems. Firstly, a full survey on exsiting LED ballast has been conducted, and critical design challenges are classified on power level basis (low/ middle/ high power). Specifically, reliability issues have been highlighted, and three major factors have been stipulated: issue of electrolytic capacitor; issue of current imbalance in parallel LED strings; issue of LED junction temperature. The information revealed in the whole survey provide important design criteria for existing LED system designs and guidance for further research directions by pointing out the critical design problems.
Two possible solutions for Electrolytic-Capacitor-Less LED Ballasts are proposed regarding the first reliability issue. A series of novel passive LED ballasts are proposed. They are found to be suitable for outdoor applications, such as street lighting applications, where the ability to withstand extreme weather conditions are of major concern. When compared with those in switched mode power supplies, these passive ballasts have good power factor performance and comparatively high efficiency. In addition, an active solution has been developed for indoor applications. Its circuit topology is derived from existing differential inverter topologies and inherits same merits such as simple structure, reduced size, and low cost.
Self-configurable current-mirror techniques have been derived and developed afterwards to cope with the current imbalance issue for system with parallel LED strings. In contrast with traditional current sharing methods (either linear type or switched type), the proposed techniques offer a simple solution without the need of independent current references, complicated controllers and auxiliary power supplies. These features are favored by outdoor applications and such re-configurable mirror circuits are originally designed for passive LED ballast as post-current regulators. The techniques are further extended with the ability to tolerate possible circuit failure, such as short circuit and open circuit fault.
Then, a new non-contact method for the measurement of both junction-to-case thermal resistance and junction temperature in a LED device has been proposed, with respect to the third reliability issue. Traditionally the direct measurement of junction temperature in LED is not easy without the help of sophisticated methods such as laser or expensive equipment like TeraLED Transient Thermal Tester system. In contrast, the proposed method requires only the external LED power, luminous flux, and heatsink temperature information. The method can be further adopted as a simple tool by engineers to check the internal temperature states in a practical LED system for regulation and evaluation purpose.
Finally, a thermal design methodology has been developedfor an LED street lamp system powered by a weakly regulated renewable small power grid. It has been successfully incorporated in the proposed passive LED ballast, such that the LED system can provide the least output luminous fluctuation against line voltage variation. It is envisaged that, with the proposed design methodology, such lighting system will not only provide high reliability, with potential lifetime exceeding 10 years, but with a proven feature of reduced light fluctuation, furthermore, it is found that the passive LED system can act as a smart load and has the potential of reducing the energy storage requirement for smart grids. These merits are attractive to public lighting systems powered by future renewable power grids.published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy
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De, Simoni Giorgio. "From anti-bunching to lasing: planar junctions in semiconductor heterostructures." Doctoral thesis, Scuola Normale Superiore, 2013. http://hdl.handle.net/11384/85866.
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Solomon, Ramzi, P. Pillay, and A. B. Sebitosi. "An automotive interior lighting application using white light-emitting diodes." Thesis, Cape Town : Cape Town University, 2008. http://hdl.handle.net/10019.1/357.
Full textAbstract:
Thesis (MScEng (Department of Electrical Engineering))--University of Cape Town, 2008.Energy drives technological societies. Developing countries such as South Africa are caught between the desperate need for economic growth and the emerging obligations to the environment. Efficient technologies can be used to mitigate the impact of these seemingly conflicting requirements in urban and rural environments. In this thesis the commercially available white light-emitting diode (LED) with its inherent efficiency, longevity and mechanical strength, is used to show, that success in energy efficiency can be obtained. Two cases are used to illustrate the need for efficient demand-side technology: the electricity shortages of the Western Cape Province in South Africa and a white LED pilot project in Namulonge, Uganda. The Namulonge Solar-Home System (SHS) is analyzed with the intention of creating a more acceptable general lighting solution. The concept of appropriateness through self-determination is discussed within the context of location-specific information integrated into a design procedure. The major thrust and contribution of this thesis, however, is the design of an interior luminaire for Golden Arrow Bus Services (GABS). This is in part based on the hypothesis that application-specific information will lead to implementation and human-needs success, and is researched, designed, fabricated and then laboratory tested. The biggest challenge to be overcome was the spatial light distribution of the LED array. Thus non-imaging optical lens design became the main focus of this project as it held the key to utilizing available light while conserving the light-systems energy. Circular Fresnel and Linear Fresnel (an adaptation of the concentric design) lenses were designed. Electrical, mechanical and thermal aspects of design are also detailed. Far-field, horizontal plane detection over the specified area is used to best gain the uniformity of distribution. The four criteria namely luminance, illuminance, intensity and étendue (collection efficiency), against which each design and focal length iv configuration is compared to, are extensively explored and eventually lead to a final design. In the first designs, the area of the spatial distribution between 50% and 80% of its relative intensity is collimated. The Hybrid Circular Fresnel and Hybrid Linear Fresnel lenses now redirects the relative intensity in two areas, from 50% to 70% (creating parallel rays) and then from 70% to 100% (away from the central axis), renders a distinct difference is spatial uniformity and a reduction in the peak and offaxis located intensity. All four criteria are met, with a minor adjustment of configuration within the bus internal luminaire spacing, with the hybrid designs. It is proposed that GABS employ polished designs of the Hybrid Circular Fresnel, in any of the configurations, which have collection efficiencies ranging between 64.8% and 78.3%.
Sponsored by the Centre for Renewable and Sustainable Energy Studies, Stellenbosch University
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Allen, Steven C. "Illumination for the 21st Century: High Efficiency Phosphor-Converted Light-Emitting Diodes for Solid-State Lighting." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1186160915.
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BICUDO, LETICIA L. "Utilizacao de LEDS na prevencao de mucosite oral em paciente com linfoma de Hodgkin classico - estudo de caso." reponame:Repositório Institucional do IPEN, 2004. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11199.
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Made available in DSpace on 2014-10-09T12:49:27Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:02:29Z (GMT). No. of bitstreams: 1 10198.pdf: 2777156 bytes, checksum: 6e1e2c70e93aaa5f027c563bbe4dd7ce (MD5)
Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Instituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo
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Feng, Jian. "Power improvement of the InGaN/GaN LED /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202005%20FENG.
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Chan, Ho-kan, and 陳可芹. "Life cycle assessment of LED road lighting." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B48542611.
Full textAbstract:
It is observed that the power consumption of road lighting is increased with the length of trafficable road in Hong Kong. The energy used in road lighting is increasing, which means that the greenhouse gases (GHGs) emitted from power plant for generating electricity for road lighting is at the same time increasing.
To compare the performance of light emitted diode (LED) road lighting with road lighting of other lamp sources, literature review, life cycle assessment (LCA) and technical assessment are adopted to give an overall comparison. This research focuses more on the environmental impacts of road lighting. LCA is adopted in order to give a comprehensive view on the environmental impact of road lighting. A total of 3 different lamp sources are compared: high pressure sodium (HPS) lamp, induction lamp and light emitted diode (LED) lamp.
From the model result, it is found that due to the low power consumption and long life time, LED and induction lamp road lighting gives generally less environmental impact than HPS road lighting. As induction lamp has a longer life span than LED, the environmental impact of induction lamp road lighting is found slightly less than that of LED road lighting. Taking account the future development in LED technology, leading to longer life time, higher efficacy and lower production cost, LED road lighting is expected to be a replacement for road lighting in Hong Kong for the future.published_or_final_version
Environmental Management
Master
Master of Science in Environmental Management
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Kim, Jeomoh. "Growth and characterization of III-nitride semiconductors for high-efficient light-emitting diodes by metalorganic chemical vapor deposition." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52206.
Full textAbstract:
The engineering of carrier dynamics in the MQW active region by modifying the p-type layers in the III-nitride based visible LEDs is described in this dissertation. It was found that the holes are preferentially injected into the QW adjacent to the p-InxGa1-xN layer with lower Indium mole fraction. Enhanced hole transport with increasing Indium mole fraction in the p-InxGa1-xN:Mg layer has been shown by analyzing the EL spectra. The improved hole transport and corresponding uniform distribution was achieved presumably by the potential barrier near the p-type layer and the MQW active region resulting in a modified kinetic energy of holes which creates a hole-transport-favorable environment in the MQW active region. At the same time, the limited hole injection due to the potential barrier for holes can be overcome under high injection conditions.
The InAlN layers are widely used as an alternative high quality electron blocking layer in InGaN/GaN based visible LED structures. However, the Ga auto-incorporation of the InAlN layers has been recently reported during the growth of epitaxial layers by both MOCVD and MBE. The possible origins and a mechanism of Ga auto-incorporation of InAlN epitaxial layers were systematically investigated in this dissertation. It was found that the Ga-containing deposition on a wafer susceptor/carrier is the most dominant precursor for Ga auto-incorporation and the deposition on surrounding surfaces of quartz parts in a growth chamber is the other dominant source, while the effect of stainless-steel parts and interdiffusion of Ga atom from GaN underlayer are not critical. In addition, Mg or Cp2Mg in the growth chamber during InAl(Ga)N layer growth facilitates the auto-incorporation of Ga by modifying deposition conditions of GaN on the surrounding surfaces and the wafer susceptor/carrier. Based on experimental data of various cases, the Ga-containing deposition on any hot surfaces, which are also exposed to Indium precursor to form a liquid phase, is believed to be major origins of Ga auto-incorporation.
In an effort to enhance the light extraction efficiency (LEE) in the LEDs, the direct patterning on the top surface of a LED structure, using laser interference ablation technique, has been studied in this dissertation. The 2-dimensional hexagonal lattice array of surface patterns was generated by direct irradiation of the laser source which is the interference of three laser beams onto the top p-GaN surface, without deterioration of electrical property of p-type layer and optical properties of MQW active region. The experimental results showed approximately 20 % improved LEE of the laser-patterned LED structure compared to the conventional LED structure without surface textures. Furthermore, the theoretical calculation using Monte-Carlo ray-tracing simulation confirmed the enhancement of LEE of the laser-patterned LED structure.
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Zhang, Rong. "Wafer level LED packaging with integrated DRIE trenches for encapsulation /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?MECH%202008%20ZHANGR.
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Zhang, Fan. "QUANTUM EFFICIENCY ENHANCEMENT FOR GAN BASED LIGHT-EMITTING DIODES AND VERTICAL CAVITY SURFACE-EMITTING LASERS." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3655.
Full textAbstract:
This thesis explores the improvement of quantum efficiencies for InGaN/GaN heterostructures and their applications in light-emitting diodes (LEDs) and vertical cavity surface-emitting lasers (VCSELs). Different growth approaches and structural designs were investigated to identify and address the major factors limiting the efficiency. (1) Hot electron overflow and asymmetrical electron/hole injection were found to be the dominant reasons for efficiency degradation in nitride LEDs at high injection; (2) delta p-doped InGaN quantum barriers were employed to improve hole concentration inside the active region and therefore improve hole injection without sacrificing the layer quality; (3) InGaN active regions based on InGaN multiple double-heterostructures (DHs) were developed to understand the electron and hole recombination mechanisms and achieve high quantum efficiency and minimal efficiency droop at high injection; (4) the effect of stair-case electron injectors (SEIs) has been investigated with different active region designs and SEIs with optimized thickness greatly mitigated electron overflow without sacrificing material quality of the active regions. The active regions showing promising performance in LEDs were incorporated into VCSEL designs. Hybrid VCSEL structures with bottom semiconductor AlN/GaN and a top dielectric SiO2/SiNx DBRs have been investigated, and quality factors as high as 1300 have been demonstrated. Finally, VCSEL structures with all dielectric DBRs have been realized by employing a novel ELO-GaN growth method that allowed integration of a high quality InGaN cavity active region with a dielectric bottom DBR without removal of the substrate while forming a current aperture through the ideally dislocation-free region. The full-cavity structures formed as such exhibited quality factors 500 across the wafer.
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Fonseca, Zito Palhano da. "Sistemas eletrônicos com elevado fator de potência de estágio único e sem capacitores eletrolíticos para acionar LEDs de potência." Universidade Tecnológica Federal do Paraná, 2014. http://repositorio.utfpr.edu.br/jspui/handle/1/1575.
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Este trabalho propõe a utilização de dois conversores de estágio único e elevado fator de potência para acionar LEDs de potência sem a utilização de capacitores eletrolíticos no barramento CC. Ambas as topologias podem operar com entrada universal, dimerização da corrente de saída e comando auto-oscilante. No entanto o número de dispositivos semicondutores é maior em relação aos conversores estáticos de energia convencionais. A correção do fator de potência do primeiro conversor proposto é obtida através de uma conexão direta realizada por um indutor inserido entre o estágio inversor de saída e dois capacitores conectados antes do estágio retificador de entrada criando um caminho alternativo para a corrente fornecida pela fonte de alimentação CA entre estes estágios. O segundo conversor realiza a correção do fator de potência através de dois indutores acoplados magneticamente conectados na entrada da ponte retificadora. Estes indutores também operam em conjunto com os dois capacitores de entrada e, por possuírem acoplamento subtrativo, processam energia de forma complementar propiciando um volume de núcleo reduzido em relação ao indutor da primeira topologia proposta. Em ambas as topologias apresentadas, a corrente da fonte de alimentação CA fornece energia instantânea com o dobro da frequência de comutação aplicada ao estágio inversor, permitindo a redução do filtro LC necessário na entrada do sistema. As correntes contínuas aplicadas aos LEDs das duas topologias são obtidas através de pontes retificadoras com filtros capacitivos conectados entre os estágios inversores e os pontos centrais de dois capacitores dos barramentos CC. Resultados de simulação e experimentais utilizando 12 LEDs conectados em série com potência total de 45 W, alimentados em 127 V e 220 V são apresentados para validarem as metodologias de projetos propostas.Two single-stages high-power-factors converters without DC bus electrolytic capacitors for power LEDs applications are proposed in this work. The power factor correction of the first proposed topology is obtained through direct link of one boost inductor connected between the output inverter stage and two capacitors placed before of input bridge rectifier. In the second proposed lighting system, the power factor correction is performed by two magnetically coupled inductors placed at input bridge rectifier that also operate with the two input capacitors and the output inverter stage. In this case, the coupled inductors magnetic fluxes are complementary and their core is reduced when compared with the inductor of the first proposal. In both converters the input voltage provides instantaneous ripple current with twice switching frequency of the output inverter and the input filter inductor is reduced. To obtain continuous current on the LEDs, one output rectifier placed between output inverter stage and a neutron point (NP) of the two DC bus capacitors is used. The LEDS current is limited by a serie inductor. Through steady-state operation the main theorical waveforms as well as the converters design methodologies are presented. To verify the theoretical analysis carried out, simulation and experimental results are also presented. To verify the theoretical analysis, also simulation and experimental results using 12 LEDs connected in series with a power of 45 W, suplied at 127 V and 220 V are presented to validate the methodology proposed projects.
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Remella, Siva Rama Karthik. "Operation and Heuristic Design of Closed Loop Two-Phase Wicked Thermosyphons (CLTPWT) for Cooling Light Emitting Diodes (LEDs)." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522314073895889.
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Monavarian, Morteza. "Beyond conventional c-plane GaN-based light emitting diodes: A systematic exploration of LEDs on semi-polar orientations." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4198.
Full textAbstract:
Despite enormous efforts and investments, the efficiency of InGaN-based green and yellow-green light emitters remains relatively low, and that limits progress in developing full color display, laser diodes, and bright light sources for general lighting. The low efficiency of light emitting devices in the green-to-yellow spectral range, also known as the “Green Gap”, is considered a global concern in the LED industry. The polar c-plane orientation of GaN, which is the mainstay in the LED industry, suffers from polarization-induced separation of electrons and hole wavefunctions (also known as the “quantum confined Stark effect”) and low indium incorporation efficiency that are the two main factors that contribute to the Green Gap phenomenon. One possible approach that holds promise for a new generation of green and yellow light emitting devices with higher efficiency is the deployment of nonpolar and semi-polar crystallographic orientations of GaN to eliminate or mitigate polarization fields. In theory, the use of other GaN planes for light emitters could also enhance the efficiency of indium incorporation compared to c-plane.
In this thesis, I present a systematic exploration of the suitable GaN orientation for future lighting technologies. First, in order to lay the groundwork for further studies, it is important to discuss the analysis of processes limiting LED efficiency and some novel designs of active regions to overcome these limitations. Afterwards, the choice of nonpolar orientations as an alternative is discussed. For nonpolar orientation, the (1-100)-oriented (m-plane) structures on patterned Si (112) and freestanding m-GaN are studied. The semi-polar orientations having substantially reduced polarization field are found to be more promising for light-emitting diodes (LEDs) owing to high indium incorporation efficiency predicted by theoretical studies. Thus, the semi-polar orientations are given close attention as alternatives for future LED technology.
One of the obstacles impeding the development of this technology is the lack of suitable substrates for high quality materials having semi-polar and nonpolar orientations. Even though the growth of free-standing GaN substrates (homoepitaxy) could produce material of reasonable quality, the native nonpolar and semi-polar substrates are very expensive and small in size. On the other hand, GaN growth of semi-polar and nonpolar orientations on inexpensive, large-size foreign substrates (heteroepitaxy), including silicon (Si) and sapphire (Al2O3), usually leads to high density of extended defects (dislocations and stacking faults). Therefore, it is imperative to explore approaches that allow the reduction of defect density in the semi-polar GaN layers grown on foreign substrates.
In the presented work, I develop a cost-effective preparation technique of high performance light emitting structures (GaN-on-Si, and GaN-on-Sapphire technologies). Based on theoretical calculations predicting the maximum indium incorporation efficiency at θ ~ 62º (θ being the tilt angle of the orientation with respect to c-plane), I investigate (11-22) and (1-101) semi-polar orientations featured by θ = 58º and θ = 62º, respectively, as promising candidates for green emitters. The (11-22)-oriented GaN layers are grown on planar m-plane sapphire, while the semi-polar (1-101) GaN are grown on patterned Si (001).
The in-situ epitaxial lateral overgrowth techniques using SiNx nanoporous interlayers are utilized to improve the crystal quality of the layers. The data indicates the improvement of photoluminescence intensity by a factor of 5, as well as the improvement carrier lifetime by up to 85% by employing the in-situ ELO technique. The electronic and optoelectronic properties of these nonpolar and semi-polar planes include excitonic recombination dynamics, optical anisotropy, exciton localization, indium incorporation efficiency, defect-related optical activities, and some challenges associated with these new technologies are discussed. A polarized emission from GaN quantum wells (with a degree of polarization close to 58%) with low non-radiative components is demonstrated for semi-polar (1-101) structure grown on patterned Si (001). We also demonstrated that indium incorporation efficiency is around 20% higher for the semi-polar (11-22) InGaN quantum wells compared to its c-plane counterpart. The spatially resolved cathodoluminescence spectroscopy demonstrates the uniform distribution of indium in the growth plane. The uniformity of indium is also supported by the relatively low exciton localization energy of Eloc = 7meV at 15 K for these semi-polar (11-22) InGaN quantum wells compared to several other literature reports on c-plane. The excitons are observed to undergo radiative recombination in the quantum wells in basal-plane stacking faults at room temperature. The wurtzite/zincblende electronic band-alignment of BSFs is proven to be of type II using the time-resolved differential transmission (TRDT) method. The knowledge of band alignment and degree of carrier localization in BSFs are extremely important for evaluating their effects on device properties. Future research for better understanding and potential developments of the semi-polar LEDs is pointed out at the end.
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Varnava, Christiana. "Quantum dot-based Entangled-Light Emitting Diodes (E-LED) for quantum relays." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/271783.
Full textAbstract:
Sources of entangled pairs of photons can be used for encoding signals in quantum-encrypted communications, allowing a sender, Alice, and a receiver, Bob, to exchange keys without the possibility of eavesdropping. In fact, any quantum information system would require single and entangled photons to serve as qubits. For this purpose, semiconductor quantum dots (QD) have been extensively studied for their ability to produce entangled light and function as single photon sources. The quality of such sources is evaluated based on three criteria: high efficiency, small multi-photon probability, and quantum indistinguishability. In this work, a simple quantum dot-based LED (E-LED) was used as a quantum light source for on-demand emission, indicating the potential for use as quantum information devices. Limitations of the device include the fine-structure splitting of the quantum dot excitons, their coherence lengths and charge carrier interactions in the structure. The quantum dot-based light emitting diode was initially shown to operate in pulsed mode under AC bias frequencies of up to several hundreds of MHz, without compromising the quality of emission. In a Hong-ou-Mandel interference type experiment, the quantum dot photons were shown to interfere with dissimilar photons from a laser, achieving high two-photon interference (TPI) visibilities. Quantum entanglement from a QD photon pair was also measured in pulsed mode, where the QD-based entangled-LED (E-LED) was electrically injected at a frequency of 203 MHz. After verifying indistinguishability and good entanglement properties from the QD photons under the above conditions, a quantum relay over 1km of fibre was demonstrated, using input qubits from a laser source. The average relay fidelity was high enough to allow for error correction for this BB84-type scheme. To improve the properties of the QD emission, an E-LED was developed based on droplet epitaxy (D-E) QDs, using a different QD growth technique. The relevant chapter outlines the process of QD growth and finally demonstration of quantum entanglement from an electrically injected diode, yielding improvements compared to previous E-LED devices. For the same reason, an alternative method of E-LED operation based on resonant two-photon excitation of the QD was explored. Analysis of Rabi oscillations in a quantum dot with a bound exciton state demonstrated coupling of the ground state and the biexciton state by the external oscillating field of a laser, therefore allowing the transition between the two states. The results include a considerable improvement in the coherence length of the QD emission, which is crucial for future quantum network applications. We believe that extending this research can find application in quantum cryptography and in realising the interface of a quantum network, based on semiconductor nanotechnology.
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Phillipps, Nathan. "Design and Construction of a Tunable Light Source with Light Emitting Diodes for Photosynthetic Organisms." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1399.
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This thesis describes and documents the design and construction of a light source which is tunable and has the ability to mimic the spectral output of the sun in the photosynthetic active radiation range (400 - 700 nm). To adjust the spectral output at different wavelengths different types of LEDs were chosen and combined. This thesis describes the design, construction, testing, and suggestions for further improvements to this light source. The light source is comprised of 900 LEDs with 26 different peak wavelengths within the photosynthetically active radiation range. The light source is made tunable through the use of a control system utilizing pulse width modulation. This unique light source will allow studies to be performed to understand spectral influences on microalgae and lipid production as well as other photosynthetic organisms.
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LI, WEIXIN. "A HYBRID DEVICE APPROACH TO HIGH PERFORMANCE IN ORGANIC LIGHT-EMITTING DIODES." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1148051195.
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Hudson, Andrew Ian. "Output limitations to single stage and cascaded 2-2.5μm light emitting diodes." Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/1468.
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Since the advent of precise semiconductor engineering techniques in the 1960s, considerable effort has been devoted both in academia and private industry to the fabrication and testing of complex structures. In addition to other techniques, molecular beam epitaxy (MBE) has made it possible to create devices with single mono-layer accuracy. This facilitates the design of precise band structures and the selection of specific spectroscopic properties for light source materials.
The applications of such engineered structures have made solid state devices common commercial quantities. These applications include solid state lasers, light emitting diodes and light sensors. Band gap engineering has been used to design emitters for many wavelength bands, including the short wavelength (SWIR) infrared region which ranges from 1.5 to 2.5 μm [1]. Practical devices include sensors operating in the 2-2.5 μm range. When designing such a device, necessary concerns include the required bias voltage, operating current, input impedance and especially for emitters, the wall-plug efficiency. Three types of engineered structures are considered in this thesis. These include GaInAsSb quaternary alloy bulk active regions, GaInAsSb multiple quantum well devices (MQW) and GaInAsSb cascaded light emitting diodes.
The three structures are evaluated according to specific standards applied to emitters of infrared light. The spectral profiles are obtained with photo or electro-luminescence, for the purpose of locating the peak emission wavelength. The peak wavelength for these specimens is in the 2.2-2.5μm window. The emission efficiency is determined by employing three empirical techniques: current/voltage (IV), radiance/current (LI), and carrier lifetime measurements. The first verifies that the structure has the correct electrical properties, by measuring among other parameters the activation voltage. The second is used to determine the energy efficiency of the device, including the wall-plug and quantum efficiencies. The last provides estimates of the relative magnitude of the Shockley Read Hall, radiative and Auger coefficients. These constants illustrate the overall radiative efficiency of the material, by noting comparisons between radiative and non-radiative recombination rates.
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Abdulahi, Mohamed Abdirahman, and Wännström Aksel. "Quality Control of Light Emitting Diodes : Using power factor, harmonic distortion and light to power ratios." Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-301196.
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This study addresses quality control for Light Emitting Diodes (LED) according to fouraspects, the power factor of LED lamps, their harmonics and total harmonic distortion (THD), the luminosity for total power to radiated power ratio. It focuses on four brands and six different LED lamps, and concludes that IKEA's LED lamps pertain as the quality lamp, with a power factor over 0.9, THD less than 4% and a power to radiated light of over 4%.
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Massabuau, Fabien Charles-Paul. "The impact of the nanostructure of InGaN/GaN quantum wells on LED efficiency." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708520.
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Tran, Thu, and thutran55@yahoo com au. "New Radiochromic Film Densitometry System Using Commercially Available Digital Camera and LEDs." RMIT University. Applied Sciences, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080528.112722.
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This project involved designing and building a radiochromic film (RCF) densitometer using a still digital camera as the light detector and light emitting diode, LED, as the light source. The behaviour of the LED and charged coupled device (CCD) in the still digital camera, under different light exposure settings (by changing LED current and camera shutter speed) were measured and an optimal setting was determined. Additionally, methods were devised and tests were carried out in order to spread the illumination area of the single light source. Uniform spreading of the LED illumination area was possible by the use of two diffusers placed at an optimum separation distance that was determined in this work. The usefulness of this custom-made RCF densitometer was demonstrated by using this device to image exposed RCF and using the film analysis software, Image J, to determine the film absorbed dose. Two clinical situations were examined: open and virtual wedge radiation beams. It was concluded that still digital cameras can be used in RCF densitometers provided they can capture and store raw images, a single diffused LED can illumination an area large enough for RCF densitometry and appropriate film analysis software is needed to extract and handle the large volume of greyscale data from the RCF.
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Ha, Min Seok. "Thermal analysis of high power led arrays." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31803.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Samuel Graham; Committee Member: J. Rhett Mayor; Committee Member: Yogendra Joshi. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Freymiller, Aaron Troy. "LED shipboard lighting a comparative analysis." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FFreymiller.pdf.
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Thesis (Master of Business Administration)--Naval Postgraduate School, December 2009.Thesis Advisor(s): Dew, Nicholas. Second Reader: Hudgens, Bryan. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: Lighting, LEDs, shipboard lighting. Includes bibliographical references (p. 31-32). Also available in print.
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Leng, Sovannarith. "Identifying and evaluating aging signatures in light emitting diode lighting systems." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30035/document.
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Dans ce travail, les dégradations des diodes électroluminescentes (DEL) ont été étudiées en identifiant et en évaluant leurs signatures électriques et photométriques en vieillissement accéléré sous stress thermique et électrique. Un prototype de banc de test expérimental a été développé et construit spécifiquement pour cette étude ce qui nous a permis de tester 128 échantillons en appliquant différentes conditions de stress thermiques et électriques. Quatre types différents de DEL ont été étudié avec des caractéristiques techniques similaires (température de couleur, courant nominal, mono-puce,...) mais avec des technologies différentes couvrant les principaux acteurs du marché (Cree, Osram, Philips et Seoul Semiconductor). Les échantillons ont d'abord été caractérisés à leur état initial, puis soumis à des conditions de stress électrique (à 350mA ou 1050mA) et thermique (fixé à 50°C). Les mécanismes de défaillance ont été analysés en étudiant l'évolution des signatures électriques et photométriques. Ces caractérisations ont permis d'évaluer et de déterminer l'origine des dégradations à différents niveaux : puce semi-conductrice, interconnexions, phosphore ou encapsulation du dispositif. Les caractérisations électriques nous ont permis d'identifier les mécanismes de dégradation de la puce semi-conductrice et de déterminer la nature des dégradations au niveau du contact ohmique du dispositif (sous fort courant injecté). Les caractérisations photométriques complètent cette étude en évaluant les dégradations associées à l'optique (encapsulation et packaging)In this work, the degradation of light emitting diodes (LEDs) is studied by identifying and evaluating their aging signature during the stress time. The custom-made experimental test bench is built for realization of the test measurement. Through this experimental test bench, it allows to test a large amount of LED samples and enable to select different temperature condition and different current stress level. There are four different types of LED with similar characteristic in term of their color temperature, IF, VF, power (1W) and as monochip, but different technology coming from Cree, Osram, Philips and Seoul Semiconductor. The devices are firstly characterized their electrical and photometrical characteristic at their initial state, then they are submitted to different current stress condition at low current stress (350mA) and high current stress (1000mA) while the thermal stress is fixed at one temperature (50°C). The study of these devices failure mechanism is archived by using the primary method based on the electrical and photometrical characterization of the devices that allows to evaluate their degradation at different locations of the device components such as semiconductor chip, interconnection and device's package. The electrical characteristic of the device's I-V curve: at low injected current level and reverse bias allow us to identify the degradation characteristic of device's semiconductor chip, at high injected current level allows us to determine the degradation of device's ohmic contact and photometric characteristic allows us to evaluate the degradation of device's package system
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Cizek, Christopher J. "Shipboard LED lighting a business case analysis." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FCizek.pdf.
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Thesis (Master of Business Administration)--Naval Postgraduate School, December 2009.Thesis Advisors: Dew, Nicholas ; Mutty, John. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: LED lighting, solid state lighting, business case analysis. Includes bibliographical references (p. 81-83). Also available in print.
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Sebkhi, Nordine. "A study of efficiency droop of green light emitting diodes grown by metalorganic chemical vapor deposition." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42856.
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The objective of this thesis is to discuss the solutions investigated by AMDG (Advanced Materials and Devices Group) to reduce the "efficiency droop" effect that occurs in III-Nitrides Light Emitting Diodes (LEDs) when driven at high injection current densities. The efficiency droop refers to a decrease of the LED light emission efficiency when increases the current density from low values ~10 A/cm2 to higher values >100A/cm2. Many scientific papers have been written about the possible reasons for this phenomenon. Therefore, this thesis will discuss the different effects suspected to contribute to the droop, and discuss LED structure modifications studied by Dr. Dupuis' research group to reduce their impact. In addition to a description of a conventional LED structure, a discussion of the device fabrication process will be provided including the solutions investigated in our group to improve LED performance.
Because measurement is critical to our studies, a description of the equipment used by the AMDG will be provided, e.g., the Electroluminescence (EL) and Photoluminescence (PL) test stations, Atomic Force Microscopy (AFM) for surface topology, TLM for metallic contact resistivity, X-Ray diffraction for crystal quality and epitaxial layer structure, and Hall-Effect measurement for doping concentration characterization and material resistivity.
Because the IQE gives us a direct assessment of the active region's crystal quality, the setup and operation of a new Temperature-Dependent PL (TD-PL) system to measure the Internal Quantum Efficiency (IQE) was the main focus of this research. The External Quantum Efficiency (EQE) is measured using electroluminescence measurements. The EL measurements involve the acquisition of the emitted light spectrum along with different processed data such as the Full-Width at Half Maximum (FWHM) of the spectral intensity, the peak wavelength, output power, etc., which allows a comparison of the different LED structure performances.
Within this work, a new LabVIEW© program (called QuickTest 2.0) has been developed in order to automate the instrumentation setup and improve both the speed and accuracy of EL acquisition.
A brief description of the G language used by the LabVIEW© software will be provided along with the objective and motivation for upgrading the program, the general features of the program, and a comparison of spectrum acquisition and processed data results. The benefit for the research in the AMDG was to reduce measurement time, improve efficiency, supply a more user-friendly front-panel, and to enable transfer to other computers.
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Li, Shuo. "Multiple-LED color-sequential liquid crystal on silicon projector /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?ECED%202008%20LIS.
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Allanche, Timothé. "Effect of high radiation doses (MGy) on light Emitting Diodes and optical glasses." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSES039.
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Le projet CAMRAD répond à un appel à projets PIA de l’Agence Nationale pour la gestion des Déchets RAdioactifs (ANDRA) en vue de faciliter la gestion des déchets nucléaires, dont le volume va considérablement augmenter avec le démantèlement du parc nucléaire français. Celui-ci prévoit la conception d’une caméra à Haute Définition durcie aux radiations à des doses au moins dix fois supérieures aux caméras actuellement disponibles. Cette thèse porte sur les effets des rayonnements (jusqu’au MGy) sur les LEDs rendant la caméra autonome en termes de lumière et les verres optiques nécessaires à la réalisation de son système optique. Après une description du projet, les besoins en termes d’éclairage sont détaillés. Les principales innovations de ce travail sont la qualification au MGy de nombreuses LEDs commerciales, des mesures post-irradiation de leurs angles d’émission et des mesures en ligne sous rayon-X. La troisième partie concerne les verres optiques sous radiation. Après avoir détaillé comment le dopage au cérium des verres dits « durci » les protège contre le noircissement causé par les radiations, nous montrons qu’il existe un manque dans la littérature sur les effets des fortes doses. Pour le combler et améliorer les mesures d’atténuation induites, nous avons développé un montage optique permettant de mesurer le noircissement des verres pendant l’irradiation plutôt qu’a posteriori. Il nous a permis de réaliser des mesures systématiques sur des verres durcis et standards en fonction du débit de dose et de la température. Ainsi nous avons montré que certains verres standards présentent un fort potentiel pour une utilisation à des doses de radiations de l’ordre du MGy. L’approche suivie a mené au dépôt d’un brevetThe CAMRAD project responds to the PIA call for proposals from the French National Agency for Radioactive Waste Management with the aim of finding new solutions for radioactive waste management in prevision of its strong increase due to the dismantling of the current French nuclear facilities. The project aims to design a high-definition, radiation-hardened, camera capable to withstand radiation dose levels at least ten times higher than the currently available cameras. This PhD thesis deals with the effects of radiation (up to the MGy) on LEDs allowing the camera to be autonomous in terms of lightning and the optical glasses to be used for the realization of optical system. After a description of CAMRAD, the requirement in terms of lighting are detailed. The main innovations of this work are the qualification at the MGy level of numerous commercial LEDs, post-irradiation measurements of their emission angles and online X-ray measurements. The third part concerns radiation effect on optical glasses. After detailing how Cerium doping of so-called "hardened" glasses protects them from darkening under radiation, we show that there is a lack of literature on the effects of high doses. In order to fill it and to improve the radiation induced attenuation measurements, we have developed an optical set-up allowing to measure the darkening of glasses during irradiation rather than post mortem. We carried systematic measurements on hardened and standard glasses as a function of dose rate and temperature. We have shown that certain standard optical glasses are highly promising for use at MGy dose levels, the followed approach has led to the filing of a patent
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Barroso, Angel. "Optimisation des systèmes d'éclairage des bâtiments de l'Université Paul Sabatier basé sur un réseau novateur de type bus continu/basse tension." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30345/document.
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Les diodes électroluminescentes (LEDs) constituent de nouvelles solutions pour créer des luminaires plus robustes, ayant un meilleur rendement de conversion et plus respectueuses de l'environnement. Malgré les avantages indiscutables déjà obtenus aujourd'hui, ce type de luminaire présente encore quelques optimisations possibles et offre des possibilités de fonctionnalités multiples. A travers plusieurs campagnes de tests, l'auteur montre sur des LEDs du commerce, que les points d'optimisation non encore exploités dans les luminaires commerciaux. Ces LEDs ont ainsi été testés sur de larges plages de fonctionnement du point de vue photométrique, électrique mais aussi thermique pour connaitre la reproductibilité des résultats obtenus. Ainsi les influences des conditions d'utilisation notamment en température de fonctionnement et niveaux de courant d'alimentation ont été étudiées. Pour dimensionner au mieux une alimentation électrique spécifique, une recherche de modèles de LED élémentaires a été effectuée. L'objectif est que les modèles tiennent compte des principaux paramètres mais soit suffisamment simple pour être inséré dans un environnement système afin de simuler le luminaire dans son environnement complet. Ainsi, l'étude comparative de plusieurs associations de LEDs a été effectuée permettant d'en déduire des compromis pour proposer de nouvelles solutions faibles consommatrices d'énergie à coût réduit incluant de nouveaux types d'alimentationLight emitting diodes (LEDs) bring new possibilities to get luminaires more robust with an improved efficiency and more environmentally respectfull. Despite the benefits already achieved today, this type of luminaire still presents some possible optimizations and provides opportunities for multiple features. Through several tests, the author shows on LEDs in market that optimization points are not operated in commercial luminaires. These LEDs have been tested over a wide range of operation in photometric, electrical but also thermal to know the reproducibility of the results. Thus the influences of operating conditions including operating temperature and supply current levels were studied. To design a specific power supply for each LED type, a search of elementary LED models was performed. The objective is to take into account the main parameters of the models but also to be enough simple to be inserted into a system environment to simulate the luminaire in whole environment. Thus, the comparative study of several associations of LEDs was conducted to deduce the best compromise and propose new solutions to reduce energy consumptions and production costs, including new types of power supply
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Zhang, Kai. "Carbon nanotube thermal interface material and its application in high brightness LED packages /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?MECH%202008%20ZHANG.
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