Dissertations / Theses on the topic 'InGaN'
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Li, Shunfeng. "Growth and characterization of cubic InGaN and InGaN/GaN quantum wells." kostenfrei, 2005. http://ubdata.uni-paderborn.de/ediss/06/2005/li/.
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Brown, James. "Carrier Dynamics in InGaN." Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486547.
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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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Van, der Laak Nicole Kathleen. "Nano-modified InGaN quantum wells." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612841.
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Niu, Nan. "GaN/InGaN Microcavities and Applications." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17467361.
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Semiconductor micro- and nano-cavities are excellent platforms for experimental studies of optical cavities, lasing dynamics, and cavity Quantum Electrodynamics (QED). Common materials for such experiments are narrow bandgap semiconductor materials with well-developed epitaxial growth technologies, such as GaAs and InP, among others. Gallium nitride (GaN) and its alloys are industrially viable materials with wide direct bandgaps, low surface re-combination velocities, and large exciton binding energies, offering the possibility of room temperature realization of light-matter interaction. Controlling light-matter interaction is at the heart of nanophotonic research which leads to ultra-low threshold lasing, photonic qubits, and optical strong coupling. Technologically, due to its blue emission, GaN photonic cavities with indium gallium nitride (InGaN) active mediums serve as efficient light sources for the fast growing photonic industry, optical computing and communication networks, display technology, as well as quantum information processing.
The main challenges in fabricating high quality GaN cavity are due to its chemical inertness and low material quality as a result of strain-induced defects and threading dislocations. In this dissertation, I examine the designs, novel fabrication processes, and characterizations of high quality factor GaN microdisk and photonic crystal nanobeam cavities with different classes of InGaN active medium, namely quantum dots (QDs), quantum wells (QWs), and fragmented quantum wells (fQWs), for investigating light-matter interaction between cavity and these active media.
This dissertation is carefully organized into four chapters. Chapter 1 outlines the background of the research, the materials and growth, and the necessary technique Photoelectrochemical (PEC) etching which is uniquely used to undercut and suspend GaN cavities.
Chapter 2 outlines the fabrications, optical experiments, and tuning technique developed for GaN/InGaN microdisks. Microdisks are circular resonant cavities that support whispering gallery modes. Through the use of optimized dry etching and PEC, high quality factor microdisks with relatively small modal volume are fabricated with immediate demonstration of low threshold lasing. On the path to achieving light and matter interactions, irreversible tuning of the cavity mode of p-i-n doped GaN/InGaN microdisks is achieved through photo-excitation in a water environment. Such a technique paves the way for deterministically and spectrally matching the cavity mode to the emitter’s principle emission.
Chapter 3 outlines the work done on the high quality GaN photonic crystal nanobeams with InGaN QDs and fQWs. The fragmented nature of the fQW layer has a surprisingly dramatic influence on the lasing threshold. A record low threshold is demonstrated that is an order of magnitude lower in threshold than identical nanobeams with homogeneous QW, and comparable to the best devices in other III-V material systems. As an active medium with greater carrier confinement than quantum wells, and higher carrier capture probability than quantum dots, the fQW active medium, in combination with the nanobeam cavity with ultra-small modal volume and high quality factor, provides an ideal means of probing the limits of light and matter interactions in the nanoscale. Moreover, GaN/InGaN nanopillars are fabricated to isolate a single InGaN QD for understanding its emission properties. Antibunching is observed, demonstrating the quantum nature of the QD emission. Gas tuning is attempted on GaN nanobeams with InGaN QDs to achieve QD-cavity mode coupling and to demonstrate cavity enhanced single photon emission. Last but not least, Chapter 4 concludes the dissertation with summary and future directions.Engineering and Applied Sciences - Applied Physics
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Wallace, Michael. "Optoelectronic study of InGaN/GaN LEDs." Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27451.
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The quality of light emitting diodes (LEDs) has increased to a point where solid state lighting is becoming fairly common. Despite this, greater understanding of the effect of the device structure and the electric fields within them is helpful to continue improving device efficiency and uniformity and in reducing costs. In this thesis the optical and electronic properties of InGaN/GaN LEDs have been studied with a combination of luminescence spectroscopy, microscopy, conductivity mapping and efficiency measurements. A study was made of the effects of the various electric fields, and the interplay between them, on LED luminescence and conductivity. Cathodoluminescence (CL) mapping shows die to die variation across large wafers revealing the powerful effects of a induced electric field on spectral intensity/position/width, in uncontacted devices. Micron scale spots in the LED material, lower in luminescence intensity and which trap charge, were revealed by CL/EBIC mapping with the origin attributed to cluster point defects in the active region. Depth resolved CL and CL under bias reveal the extent of asymmetry in carrier transport in the p/n type GaN around the active region. LEDs grown with different active region temperature profiles were studied. Devices exposed to high temperature after quantum well growth (2T) were found to have a uniform spatial luminescence and a peak efficiency that is higher and occurs at a lower current density (0.1 W/A @ 1 Acm¯²). By contrast those with a low temperature cap (Q2T) exhibit dark spots in the luminescence, and a lower peak efficiency at a higher current density (0.04 W/A @ 10 Acm¯²). The effect of improvement in LED design and material quality on the device efficiency, uniformity and spectral characteristics was studied. The addition of an Al₀.₂₃Ga.₇₇N electron blocking layer (EBL) was found to reduce the size and strength of the dark spots by about a factor of 2, while an additional In₀.₀₅Ga₀.₉₅N underlayer (UL) removed the dark spots entirely and shifted the luminescence peak by around 100 meV. The effect on the electroluminescence efficiency of the reduction in template dislocation density was found to depend strongly on the drive current density, with defect non-radiative recombination more important at low currents. Overall device efficiency was shown to be improved with an EBL and UL. The most efficient devices were those with the 2T type growth but the relative improvements are larger in LEDs grown with the Q2T method. Together, the results present a number of factors limiting the performance of current LEDs and suggest potential routes for improvement and optimisation.
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Olaizola, S. M. "Ultrafast spectroscopy of InGaN quantum wells." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414678.
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Griffin, Chris. "Applications of micropixellated InGaN LED arrays." Thesis, University of Strathclyde, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425904.
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Smeeton, Timothy Michael. "The nanostructures of InGaN quantum wells." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614901.
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Li, Quantong. "Strain relaxation in InGaN/GaN herostructures." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC204/document.
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Dans ce travail, nous avons étudié la relaxation de couches d’hétérostructures InGaN/GaN obtenue par épitaxie en phase vapeur aux organométalliques (EPVOM) et épitaxie aux jets moléculaires (EJM) principalement par microscopie électronique en transmission (MET). Pour ce faire, nous avons fait varier la composition de l'indium de 4.1% au nitrure d'indium pur, ce qui correspond lors de la croissance sur GaN à un décalage paramétrique allant de 1% à 11.3%. Le travail a porté sur des couches dont l’épaisseur allait de 7 nm à 500 nm. A partir d’une composition en indium voisine de 10%, nous mettons en évidence la formation d’un réseau de dislocations vis dont la ligne se promène dans l’interface, avec de très longues sections droites le long des directions <11-20>. Ces dislocations coexistent avec un réseau de dislocations coins qui commence à se former vers 13%, il disparait complétement autour d’une composition en indium de 18%. Le réseau de dislocation vis se densifie de plus en plus au-delà. Outre ces dislocations de décalage paramétrique, d'autres mécanismes qui contribuent à la relaxation de la contrainte dans ces hétérostructures InGaN/GaN ont été mis en évidence. Ainsi, au-dessus d'une composition d'indium supérieure à 25%, de nombreux phénomènes se produisent simultanément. (1) Formation des dislocations de décalage paramétrique à l'hétérointerface; (2) une composition de la couche qui s’enrichit en indium vers la surface; (3) des fortes perturbations de la séquence hexagonale conduisant à un empilement aléatoire; (4) croissance à trois dimensions (3D) pouvant même conduire à des couches poreuses lorsque la composition en indium est comprise entre 40% et 85%. Cependant, on met en évidence qu’il est possible de faire croître de l’InN pur de bonne qualité cristalline s'améliore grâce à la formation systématique d'une couche 3DIn this work, we have investigated the strain relaxation of InGaN layers grown on GaN templates by MOVPE and PAMBE using TEM. To this end we varied the indium composition from 4.1% to pure indium nitride and the corresponding mismatch was changing from less than 1% to 11.3%, the thickness of the InGaN layers was from 7 nm to 500 nm. When the indium composition is around 10%, one would expect mostly elastically strained layers with no misfit dislocations. However, we found that screw dislocations form systematically at the InGaN/GaN interface. Moreover, below 18% indium composition, screw and edge dislocations coexist, whereas starting at 18%, only edge dislocations were observed in these interfaces. Apart from the edge dislocations (misfit dislocations), other mechanisms have been pointed out for the strain relaxation. It is found that above an indium composition beyond 25%, many phenomena take place simultaneously. (1) Formation of the misfit dislocations at the heterointerface; (2) composition pulling with the surface layer being richer in indium in comparison to the interfacial layer; (3) disruption of the growth sequence through the formation of a random stacking sequence; (4) three dimentional (3D) growth which can even lead to porous layers when the indium composition is between 40% and 85%. However, pure InN is grown, the crystalline quality improves through a systematic formation of a 3D layer
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Alam, Saiful. "Optimisation d’hétéro-structures à multipuits quantiques InGaN sur sous-couche InGaN pour diodes electroluminescentes émettant dans le domaine spectral bleu-vert." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0050/document.
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Les diodes électroluminescentes (DEL) à base de GaN ont déjà été commercialisées comme solution économique d’éclairage, étant donné que les multi-puits quantiques (MQW) basés sur InGaN/GaN peuvent être conçus pour produire de la lumière dans toute la gamme spectrale visible. Pour obtenir une émission de lumière blanche, la conversion à base de phosphore conduit à une faible efficacité due à la perte de Stokes et peut également produire un faible indice de rendu des couleurs (IRC). Par conséquent, pour une efficacité élevée et une lumière blanche avec un IRC élevé, la génération de lumière blanche par combinaison rouges-vertes-bleues (RGB) est nécessaire. La DEL bleue basée sur InGaN/GaN présente une bonne performance aujourd'hui. La DEL rouge à base de III-phosphure est également très efficace. Cependant, avec des longueurs d'onde intermédiaires pour l'émission de spectre vert, l'efficacité des dispositifs diminue avec l'augmentation de la composition d’indium (In) dans la région active à cause de l'épitaxie selon la direction de GaN communément utilisée (0001-Ga). Ce «green-gap» est le principal obstacle pour obtenir une DEL blanche sans phosphore. Les structures DEL non ou semi-polaires pourraient être une solution pour réduire ou omettre le problème de polarisation, cependant, une croissance plus facile de bonne qualité cristalline avec moins d'étapes de fabrication font que la croissance de la direction (0001-Ga) est toujours commercialement prometteuse. Par conséquent, une conception de structure optimisée pour atténuer la polarisation et augmenter l'émission optique provenant d'hétéro-structures élaborées dans cette direction de croissance est toujours demandée. Les structures de DEL classiques multi-puits quantiques (MQW) InGaN/GaN sont développées sur une template GaN et utilisent du GaN comme couches barrières. Cependant, notre objectif a été de faire croître des MQW à contenu élevé avec des barrières InGaN sur une nouvelle template InGaN appelé «semi-bulk» (SB). La réalisation de la thèse est de simuler, décroître par épitaxie en phase vapeur organométallique (MOVPE) et de fabriquer la structure de DELs à haute teneur en In dans les barrières MQW avec InGaN, crues sur une template InGaN «semi-bulk» de haute qualité, et qui émettent dans le spectre du bleu au vertGaN-based light-emitting diodes (LEDs) have already been commercialized for solid-state lighting, since the InGaN/GaN-based multi-quantum-well (MQW) of LEDs can be designed to produce light in the entire visible spectral range. To obtain white LED, phosphor-based down-conversion results in low efficiency due to Stokes loss and also can yield low colour rendering index (CRI). Hence, for highly efficient and with high CRI white light, generation of white light by monolithic red-green-blue (RGB) combination is necessary. InGaN/GaN-based blue LED has good performance now-a-days. III-phosphides based red LED has also achieved good efficiency. However, with intermediary wavelengths for green spectra emission, the efficiency of devices from epitaxy grown along the commonly used (0001-Ga) direction of GaN decreases with increasing indium (In) content in the active region and this “green-gap” is the main obstacle to get phosphor-free white LEDs. Non- or semi-polar LED structures could be a solution to reduce or omit the polarization problem, however, easier growth of good crystal quality and fewer processing steps make (0001-Ga) direction growth still commercially promising. Therefore, optimized structure design to alleviate polarization and enhance optical emission from hetero-structures grown along this direction growth is still in demand. The conventional InGaN multi-quantum-well (MQW) LED structures are grown on GaN buffer and use GaN as barrier layers. However, the objective of this thesis has been to grow high In-content MQWs with InGaN barriers on a novel so called “semi-bulk” (SB) InGaN buffer. The achievement of the thesis was to simulate, grow by metalorganic vapour phase epitaxy (MOVPE) and process LED structure with high In-content in the MQW with InGaN barriers, grown on high quality “semi-bulk” InGaN buffer, that will emit in the blue to green spectra. 70 nm thick high crystal quality InGaN SB buffer was obtained with 5% In-content. On top of this, In0.15Ga0.85N/In0.05Ga0.95N MQW was grown followed by 200 nm optimized p-GaN. The room temperature IQE was 67.5% at 460 nm emission wavelength. The processed LED chips yielded turn-on voltage less than 3 V with leakage current of ~10-3 A. In0.25Ga0.75N/ In0.05Ga0.95N MQW was also realized on InGaN SB with 7% In, with emission peak at ~530 nm
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Danhof, Julia [Verfasser], and Ulrich T. [Akademischer Betreuer] Schwarz. "Local charge carrier diffusion and recombination in InGaN quantum wells = Lokale Ladungsträgerdiffusion und -rekombination in InGaN Quantentrögen." Freiburg : Universität, 2013. http://d-nb.info/1123477663/34.
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Malinauskas, Tadas. "Krūvininkų dinamikos tyrimas plačiatarpiuose puslaidininkiuose šviesa indukuotų dinaminių gardelių metodu." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091215_091639-56509.
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Disertacijoje pristatomi didelio krūvininkų tankio dinamikos tyrimai skirtingo defektiškumo GaN, InGaN bei deimanto sluoksniuose atlikti naudojant šviesa indukuotų dinaminių gardelių metodą. Naudojant eksperimentinius rezultatus gautus skirtingo žadinimo intensyvumo, temperatūros sąlygomis bei pasitelkus skaitmeninį krūvininkų dinamikos modeliavimą nustatomi dominuojantys krūvininkų rekombinacijos bei sklaidos mechanizmai tirtuose plačiatarpiuose puslaidininkiuose. Parodoma, kad dislokacijų sąlygota nespindulinė rekombinacija dominuoja GaN bandiniuose su dislokacijų tankiu didesniu nei 1E8 cm-2, esant mažesniems dislokacijų tankiams krūvininkų gyvavimo trukmę lemia bimolekulinė rekombinacija. Nustatyta, kad eksperimentiškai stebėtas krūvininkų difuzijos koeficiento didėjimas GaN yra sukeltas Fermi slėgio išsigimusioje krūvininkų plazmoje. Krūvininkų rekombinacijos trukmių bei azoto priemaišų kiekio koreliacija sintiniuose deimantuose parodė, kad su azotu susietos priemaišos yra pagrindiniai rekombinacijos centrai Tai pat darbe pristatoma nauja šviesa indukuotų dinaminių gardelių eksperimento schema su holografiniu pluoštelio dalikliu, leidžianti supaprastinti eksperimentą bei įgalinanti heterodininį difrakcijos signalo detektavimą. Parodoma, kad fazės skirtumas tarp signalo ir foninės šviesos gali būti kontroliuojamas keičiant holografinio daliklio padėtį išilgai jo gardelės vektoriaus krypties.The investigation of high density carrier dynamics in GaN, InGaN, and diamond samples with different defect density by light induced transient grating technique is presented in the thesis. The experimental studies on numerous samples, grown at different conditions, combined with extensive measurements in a wide range of carrier densities (1E16-1E20 cm-3) and temperature (9-300K) is used to identify the interplay of radiative and nonradiative recombination mechanisms, to determine carrier lifetime, diffusion coefficient, and diffusion length. It is shown that dislocation governed carrier recombination is a dominant recombination channel in GaN samples with dislocation density above 1E8 cm-2, otherwise, the bimolecular recombination dominates at high carrier densities. Experimentally observed increase of carrier diffusivity in GaN is caused by Fermi pressure at degenerate carrier plasma. The correlation between the carrier lifetime and concentration of nitrogen defects points out that nitrogen-related defects act as the main centers of nonradiative recombination in synthetic diamonds. A novel heterodyne detection scheme for LITG technique is presented. The heterodyning is achieved by coherently mixing the picosecond pulses of diffracted and scattered light. It is shown that a phase difference between theses fields can be controlled by moving holographic beam splitter along its grating vector.
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Malinauskas, Tadas. "Investigation of carrier dynamics in wide bandgap semiconductors by light-induced transient grating technique." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091215_091652-19632.
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III-nitrides, diamonds are extremely promising wide band gap semiconductor materials for optoelectronics and high temperature, high power electronics. Therefore, there is huge scientific interest in investigation electrical and optical properties of these materials. The light induced transient grating technique (LITG) is very suitable for exploration of carrier dynamics which governed by fundamental and defect related properties of materials.
The main goals of the thesis were gain a new knowledge on carrier dynamics in wide bandgap semiconductors (namely GaN, InGaN, and diamonds) by using and developing light induced transient grating technique. The experimental studies on numerous samples, grown at different conditions, combined with extensive measurements in a wide range of carrier densities (1016-1020 cm-3) and temperature (9-300K) was targeted to identify the interplay of radiative an nonradiative recombination mechanisms, to determine carrier lifetime dependence on the excess carrier density, to explain the carrier diffusion coefficient dependence on excitation intensity, to find the optimal materials growth conditions.
A novel heterodyne detection scheme for LITG technique was presented. The heterodyning was achieved by coherently mixing the picosecond pulses of diffracted and scattered light. A phase difference between theses fields was controlled by moving holographic beam splitter (HBS) along its grating vector. LITG signal decay kinetics, recorded at two HBS... [to full text]III grupės nitridai bei deimantai tai platų draustinės energijos tarpą turintys puslaidininkiai, pasižymintys unikaliomis medžiagos savybėmis ir turintys didelį potencialą aukštų temperatūrų, didelių galių, opto/elektroniniams taikymams. Todėl šių medžiagų elektrinės bei optinės savybės pastaruoju metu yra intensyviai tiriamos. Šviesa indukuotų dinaminių gardelių (ŠIDG) metodas labai tinka tyrinėti krūvininkų dinamiką, kuri yra nulemta fundamentinių bei defektinių medžiagos savybių. Pagrindiniai darbo tikslai buvo gauti naujų žinių apie krūvininkų dinamiką plačiatarpiuose puslaidininkiuose (GaN, InGaN bei deimantuose) naudojat bei plėtojant šviesa indukuotų gardelių metodiką. Ištirti didelio nepusiausvirųjų krūvininkų tankio rekombinacijos ir difuzijos ypatumus skirtingo defektiškumo GaN, InGaN sluoksniuose bei sintetiniuose deimantuose. Skaitmeniškai modeliuojant krūvininkų dinamiką nustatyti dominuojančius krūvininkų rekombinacijos mechanizmus bei krūvininkų gyvavimo trukmes, difuzijos koeficientus ir nuotolius. Darbe pristatoma nauja ŠIDG eksperimento schema su holografiniu pluoštelio dalikliu, leidžianti supaprastinti eksperimentą. Ši schema taip pat įgalino heterodininį difrakcijos signalo detektavimą. Parodoma, kad fazės skirtumas tarp signalo ir foninės šviesos gali būti kontroliuojamas keičiant holografinio daliklio padėtį išilgai jo gardelės vektoriaus krypties. Ištyrus didelį kiekį GaN sluoksnių, užaugintų skirtingomis technologijomis bei pasižyminčiu skirtingu... [toliau žr. visą tekstą]
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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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Bartel, Til Pierre. "Optische Eigenschaften von Exzitonen in InGaN-Quantenstrukturen." Berlin : Univ.-Verl. der TU, Univ.-Bibliothek, 2004. http://d-nb.info/988216752/34.
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Brown, Iain. "Internal field effects in InGaN quantum wells." Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/55968/.
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InGaN/GaN based quantum well structures are strained and due to the lack of a centre of symmetry large internal fields are present which skew the potential of the quantum wells, this has a large effect on the properties of these structures. InGaN/GaN based quantum well structures are studied using a theoretical method based on the Pade model and comparison made with experimental results. The importance of using a correct description for the depletion widths of p-i-n structures for use in interpreting measurements of the internal field is established in this work. Interpreting the results from reverse bias photocurrent absorption measurements of an In0.1Gao.9N quantum well structure, a value of-1.9 MVcm-1 for the internal field has been determined, which is within 5 % of the field of -1.8 MVcm-1 calculated using piezoelectric constants interpolated from the binaries. Comparison of the results of the Pade model and experiment demonstrate that the experimental absorption magnitude is an unreliable indication of the internal field due to the carrier extraction efficiency at low bias, hence the absorption peak energy should be used. Using a theoretical model governed by pumping and recombination processes time-resolved photoluminescence experiments performed at Sheffield University have been modelled. It was found that the observed shift of the emission peak arises from a delicate balance between the contributions from bandgap renormalisation, screening of the internal field and the Coulomb interaction. Comparisons between the free carrier and Pade models, found that the energy shift and magnitude of the peak intensity are underestimated when using the free carrier model. Although the internal field is strongly screened at high carrier density, the increase in the dipole matrix element is small. It was found that at threshold the screened internal field is still of the order of -1 MVcm-1, hence inclusion of the screened internal field is essential in laser gain-current calculation.
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Sharma, Nikhil. "Characterisation of InGaN/GaN light emitting diodes." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621315.
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Watson-Parris, Duncan Thomas Stephens. "Carrier localization in InGaN/GaN quantum wells." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/carrier-localization-in-ingangan-quantum-wells(d1f06539-6fde-4ec4-beac-31689a571804).html.
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Presented in this thesis are extensive theoretical investigations into the causes and effects of carrier localization in InGaN/GaN quantum wells. The results of the calculations agree well with experimental data, where it is available, and provide additional insights into the mechanisms that lead to some of the experimentally observed effects of localization. Firstly, the wave functions of the electrons and holes in InGaN/GaN quantum wells have been calculated by numerical solution of the effective-mass Schrödinger equation. In our calculations we have assumed a random distribution of indium atoms, as suggested by the results of atom probe tomography: this allows us to find the contributions to the carriers' potential energy that arise from band gap fluctuations, the deformation potential and the spontaneous and piezoelectric fields. We show that the fluctuations in alloy composition can be sufficient to localize the carriers; our results are in good agreement with the results of experiment and more detailed ab-initio calculations, but we also obtain information about the distribution of localized states which those methods cannot yet provide. We find that the holes are localized on a short scale in randomly-occurring regions of high indium content, whereas the electrons are localized on a longer length scale. We consider the effect of well width fluctuations and find that these contribute to electron localization, but not to hole localization. We also simulate the low-temperature photoluminescence spectrum and find good agreement with experiment for the energy, width and shape of the photoluminescence peak. Secondly, we have used first-order time-dependent perturbation theory to study the diffusion of the carriers between their localized states at non-zero temperatures. The rates for scattering via the interaction with acoustic phonons are calculated using the carrier wave functions, and the resulting master equation for the distribution of the carriers is solved by a Monte Carlo method. We find that, even towards room temperature, the carriers are localized to a small number of states, and that their diffusion lengths are proportional to a combination of the density of localized states and the localization length. The experimentally-observed `S-shape' of the photoluminescence peak energy as a function of temperature is reproduced in our results and is explained by the thermal redistribution of holes among the localized states. A reduction of the depth of this S-shape is found as the excitation power is increased, as has been observed experimentally, and which we attribute to the saturation of the localized states.
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Dogmus, Ezgi. "Characterization and fabrication of InGaN solar cells." Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10123/document.
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Ce projet a pour ambition de concevoir et de réaliser une nouvelle filière de cellule photovoltaïque utilisant la conversion directe de l’énergie solaire en électricité à base de la filière InGaN permettant d'atteindre un rendement de 50% de conversion directe de l’énergie solaire en électricité. Cette nouvelle approche constitue un défi technologique majeur pour la recherche académique et les applications industrielles dans les années avenir. Les cellules solaires actuelles à base de Silicium approchent leur limite théorique de rendement de conversion d’énergie (environ 25%). Les cellules solaires multi-jonctions permettent de repousser ces limites en empilant plusieurs matériaux possédant différentes énergies de bande interdite, chacun absorbant une petite portion du spectre solaire de manière plus efficace. Alors que les LEDs violettes et bleu à base du matériau InGaN sont déjà commercialisées, il apparaît essentiel de relever le défi qui consiste à fabriquer et utiliser ce matériau InGaN avec de fort taux d’Indium (i.e. des énergies de bandes interdites plus faibles) afin de couvrir l’ensemble du spectre solaire et ainsi réaliser des cellules photovoltaïques à très haut rendement, bien au-delà de l’état de l’art international. Au vu des limitations des cellules au silicium, des travaux théoriques ont montrés que des cellules à jonctions multiples à base de couches absorbantes d’InGaN permettraient d’atteindre un rendement de 50%. L’amélioration du rendement des cellules solaires aura un impact majeur sur de nombreuses applications. L’objectif de ce travail concerne la conception et de réalisation d'une nouvelle génération de cellule solaire à base d’InGaN. Ce travail concerne dans une première phase : la caractérisation du matériau InGaN à fort taux d’Indium (> 20%) élaboré à l'EPFL en collaboration avec l'IEMN ayant pour but de démontrer une énergie de bande interdite en dessous de 2 eV. Dans une seconde phase, après la validation électrique et structurelle de ce nouveau matériau, il s’agit de concevoir et de réaliser une nouvelle génération de cellule solaire mono-jonction sur saphir et sur substrat GaN. Cette nouvelle cellule solaire pourra être intégrée au sein d’une microsource d’énergie pour réseau de capteur autonomeThis PhD thesis reports on the structural and optical characterization of solar cell structures with various active region designs and different substrates as well as the subsequent fabrication and electrical characterization of InGaN solar cells. The epitaxial growth of solar cell designs with pGaN/i-InGaN/n-GaN structures were performed by metal-organic vapor phase epitaxy (MOCVD) by the company NovaGaN. The structural and optical characterization is assessed by X-Ray diffraction, scanning transmission electron microscopy, atomic force microscopy and photoluminescence spectroscopy. A structural comparison of solar cell designs including bulk 200 nm thick InGaN layer and InGaN/GaN multiple quantum wells (MQWs) with similar indium compositions (~30%) is presented. Furthermore, structural quality of designs with InGaN/GaN MQWs were analyzed with variation of the indium content, thickness of InGaN quantum wells and type of the substrate, i.e. (0001) sapphire or bulk GaN substrate. An optimized and reproducible processing has been developed for fabrication of InGaN based solar cells. The challenges in device processing such as mesa etching of GaN and contamination on the device sidewalls, which caused high reverse leakage currents were studied and solutions of using SiO2 mask and protection of sidewalls by SiO2 layers were proposed. An optimization study of thermal treatment of Ni/Au current spreading layer is also presented. The electrical activity in the active region and the spectral response of the solar cells are investigated by electron beam induced current (EBIC) analysis and external quantum efficiency measurements. EBIC analysis is used to clarify the origin of the S-shape behavior in illuminated current-voltage characteristics of the solar cell with 25×In0.15Ga0.85N/GaN MQWs, which has performed the best performance in this study with a conversion efficiency of 0.59% under 1sun illumination (AM1.5G)
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Morassi, Martina. "Croissance de nanofils InGaN pour les dispositifs de récupération d’énergie photovoltaïques et piézoélectriques." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS249.
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Les matériaux III-nitrures sont des excellents semi-conducteurs qui présentent plusieurs propriétés intéressantes pour les applications photovoltaïques et piézoélectriques. Au même temps, la croissance epitaxiale de ces matériaux sous forme de nanofil (NF) est de tant en plus intéressant, car les NFs nitrures binaires et heterostructurés, ont une qualité cristalline supérieure comparés aux homologues 2D et massifs. Dans ces contextes, ce travail est axé sur la croissance par MBE assistée par plasma (PA-MBE) de NFs InGaN/GaN et leur caractérisation. Trois sujets principaux ont été abordés: l'étude de la croissance d’heterostructures InGaN axiales par PA-MBE, leur caractérisation optique, et l'étude de la croissance sélective de NFs GaN sur graphène transféré. Ces études m’ont permis d’obtenir un control rational sur le mode de croissance d’heterostructures InGaN dans une large gamme de teneurs d’In (jusqu'à ~ 40%) et morphologies, de étudier leur structure de bande axiale, utile pour la conception optimale de la structure p-i-n photovoltaïque, et de démontrer pour le première fois dans la littérature, que l’épitaxie sélective de NFs de GaN sur MCG lithographié est une route possible et très promettent pour améliorer leur homogénéité. Ainsi, des tests préliminaires ont montré que la capacité de piézo-conversion des NFs GaN peut être améliorée d'environ 35% lors de l'intégration d’une insertion InGaN riche en In dans leur volume.Tous ces résultats constituent un ’étape décisive dans le contrôle et la comprension des propriétés de ces nanostructures, et donnent des perspectives très encourageantes pour leur intégrations dans des nano-générateurs à haute efficacitéIII-nitride materials are excellent semiconductors presenting several interesting properties for photovoltaic and piezoelectric applications. At the same time, the epitaxial growth of these materials in the form of nanowires (NW) is even more interesting, because binary and heterostructured III-N NWs have a higher crystalline quality compared to the 2D and bulk counterparts. In these contexts, this work focuses on the plasma-assisted MBE (PA-MBE) growth of InGaN / GaN NWs and their characterization. Three main topics are addressed: the growth of axial InGaN heterostructures by PA-MBE, their optical characterization, and the study of the selective area growth (SAG) of GaN NWs on transferred graphene. These studies allowed me to obtain a rational control on the growth mode of InGaN heterostructures in a wide range of In contents (up to ~ 40%) and morphologies, to study their axial band edge profile, useful for the optimal design of the photovoltaic structure, and to demonstrate for the first time in the literature, that the SAG of GaN NWs on patterned mono-layer graphene is a possible and very promising strategy to improve their homogeneity. Also, preliminary tests have shown that the piezoelectric conversion capacity of GaN NWs can be improved by about 35% when integrating an In-rich InGaN insertion into their volume.All these results constitute a decisive step in the control and the comprehension of the properties of these nanostructures, and establish very encouraging perspectives for their integration in novel and efficient photovoltaic and piezoelectric nano-generators
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Jarjour, Anas F. "Optical Studies of Single InGaN/GaN Quantum Dots." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491621.
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Experimental investigation of the optical properties of single InGaN/GaN quantum dots (QDs) is presented. The results are compared to a theoretical model based on an atomistic semi-empirical tightbinding approach. Nonlinear excitation is investigated by micro-photoluminescence (micro-PL), time-resolved PL and PL excitation (PLE) spectroscopy. It is found to produce almost total suppression of the background emission arising from the underlying quantum well. This is explained qualitatively by the enhancement of the nonlinear absorption due to the zero-dimensional confinement in the QDs. PLE spectra show clear evidence for the existence of excited states. We present direct evidence of the control of the oscillator strength of the exciton state in the QD by an applied vertical electric field. This is achieved through the study of the radiative lifetime of the QD embedded in a p-i-ll diode structure. The effect is explained by the increase in the overlap between the electron and the hole wavefunctions due to the partial compensation of the internal piezoelectric field and was found to be accompanied by a large blue shift of the transition energy. The results are found to be in good quantitative agreement with theoretical predictions arising from the theoretical model extended to take into account the effect of the applied field. The induced increase in the overlap between the wavefunctions of the carriers is shown experimentally to enhance the attractive Coulomb interaction leading to the change of the sign of the biexcitonic binding energy. The electroluminescence observed from the structure under forward bias showed clear indication of single QD emission which persists up to ',,85 K. The generation of single photons in the blue spectral region from a single QD is demonstrated. The collection efficiency was enhanced by embedding the QD layer in a low-Q microcavity. The single QD emission is observed to be ',,10 times stronger than typical emission without a cavity. Nonlinear excitation spectroscopy proved essential in these measurements since any background emission would mask the signature of single-photon emission. This result provides a clear evidence of the quantum nature of the emission.
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Soundararajah, Queenie Yoganandhi. "Characterization of InGaN nanorods using transmission electron microscopy." Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720816.
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Li, Zonglin, and 李宗林. "Reliability study of InGaN/GaN light-emitting diode." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43224155.
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Mandl, Martin [Verfasser]. "Dreidimensionale InGaN Leuchtdioden: Epitaxie, Prozessierung, Charakterisierung / Martin Mandl." München : Verlag Dr. Hut, 2017. http://d-nb.info/1126298026/34.
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Eshghi, Hosein. "Electron and hole transport in GaN and InGaN." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/2237/.
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Lynch, Richard James. "Investigation into the spectral linewidth of InGaN LEDs." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420843.
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Christian, George. "Photoluminescence studies of InGaN/GaN quantum well structures." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/photoluminescence-studies-of-ingangan-quantum-well-structures(aa935835-26f3-4b12-8f83-21190ffa7cb9).html.
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In this thesis, optical studies of c-plane InGaN/GaN quantum well (QW) structures are presented. The effects of a Si-doped underlayer (UL) on the optical properties of multiple quantum well (MQW) structures are investigated. The QW photoluminescence (PL) emission peak energy and radiative recombination rate decrease and increase respectively with increasing number of QWs. These observations are attributed to the increasing net electric field across the MQW structure as the strength of the surface polarisation field, which acts in the opposite sense to the piezoelectric polarisation fields across the QWs, reduces with increasing distance of the UL from the sample surface. This leads to a reduction in the electron-hole recombination energy and wavefunction overlap. It is also shown that the internal quantum efficiency of the MQW structures may decrease with increasing number of QWs due to the reducing radiative recombination rate, which could indicate that carrier losses due to thermionic emission or interface recombination are mitigated by the inclusion of an UL. Optical studies of single QW structures containing Si-doped ULs with different net electric fields across the QW are presented. The net electric field across the QW is changed by varying the thickness of the GaN cap layer. The full width at half maximum of the emission peak increases with increasing net electric field across the QW. This is attributed to the increasing variation in electron ground state energies due to the role of the electric field in the localisation of electrons at quantum well width fluctuations. For one sample, a smaller Huang-Rhys factor compared to the rest of the samples is calculated. The non-exponential PL decays detected on the low energy side of the QW emission peak from this sample are also of a different shape to the other PL decays detected at all energies for the other samples. This may be due to the reversal of the net electric field across these QW regions. Observations of a broad emission band on the high energy side of single QW structures at high excited carrier densities are presented. This band occurs in the carrier density regime at which the efficiency droop is observed. The emission band is attributed to higher energy weakly localised or delocalised electron and hole states that are populated following the saturation of the localised ground states. PL decay curves detected across this emission band exhibit plateaus where the PL intensity remains constant until the higher energy emission has decayed. These are similar to decays observed in semiconductor quantum dots, which are characteristic of Pauli state blocking.
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Fox, Sophia. "Computational electromagnetic modelling of InGaN/GaN nano-LEDs." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760895.
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This work focuses on the development for the electromagnetic optical modellingof a commercial III-nitride vertical LED/nano-LED based on the finite-differencetime-domain (FDTD) method. The material properties, boundary conditions andsource emission are thoroughly investigated. To achieve a reliable model, results obtained from FDTD using a near-to-far-field transform are compared with those obtained using experimental angular photoluminescence (PL). LED parameters are extracted to quantify the performance of the devices and predict the emission pattern of practically infeasible nanorod arrays on vertical LED structures. It is demonstrated the impact of the shape and dimensions of the nanorods has a significant impact on the light extraction efficiency, however further optimisation is required to significantly increase directionality.
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Girgel, Ionut. "Development of InGaN/GaN core-shell light emitters." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720648.
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Gallium nitride (GaN) and its related semiconductor alloys are attracting tremendous interest for their wide range of applications in blue and green LEDs, diode lasers, high-temperature and high-power electronics. Nanomaterials such as InGaN/GaN core-shell three-dimensional nanostructures are seen as a breakthrough technology for future solid-state lighting and nano-electronics devices. In a core-shell LED, the active semiconductor layers grown around a GaN core enable control over a wide range of wavelengths and applications. In this thesis the capability for the heteroepitaxial growth of a proof-of-principle core-shell LED is advanced. A design that can be applied at the wafer scale using metalorganic vapor phase epitaxy (MOVPE) crystal growth on highly uniform GaN nanorod (NR) structures is proposed. This project demonstrates understanding over the growth constraints of active layers and dopant layers. The impact of reactor pressure and temperature on the morphology and on the incorporated InN mole fraction was studied for thick InGaN shells on the different GaN crystal facets. Mg doping and effectiveness of the p-n junction for a core-shell structure was studied by extensive growth experiments and characterization. Sapphire and Si substrates were used, and at all the stages of growth and fabrication. The structures were optimized to achieve geometry homogeneity, high-aspect-ratio, incorporation homogeneity for InN and Mg dopant. The three-dimensional nature of NRs and their light emission provided ample challenges which required adaptation of characterization and fabrication techniques for a core-shell device. Finally, an electrically contacted core-shell LED is demonstrated and characterized. Achieving a proof-of-principle core-shell device could be the starting point in the development of nanostructure-based devices and new physics, or in solving technical problems in planar LEDs, such as the polarization of emitted light, the quantum-confined Stark effect, efficiency droop, or the green gap.
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Kapoor, Akanksha. "Core-shell InGaN/GaN wires for flexible LEDs." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALY013.
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Les hétérostructures planaires à base de puits quantiques InGaN/GaN sont désormais largement utilisées dans les diodes électroluminescentes (LED). Les LED bleues et les LED blanches à phosphores sont largement commercialisées avec des rendements d’émission de lumière très élevés. Néanmoins, il reste encore des problèmes à résoudre avec ce type de dispositifs : l’émission à plus grande longueur d'onde (rouge) avec de bonnes efficacités, le problème du la chute du rendement à forte puissance (« droop efficiency ») et l’amélioration de l’extraction de la lumière. Ce travail de thèse présente l'utilisation de fils GaN ayant une hétérostructure radiale InGaN/GaN qui peut s’avérer un choix intéressant pour le développement de nouvelles LED visibles grâce à plusieurs avantages-clés : un encombrement réduit, un rapport d'aspect élevé et une grande qualité cristalline avec de faible densité de défauts. Les fils permettent également de fabriquer des LED flexibles intéressantes pour de nouvelles applications comme les écrans enroulables, les dispositifs médicaux de petite taille et flexibles, etc. Ce travail est consacré à une étude complète qui part de la croissance auto-assemblée de fils à hétérostructures InGaN/GaN radiale plan-m par la méthode d’épitaxie en phase vapeur d’organiques métalliques, jusqu’à l’intégration des fils dans des dispositifs flexibles, en étudiant en particulier des hétérostructures émettant dans le vert. L'influence d'une sous-couche InGaN et d'un espaceur GaN est spécifiquement étudiée pour améliorer l'efficacité d’émission d'un puits quantique (PQ) unique émettant dans le bleu. On constate que la présence de l’espaceur GaN est nécessaire pour obtenir une émission efficace du PQ dans le plan-m des fils de GaN, alors qu'aucun changement n'est observé en ajoutant une sous-couche d’InGaN. De plus, des LED flexibles avec différentes longueurs d'onde telles que l'émission bleue, verte et bicolore ont été réalisées en ajustant la teneur en indium à l'intérieur des hétérostructures à puits quantiques InGaN/GaN. Cette étude approfondie corrèlent les propriétés structurelles, optiques et électriques. L'utilisation de la croissance sélective est également abordée pour essayer d’améliorer les performances des LED flexibles à nanofils mais la maitrise de la reproductibilité reste difficile à contrôler. Pour obtenir un dispositif LED flexible émettant une lumière blanche, une étude d'optimisation des phosphores combinés à la LED bleue a également été réaliséeThe InGaN/GaN-based planar heterostructures are now widely used to produce light emitting diodes (LEDs). The blue LEDs and phosphor-converted white LEDs are already commercialized with high efficiencies. But further scope to reach long wavelength emission with improved efficiencies and mitigating issues likes efficiency droop and poor light extraction still remains. This Ph.D. thesis presents the use of core-shell InGaN/GaN wires as an attractive choice for visible LEDs thanks to their smaller footprint, high aspect ratio and low defect density. The bendable wires also allow fabricating LEDs with flexibility in view of rapidly growing demands for rollable displays, wearable devices, flexible biomedical instruments, etc. This work focuses on a complete study, beginning from the self-assembled growth of m-plane core-shell InGaN/GaN wires by metal organic vapor phase epitaxy to their integration in working devices on flexible substrates, especially on original green-emitting heterostructures. The influence of an InGaN under layer (UL) and GaN-spacer is investigated to improve the efficiency of a blue single quantum well. It is found that the presence of a GaN spacer is required to achieve efficient m-plane emission from core-shell wires, while no internal quantum efficiency change is observed by adding an InGaN UL. Further, flexible LEDs with different wavelengths such as blue, green and dual-color emission have been realized by tuning the indium content inside InGaN/GaN multiple quantum well heterostructures followed by a comprehensive study correlating structural, optical and electrical properties. The use of selective area growth is also approached to address the issues encountered in device emission and remaining challenges in the reproducibility control are discussed. To target white light emission, an optimization study of yellow phosphors combined with the well-established blue LED has also been performed
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Mahat, Meg Bahadur. "Ultrafast Spectroscopy of Hybrid Ingan/gan Quantum Wells." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc149635/.
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Group III nitrides are efficient light emitters. The modification of internal optoelectronic properties of these materials due to strain, external or internal electric field are an area of interest. Insertion of metal nanoparticles (MNPs) (Ag, Au etc) inside the V-shaped inverted hexagonal pits (IHP) of InGaN/GaN quantum wells (QWs) offers the potential of improving the light emission efficiencies. We have observed redshift and blueshift due to the Au MNPs and Ag MNPs respectively. This shift could be due to the electric field created by the MNPs through electrostatic image charge. We have studied the ultrafast carrier dynamics of carriers in hybrid InGaN/GaN QWs. The change in quantum confinement stark effect due to MNPs plays an important role for slow and fast carrier dynamics. We have also observed the image charge effect on the ultrafast differential transmission measurement due to the MNPs. We have studied the non-linear absorption spectroscopy of these materials. The QWs behave as a discharging of a nanocapacitor for the screening of the piezoelectric field due to the photo-excited carriers. We have separated out screening and excitonic bleaching components from the main differential absorption spectra of InGaN/GaN QWs.
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Davies, Matthew John. "Optical studies of InGaN/GaN quantum well structures." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/optical-studies-of-ingangan-quantum-well-structures(f6c6e59b-8366-44aa-b149-9338d3f03dc0).html.
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In this thesis I present and discuss the results of optical spectroscopy performed on InGaN/GaN single and multiple quantum well (QW) structures. I report on the optical properties of InGaN/GaN single and multiple QW structures, measured at high excitation power densities. I show a correlation exists between the reduction in PL efficiency at high excitation power densities, the phenomenon so-called ``efficiency-droop'', and a broadening of the PL spectra. I also show a distinct change in recombination dynamics, measured by time-resolved photoluminescence (PL), which occurs at the excitation power densities for which efficiency droop is measured. The broadening of the PL spectra at high excitation power densities is shown to occur due to a rapidly redshifting, short-lived high energy emission band. The high energy emission band is proposed to be due to the recombination of weakly localised/delocalised carriers occurring as a consequence of the progressive saturation of the local potential fluctuations responsible for carrier localisation, at high excitation power densities. I report on the effects of varying threading dislocation (TD) density on the optical properties of InGaN/GaN multiple QW structures. No systematic relationship exists between the room temperature internal quantum efficiency (IQE) and the TD density, in a series of nominally identical InGaN/GaN multiple QWs deposited on GaN templates of varying TD density. I also show the excitation power density dependence of the PL efficiency, at room temperatures, is unaffected for variation in the TD density between 2 x107 and 5 x109 cm-2. The independence of the optical properties to TD density is proposed to be a consequence of the strong carrier localisation, and hence short carrier diffusion lengths. I report on the effects of including an InGaN underlayer on the optical and microstructural properties of InGaN/GaN multiple QW structures. I show an increase in the room temperature IQE occurs for the structure containing the InGaN underlayer, compared to the reference. I show using PL excitation spectroscopy that an additional carrier transfer and recombination process occurs on the high energy side of the PL spectrum associated with the InGaN underlayer. Using PL decay time measurements I show the additional recombination process for carriers excited in the underlayer occurs on a faster timescale than the recombination at the peak of the PL spectrum. The additional contribution to the spectrum from the faster recombination process is proposed as responsible for the increase in room temperature IQE.
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Li, Zonglin. "Reliability study of InGaN/GaN light-emitting diode." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43224155.
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Tamiazzo, Gianluca. "Loss Mechanisms in InGaN/GaN Quantum Well Structures." Doctoral thesis, Università degli studi di Padova, 2008. http://hdl.handle.net/11577/3425068.
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The study of the electro-optical properties of semiconductors has represented one of the major topics in the research of physicists and material scientists of the last century. Extensive efforts have been especially put in the last four decades into the search for materials emitting in the visible region, with the aim of developing Light Emitting Diodes (LEDs) for general outdoor lighting as well as for new applications, where micro-size and device integration are necessary requirements.
GaN/InGaN/AlGaN-based LEDs lead nowadays the solid-state lighting market, which is in continuous expansion and finds always new applications, such as display back-lighting and projection, full color displays and automotive lighting. Due to the increasing market competitiveness, further improvement of LED brightness and long term reliability, together with the reduction of production costs, are of primary concern for each LED supplier. The enhancement of device effciency and reliability requires the understanding of the physics of these devices and the optimization of the LED design.
Despite of the high long-term stability reached, degradation mechanisms could still potentially occur. In this work, loss mechanism causing aging are investigated for GaN-based LEDs. Operation-induced degradation of high-brightness LEDs internal quantum e’±ciency is analyzed both experimentally and theoretically. The dynamics of the aging process are studied by means of electroluminescence relative intensity
measurements in dependence of time. A model able to interpret this behavior is proposed. In particular, a thermally activated mechanism, likely correspondent to the p-type-dopant diffusion process, is believed to be responsible for long-term DC aging.
In section 1, properties of Gallium Nitride material are analyzed in detail. Growing and doping methods, employed substrates and fabrication of contacts are briefly described. A description of related GaN alloys is then given. Information wrapped in this chapter will be frequently mentioned in the entire work.
In section 2, an overview of the Light Emitting Diode structure is given. Topics as radiative recombination theory, non radiative recombination mechanisms and LED theory basics are examined. Finally, recently developed LED improvement techniques are shortly described.
In section 3, LED degradation theory is analyzed. Principal degradation modes are first briefly traced. Then, samples used in this study are described together with measuring methods and general dynamics of aging. Acceleration concept isfinally depicted.
In section 4, a new model based on dopant diffusion is developed. The model is able to interpret most of the degradation phenomena experimentally encountered and gives a first complete description of GaN/InGaN/AlGaN-based LEDs aging. A general introduction to diffusion theory is first given, together with literature results. The model is then mathematically described. An experimental application explaining temperature dependence of LED samples is presented. Finally, the model is developed from a physical point of view, and a derivation of the acceleration factor is given.
In section 5, a description of an experiment based on EL and PL analysis over double and multi quantum well structures is given. The aim of the experiment is to monitor the behavior of a single QW in terms of effciency and reliability in dependence of its positioning.
In section 6, current density impact over the structures is analyzed. The diffusion model is systematically applied to find experimental indications to the effects of a current over-stress on GaN-based LEDs. The current-induced phenomena are reduced to simple thermal degradation.
In section 7, LED aging characteristics are monitored in dependence of device wavelength. A set of samples emitting at different wavelengths is compared in terms of aging properties.
In section 8, some diffusion evidences are considered. Diffusion is proved to be actual already during sample growth. Moreover, defect density impact is taken into consideration, in particular related to the initial aging phase. Finally, a theoretical interpretation is given for a contactless case of degradation named photoaging.
Results of the study are summarized in the last section.
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Dobrovolskas, Darius. "Krūvininkų dinamikos InGaN tyrimas liuminescencijos su erdvine skyra metodais." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2013~D_20131202_131541-88572.
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Disertacija yra skirta krūvininkų lokalizacijos ir rekombinacijos tyrimams InGaN epitaksiniuose sluoksniuose ir dariniuose panaudojant fotoliuminescencinę spektroskopiją su submikrometrine erdvine skyra. Optinius bandinių tyrimus papildo struktūrinė analizė. Darbe parodyta, jog relaksavusiuose InGaN sluoksniuose egzistuoja į nanokolonas panašūs dariniai, kurie papildomai prisideda prie netolygaus fotoliuminescencijos pasiskirstymo InGaN epitaksiniuose sluoksniuose. Pademonstruota galimybė nuslopinti priemaišinės kilmės liuminescenciją InGaN sluoksnyje jį iškaitinus lazerio spinduliuote. Atskleistas netyčinis InGaN darinių aktyviojo sluoksnio iškaitinimas, vykstantis formuojant p tipo sluoksnius, kuris keičia InGaN kvantinių darinių optines sąvybes. Išnagrinėta neigiama koreliacja tarp fotoliuminescencijos intensyvumo ir juostos viršūnės bangos ilgio InGaN kvantiniuose dariniuose ir pasiūlytas naujas šios ypatybės interpretavimo modelis. Lokaliai stebėtas liuminescencijos intensyvumo padidėjimas dėl sąveikos su lokalizuotais paviršiniais plazmonais, indukuotais sidabro nanodalelėse. Parodytas potencialo fliuktuacijų daromas poveikis rezonansinei sąveikai tarp optinių dipolių kvantinėse duobėse ir lokalizuotų paviršinių plazmonų.The thesis is aimed at gaining new knowledge on carrier localization and recombination in InGaN epilayers and structures by using photoluminescence spectroscopy with sub-micrometer spatial resolution. Optical characterization is combined with the structural analysis to provide a deeper insight into peculiarities of InGaN luminescence. Studies of InGaN epitaxial layers showed the relaxed layers to contain nanocolumn-like structures that additionally contribute to inhomogeneous photoluminescence distribution in InGaN layers. The feasibility of suppressing the defect-related emission in InGaN epilayers by laser annealing is demonstrated. The influence of unintentional annealing at elevated temperatures during fabrication of InGaN structures is revealed. A novel interpretation for negative correlation between photoluminescence intensity and band peak wavelength in high-indium-content InGaN multiple quantum wells is suggested. The enhancement of emission efficiency in InGaN quantum wells due to coupling of the optical dipole with localized surface plasmons in silver nanoparticles is investigated and the influence of potential fluctuations on the coupling with localized surface plasmons is revealed.
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Chua, Soo-Jin, Eugene A. Fitzgerald, and T. L. Song. "Graded InGaN Buffers for Strain Relaxation in GaN/InGaN Epilayers Grown on sapphire." 2003. http://hdl.handle.net/1721.1/3723.
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Graded InGaN buffers were employed to relax the strain arising from the lattice and thermal mismatch in GaN/InGaN epilayers grown on sapphire. An enhanced strain relaxation was observed in GaN grown on a stack of five InGaN layers, each 200 nm thick with the In content increased in each layer, and with an intermediate thin GaN layer, 10 nm thick inserted between the InGaN layers, as compared to the conventional two-step growth of GaN epilayer on sapphire. The function of the intermediate layer is to progressively relax the strain and to annihilate the dislocations that build up in the InGaN layer. If the InGaN layers were graded too rapidly, more dislocations will be generated. This increases the probability of the dislocations getting entangled and thereby impeding the motion of the dislocations to relax the strain in the InGaN layer. The optimum growth conditions of the intermediate layer play a major role in promoting the suppression and filling of the V-pits in the GaN cap layer, and were empirically found to be a thin 10 nm GaN grown at 750 0°C and annealed at 1000 0°C.Singapore-MIT Alliance (SMA)
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Song, T. L., Soo-Jin Chua, and Eugene A. Fitzgerald. "Graded InGaN Buffers for Strain Relaxation in GaN/InGaN Epliayers Grown on Sapphire." 2002. http://hdl.handle.net/1721.1/3975.
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Graded InGaN buffers are employed to relax the strain arising from the lattice and thermal mismatches between GaN/InGaN epilayers grown on sapphire. The formation of V-pits in linearly graded InGaN/GaN bulk epilayers is illustrated. The V-pits were sampled using Atomic Force Microscopy and Scanning Electron Microscopy to examine their variation from the theoretical geometry shape. We discovered that the size of the V-pit opening in linearly graded InGaN, with and without GaN cap layer, has a Gaussian distribution. As such, we deduce that the V-pits are produced at different rates, as the growth of the InGaN layer progresses. In Stage I, the V-pits form at a slow rate at the beginning and then accelerate in Stage II when a critical thickness is reached before decelerating in Stage III after arriving at a mean size. It is possible to fill the V-pits by growing a GaN cap layer. It turns out that the filling of the V-pits is more effective at lower growth temperature of the GaN cap layer and the size of the V-pits opening, which is continued in to GaN cap layer, is not dependent on the GaN cap layer thickness. Furthermore, graded InGaN/GaN layers display better strain relaxation as compared to conventionally grown bulk GaN. By employing a specially design configuration, the V-pits can be eliminated from the InGaN epilayer.Singapore-MIT Alliance (SMA)
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Hou, Po-Yi, and 侯博譯. "Analysis of the InGaN ∕ GaN LED With an InGaN ∕ GaN pre-buffer layer." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/39035406888124189176.
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碩士長庚大學
電子工程學研究所
96
Abstract The near-green light emitting diode (LED) samples used in this research were grown by atmospheric pressure metal-organic chemical vapor phase epitaxy (AP-MOVPE) system. Single/multiple InGaN pre-buffer layers were added into the basic structure of LEDs right beneath multiple quantum wells (MQWs). The three samples emit at 501.17 nm, 500.97 nm, and 494.36 nm, respectively. Many electrical property experiments, including I-V, L-I, EL spectra measurement, were applied with these samples to see how pre-buffer layer affect the performance of the devices. With our results, we found that samples with InGaN pre-buffer layer performed a lower forward voltage (0.6V lowered on the sample with multiple pre-buffer layers), higher output efficiency (25.8% higher under 20 mA) and stable wavelength shift while operating under different current.It is considered that applying InGaN pre-buffer layer into LEDs could be a good solution of improving epitaxy quality and device performance.
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Li, Shunfeng [Verfasser]. "Growth and characterization of cubic InGaN and InGaN/GaN quantum wells / von Shunfeng Li." 2005. http://d-nb.info/977177483/34.
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Lin, Hung Chin, and 林鴻欽. "Study of thermal effect on the optical properties of InGaN epilayer and InGaN LED." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/23713544826438831867.
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碩士國立交通大學
理學院光電半導體及奈米科技產業專班
97
In this thesis, thermal effect on the optical properties of InGaN epilayer and InGaN LED was investigated. In the section of thermal effect on the optical property of InGaN epilayer, the value of full-width at half-maximum (FWHM) of X-ray diffraction and photoluminescence (PL) spectrum were reduced after thermal annealing process. This is because of the crystal quality was improved by thermal annealing treatment. The red and blue shift of PL spectrum was observed in the different thermal annealing temperature. This is due to the In contain was changed in the InGaN epilayer after different thermal annealing temperature. In the section of thermal effect on the optical property of InGaN LED, the blue and red shift of PL spectrum was observed in the different thermal annealing temperature is due to the change of the potential energy of the quantum wells in LED structures. Beside, the intensity of the PL spectrum was increase with increasing the annealing temperature. The highest intensity was observed in the 700℃ annealed sample. Therefore, the optical properties of InGaN epilayer and InGaN LED can be improved by suitable annealing temperature.
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Lai, Yen-Lin, and 賴彥霖. "Microstructure and optical properties of InGaN/GaN multiple quantum wells comprised of InGaN dots." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/68553573907146093098.
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博士國立成功大學
材料科學及工程學系碩博士班
95
This dissertation explores the microstructure and optical properties of InGaN/GaN multiple quantum wells (MQWs) comprised of InGaN quasi-dots, which were grown by metalorganic chemical vapor deposition (MOCVD). Microstructure of the samples was characterized by high resolution transmission electron microscopy (HRTEM). The crystallinity and interface quality of the samples were determined by ω-2θ and ω-scan analysis with high resolution x-ray diffraction (HRXRD). The optical properties of the samples were investigated by combining low-temperature photoluminescence (PL), micro-PL, PL excitation (PLE) and time-resolved PL measurements. The main focus of this dissertation can be divided into five parts. First, we demonstrated that the emission wavelength of InGaN/GaN MQWs can be tuned from the blue to yellow in the visible spectral region by using InGaN dots. The common degradation phenomenon on crystallinity often observed in InGaN/GaN system with higher indium concentration was found being avoided by this kind of growth. In addition, we also found that the propagation of threading dislocations would be efficiently stopped by the quasi-dots, which behave as real quantum dots. Then, the indium content within the InGaN quasi-dots was estimated experimentally and theoretically. Comprehensive calculations including polarization, piezoelectric field and size effect help derive an indium composition of 59 % and 31 % for the In-rich clusters of 2 nm and 3 nm. We further demonstrated that the dominant emitting mechanism for green InGaN/GaN MQWs is polarization field, however, for blue InGaN/GaN, both size effect and polarization effect are equally important. In the third part, the effect of barrier growth temperature on blue InGaN/GaN MQWs was studied. It was found that the InGaN active layers composed of InGaN quasi-dots of 2±0.2 nm in diameter, changing from homogeneous nature, could be obtained by elevating the barrier growth temperature from 700 to 800 ºC. The strong piezoelectric field, “S-shape-like” carrier transition and high internal quantum efficiency of 71.3% were observed in the sample with a higher barrier growth temperature, closely related to the dots formation. Furthermore, the forward voltage and the light output power at 20 mA of light emitting diodes from the sample with dots were 0.3 V lower and 11% higher than that from the homogeneous multiple quantum wells. In the fourth part, the carrier transfer between InGaN dots and InGaN matrix was investigated in the green InGaN/GaN MQWs. Except for the strong indium aggregation, slight composition fluctuations were also observed in the InGaN matrix, which were speculated from an “S-shaped” transition and a Stokes shift of 341meV. In addition, a shorter lifetime and ‘two-component’ PL decay were also found for the InGaN matrix. Thus, the carrier transport process within quantum wells is suggested to drift from the low-In-content matrix to the high-In-content dots, resulting in the enhanced luminescence efficiency of the green light emission. The influence of material polarity on the emission properties of InGaN/GaN MQWs was discussed in the final part. A clear phase separation was observed both in Ga- and N-polarity samples, corresponding to two InGaN-related emissions ( InGaN dots and an InGaN matrix) seen in photoluminescence (PL) spectra. We demonstrated that the dot-related emission in the Ga-polarity MQWs shows stronger carrier localization, little influence by defects and higher temperature insensitivity as compared to N-polarity MQWs. In addition, the efficient carrier transport from the low-indium InGaN matrix to high-indium In-rich dots was observed in the Ga-polarity structure, but not in the N-polarity one.
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Chen, Peng-Ren, and 陳鵬壬. "AlGaN/GaN/InGaN Current Spreading Layer Used in High Power InGaN Light Emitting Diodes." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/63375579773752424098.
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碩士國立中央大學
電機工程研究所
98
In the application of white-light LED illumination, a bigger illuminating area is needed to increase output power and effectively raise conversion efficiency, further to achieve a high-power solid state lighting that can meet the requirements of energy saving, environment protection and low cost. However, the fact that the resistivity of N-type GaN semiconductor is greater than that of P-type transparent conducting layer can lead to current congestion around N-type electrode and result in local heat accumulation, which will drastically reduce quantum efficiency. In this study, a current spreading layer of dual- herterojunction (AlGaN/GaN/InGaN) was presented to improve the situation of current congestion when a LED of increased size is used. Additionally, a deeper exploration was conducted on structure simulation and photoelectric properties. In terms of the exploration of the photoelectric properties of LED with current spreading layer, comparison was made between luminous intensities of traditional GaN LED and LEDs with current spreading layer of heterojunctions of AlGaN/GaN and AlGaN/GaN/InGaN structures. The results showed that the luminous intensities of LED with current spreading layer of AlGaN/GaN and AlGaN/GaN/InGaN structures could be improved to 93.7 mW、105.6 mW、115.2 mW when 350mA is applied. On the other hand, due to piezoelectric polarization''s possible influence on the quantum confined stark effect of multi-quantum well, multi-quantum well with hetero-structure was measured using reciprocal lattice vector space to observe its stress change. Moreover, a qualitative polarization analysis was conducted on the wavelength of the excited light emitted from multi-quantum well to prove the effect of quantum well polarization won''t be affected by the output power of light. The measurements suggested that the light image uniformity variations were reduced to 31.5 %、24.3 %、21.4 % (Ref @ 500 mA) respectively and the temperatures measured when high current was applied were respectively lowered to 132.8 oC、120.1 oC、113.4 oC (Ref @ 350 mA), which proved that LED with current spreading layer presented in this study can improve the element''s heat stability for commercial use.
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Chin-Lan, Liao, and 廖浚男. "Microspectroscopy of InGaN/GaN Overlayers." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/61379299539637926645.
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碩士國立中山大學
物理學系
87
In this work, we study the properties of InGaN thin films using photoluminescence (PL) spectroscopy and imaging. A temperature variation series and a flux variation series of InGaN thin films were observed. It is well known that the energy gap is related to the concentration of indium, which is reflected in the PL spectra. By obtaining PL images at various wavelengths, the films' uniformity can also be characterized. In addition, micro-spectroscopy can be performed for micron size region. An important characteristics of these films is that spectra from the bright and dark spots do not show structural difference. In general we have found that films grown at higher temperature and indium flux exhibits better quality.
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Huang, Bo-Song, and 黃柏淞. "Ultrathin InGaN Light-Emitting Membranes." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/59049063619658877916.
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碩士國立中興大學
材料科學與工程學系所
104
In this study, GaN-based light-emitting diodes (LEDs) were lifted-off as a light-emitting diodes membranes by electrochemical wet etching technique. The heavy Si-doped GaN:Si sacrificial layer was inserted into the InGaN LED structure that the lateral wet etching rate had been enhanced. The ITO/Ti/Au layers deposited on p-GaN:Mg layer acted the protection layer and provided the mechanical strain during the lift-off processes. In the Raman spectra, the Raman peak of the NM-LED was observed at 566.3 cm-1 that had a 5.2 cm-1 shifted compared with the non-treated ST-LED (571.5cm-1). In the photoluminescence spectra, the peak wavelength of the NM-LED had a 4.0nm blueshifted compared to the ST-LED. The electroluminescence spectra were measured at 529.9nm for ST-LED and 524.4nm for the NM-LED, respectively. The divergent angle of the NM-LED was 97° that was narrowed compared with the ST-LED (113°).
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Oppo, Carla Ivana. "Development of InGaN/GaN nanostructures." Doctoral thesis, 2017. http://hdl.handle.net/11858/00-1735-0000-002B-7D31-B.
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Liu, Wen-Hung, and 劉文宏. "Characterization of InGaN-based Photodetectors." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/gmg3b5.
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碩士國立虎尾科技大學
光電與材料科技研究所
96
In recent years, the optoelectronic devices breaks through in development and application field. Especially, some most important novel technology was developed in III-V semiconductor materials. We can modulate the energy band gap by concentration of indium doping in Nitride based semiconductor materials. Thus, it was used to change the absorption and emitting wavelength of semiconductor materials in led and solar cell devices. In this study, we based on design the contact pattern of OE (optoelectronic, OE) devices. The characteristic was varied by thickness of metal bar and numbers on the surface of InGaN OE devices. The InGaN p-i-n UV-A+B photodetector successfully were grow and fabricated by Metal-Organic Chemical Vapor Deposition (MOCVD). The differently between dark and photo current, have 3 orders. The wavelength of light source is at 380nm. The photo response and rejection ratio of PD have 0.107A/W and 1620. We change the p-type material, the difference between dark and photo current that have 5 orders lager than the other samples.
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Chen, He-Yi, and 陳和毅. "Enhanced Light Output Power by Embedded InGaN Strain Reduce Layer in InGaN Multiple-Quantum-Well LED." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/61553210912659361157.
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碩士長庚大學
光電工程研究所
94
In this research, we investigated the characterizations of the InxGa1-xN strain reduce layer embedded in the InGaN multi-quantum-well LED. The high-resolution reciprocal space mapping (RSM) showed that the compressive strain relaxation occurred more considerably and the average Indium fraction was increased in MQW structure. The temperature-dependent photoluminescence (TDPL) spectrum showed two emission regions, and the dominant peak had temperature-induced S-shaped PL shift corresponding to Indium rich regions. The reverse current-voltage (I-V) characteristics of the LEDs with heavy strain relaxation of MQW showed leakage current higher than conventional LEDs. Even if the LEDs with InxGa1-xN strain reduce layer had poor quality, the indium rich regions could protect the carriers in the MQW structure from the defect capturing and quantum confined stark effect, as that and then we would get the superior internal quantum efficiency from light output-current characteristics. We could understand that Indium rich regions inside the MQW structure could generate by embedded InxGa1-xN strain reduce layer, which was related to an improvement of the LED light output power.
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Liu, Tzu-Chi, and 劉子綺. "Optical Studies on InGaN/GaN Nanostructures." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/78939477096933838064.
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碩士國立臺灣大學
光電工程學研究所
96
In this research, we first demonstrate superior optical quality of a-plane GaN grown on r-plane sapphire substrate based on the flow-rate modulation epitaxy (FME) technique, in which the Ga atom supply is alternatively switched on and off with continuous nitrogen supply. Based on the results of photoluminescence measurements, one can observe the better optical property of the FME-grown a-plane GaN thin film. Besides, it was shown that strain was more relaxed in the FME sample. Then, we demonstrate the enhanced emission efficiency and reduced spectral shifts of a green InGaN/GaN quantum-well (QW) light-emitting diode epitaxial structure by using the prestrained growth technique. By adding a ~7 %-indium InGaN/GaN QW to the structure before the growth of designated emitting high-indium QWs, the growth temperature of the emitting QWs can be raised by 30 oC while keeping about the same emission wavelength around 544 nm in photoluminescence (PL). The internal quantum efficiency and room-temperature PL intensity are increased by ~167 and ~140 %, respectively.
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Guan-RuLiu and 劉官儒. "Piezo-phototronic Effects of InGaN Nanorods." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/34087897529780672526.
Full textAbstract:
碩士國立成功大學
物理學系
104
InGaN nanorods are grown on Si (111) substrates by using plasma-assisted molecular beam epitaxy (PA-MBE). The composition ratio of In/Ga in InGaN nanorods was manipulated by changing substrate temperature under the same indium, gallium, and nitrogen plasma flux. The photoluminescence spectra of InGaN nanorods are shifted to longer wavelengths due to the increasing of In composition while decreasing the substrate temperature. The piezoelectric performance and piezo-phototronic effects were demonstrated in the vertical integrated nanogenerators (VING) based on InGaN nanorods in varying indium composition. We show that higher output voltage of InGaN nanogenerators higher indium composition in InGaN nanorods. In addition, the output voltage of InGaN nanogenerators was also increased under the visible light illumination.