Ce travail de thèse, réalisé au sein du CEA-LETI, consiste en la décorrélation des différents mécanismes ayant lieu dans une LED à base de GaN par voie de simulation numérique et de caractérisation expérimentale. Dans les chapitres 1 et 2, les théories des différents mécanismes présents dans une diode/LED sont décrites. Dans le chapitre 3, la simulation numérique d’une structure LED VTF ("vertical thin film" en langue anglaise) détermine les mécanismes prédominants dans les différentes gammes de tension. Une étude paramétrique s’ensuit afin d’évaluer les interactions entre les mécanismes.Dans le chapitre 4, les simulations sont effectuées en ajoutant un modèle de dépendance des mobilités des porteurs au champ électrique. En présence de ce modèle, les caractéristiques électro-optiques simulées tendent vers les caractéristiques réelles à haute tension.Les résultats des mesures de vitesse des porteurs dans le GaN-p sont également reportés dans le chapitre 4. En utilisant un motif d’échantillon spécifique et la méthode de mesure quatre points, les résultats suggèrent une tendance à saturer de la vitesse des porteurs, ou une tendance à décroître de la mobilité, à fort champ électrique. Ces résultats renforcent l’hypothèse de simulation utilisée dans le chapitre 4.Les simulations présentées dans les chapitres 3 et 4 permettent de proposer un schéma équivalent d’une LED en décorrélant les différents mécanismes et en ne gardant que les mécanismes dominants. Ce schéma équivalent permettrait, par exemple, à identifier les différents régimes dans une caractéristique électrique d’une LED réelle afin de procéder des améliorations du fonctionnement de la LED.Le chapitre 5 présente une étude par électroluminescence pulsée, une méthode de caractérisation fréquentielle, sur des LED commerciales. L’étude des temps de montée et de descente des signaux électro-optiques, ainsi que l’étude de durée de vie différentielle des porteurs de charge dans une LED, fourniraient des informations supplémentaires concernant l’injection des porteurs dans la LED. / This PhD. works, which was carried out inside CEA-LETI, aims to dissociate the various mechanisms occurring inside a GaN-based LED employing numerical simulation and experimental characterization. In the chapters 1 and 2, various mechanisms occurring inside a diode/LED are theoretically described. In chapter 3, through numerical simulation, the dominant mechanisms as well as their locations in a VTF ("vertical thin film") LED structure are determined for different voltage ranges. A parametric study follows to assess the interactions between the mechanisms.In chapter 4, the simulations are carried out with an additional field-dependent model for charge carrier mobility. With this model enabled, the simulated LED-electrical-and-optical characteristics approximate the real LED characteristics.Carrier-velocity characterization on p-type GaN, using a specific sample structure and the resistivity method, is also shown in chapter 4. It can be inferred from the results that under strong electric-fields, the carrier velocity might saturate, or the carrier mobility might decrease. These results strengthen the hypothesis used for the simulations in this chapter 4.The simulations introduced in the chapters 3 and 4 allow the proposition of an equivalent circuit for a GaN-based LED by dissociating the different mechanisms and retaining the dominant ones. This equivalent circuit could help, for instance, identify the different regimes in a real-LED electrical characteristics in order to improve the LED’s performance.Chapter 5 introduces pulsed electroluminescence, a frequential characterization method, on commercial LEDs. The studies of rise-time and fall-time of electro-optical signals, and the study of the differential lifetime of charge carriers in an LED would provide supplementary information concerning the carrier injection into the LED.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / Este trabalho apresenta o estudo, o projeto e a implementaÃÃo de um driver trifÃsico para diodos emissores de luz (LEDs) baseado num conversor com capacitor chaveado (SC â Switched Capacitor), tambÃm conhecido como charge-pump. Uma luminÃria LED com a tecnologia Chip-on-Board (COB), que proporciona uma elevada densidade de potÃncia, à utilizada como carga. Assim como os LEDs, os drivers destes dispositivos devem apresentar uma longa vida Ãtil e um elevado rendimento. A vida Ãtil dos drivers para LEDs à geralmente limitada pelo uso de capacitores eletrolÃticos convencionais. Estes dispositivos apresentam uma vida Ãtil incompatÃvel com a dos LEDs e, por isso, nÃo devem ser utilizados nos seus drivers. AlÃm disso, os drivers para LEDs devem proporcionar uma baixa ondulaÃÃo de corrente nos LEDs, garantindo um baixo flicker percentual e evitando danos à saÃde humana. Diante destes problemas, o conversor trifÃsico SC proposto nÃo utiliza capacitores eletrolÃticos, o que eleva a expectativa de vida Ãtil do driver. O conversor emite um baixo flicker percentual e à capaz de estabilizar a corrente de saÃda sem a necessidade de um controle de malha fechada, o que pode reduzir os custos de projeto. A topologia permite a dimerizaÃÃo dos LEDs atravÃs da variaÃÃo da frequÃncia de comutaÃÃo. Resultados experimentais de um protÃtipo de 216 W sÃo analisados e discutidos para validaÃÃo da proposta. Em condiÃÃes nominais, o conversor apresentou um rendimento global de 91,5%, um fator de potÃncia acima de 0,99 e uma distorÃÃo harmÃnica menor que 5% nas trÃs fases, obedecendo as Classes A e C da norma IEC 61000-3-2:2014. AlÃm disso, foi obtida uma ondulaÃÃo de corrente de alta frequÃncia igual a 16,97% e um flicker percentual de 4,97%, estando de acordo com as recomendaÃÃes da IEEE. A dimerizaÃÃo dos LEDs permitiu a reduÃÃo da potÃncia de saÃda em atà 50%, com rendimento prÃximo a 91%, fator de potÃncia acima de 0,97, distorÃÃo harmÃnica total inferior a 6% para as trÃs fases e flicker percentual menor que 7% para toda a faixa de potÃncia. / This paper presents the study, design and implementation of a three-phase light-emitting diode (LED) driver based on a switched capacitor (SC) converter, also known as charge-pump. A LED lamp with Chip-On-Board (COB) technology, which provides a high power density, is used as load. As the LEDs, drivers of these devices must have a high efficiency and a long useful lifetime, which is usually limited by the use of conventional electrolytic capacitors. These devices have an incompatible lifetime with LEDs and, therefore, they should not be used in their drivers. In addition, the LED drivers should provide a low ripple current in LEDs, which can provide the emission of a low percent flicker. Studies demonstrate that excessive percent flicker may cause damage to human health. Given these problems, the proposed switched capacitor LED driver does not use electrolytic capacitors, which increases the expectative of useful lifetime of the driver. It emits a low percent flicker, which reduces the risks to human health. It can stabilize the output current without the need of a closed-loop control, which may reduce design costs. It allows the LEDs dimming by varying the switching frequency. An experimental prototype rated at 216 W has been developed in order to evaluate the performance of the proposed approach, while results are properly presented and discussed. In nominal conditions, the drive presented an overall efficiency of 91.5%, a power factor greater than 0.99 and a current total harmonic distortion lower than 5% in three phases. The harmonic currents are in accordance with the limits imposed by IEC Standard 61000-3-2:2014 to class A and C equipment. Furthermore, a high frequency current ripple equal to 16.97% and a percent flicker of 4.97% was obtained, which is in accordance with IEEE recommendations. The LEDs dimming allowed the reduction of the output power up to 50%, while the efficiency remained close to 91% and the power factor remained above 0.97. In addition, the total harmonic distortion was below 6% and the percent flicker was lower than 7% for the entire dimming range.