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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Conception et caractérisation de diodes en SiC pour la détermination des coefficients d'ionisation

Nguyen, Duy Minh 20 June 2011 (has links) (PDF)
Le carbure de silicium (SiC) possède plusieurs propriétés exceptionnelles comme une large bande interdite, un champ électrique critique et une vitesse de saturation des porteurs élevée pour remplacer le silicium (Si) dans des domaines de fonctionnement jusque-là inaccessibles avec le Si. Un nombre important de démonstrateurs des composants de puissance en SiC faisant état de performances remarquables ainsi que la disponibilité commerciale des composants en SiC confirment la maturité de la filière SiC et montrent les progrès technologiques réalisés au cours des dernières années. Cependant, il existe peu d'études sur les coefficients d'ionisation du SiC, lesquels sont pourtant indispensables pour prévoir précisément la tenue en tension des composants de puissance en SiC. Ce travail contribue donc à mieux déterminer ces coefficients. Pour cela, un bon nombre de diodes spécialement conçues pour la détermination des coefficients d'ionisation du SiC par la technique OBIC (Optical Beam Induced Current) ont été réalisées sur différents wafers de SiC-4H et de SiC-6H, deux polytypes courant du SiC. Cette technique repose sur un faisceau de laser ultraviolet qui génère des paires électrons-trous dans la zone de charge d'espace d'une diode sous test. La mesure du courant résultant permet d'accéder aux coefficients d'ionisation. A partir des mesures OBIC sur les diodes réalisées, nous avons pu déduire les coefficients pour ces deux polytypes du SiC. Plus particulièrement, les coefficients d'ionisation du SiC-4H sont déterminés dans une large gamme de champ électrique grâce aux mesures sur les différents dopages. Les paramètres des coefficients déterminés dans ce travail peuvent être utilisés en conception de dispositifs haute tension pour prédire plus précisément l'efficacité de leur protection périphérique.
22

Microanastomoses vasculaires assistées par laser diode 1950 nm en chirurgie plastique réparatrice : étude expérimentale et clinique / 1950 nm diode laser-assisted vascular microanastomoses in reconstructive plastic surgery : experimental and clinical study

Leclère, Franck 13 December 2011 (has links)
En chirurgie plastique, le succès des lambeaux libres et des replantations dépend largement de la qualité des microanastomoses vasculaires. Ce travail complète les bases scientifiques de la technique de microanastomoses assistées par laser diode 1950 nm par la mise au point d’une méthode standardisée et l’étude post-opératoire du débit sanguin sur des séries animales. Il pose les jalons des premières séries cliniques. Dans une première série animale (S1), 30 anastomoses terminoterminales carotidiennes et 30 anastomoses jugulaires sont effectuées par la technique laser diode 1950 nm chez des rats Wistar. Les paramètres lasers suivants sont utilisés: taille du spot 400 µm, temps 1s, puissance délivrée de 100 mW à 150 mW (carotides) et de 90 mW à 140 mW (veines jugulaires). Elles sont comparées à J0 puis après 1, 4 et 12 semaines postopératoires, à un groupe contrôle de 30 anastomoses artérielles et de 30 anastomoses veineuses dans les mêmes proportions réalisées à l’aide de la technique conventionnelle par fils. Deux autres séries animales S2 et S3 sont ensuite entreprises à l’aide des paramètres lasers mis en évidence dans l’étude S1. Une série S2 regroupant vingt microanastomoses terminoterminales carotidiennes de rats Wistar est réalisée par la technique laser (n=10, P=120mW, spot 400 μm, durée du spot 1s, 5 spots par paroi, fluence 95 J/cm²) et la technique conventionnelle par fils 10/0 (groupe contrôle, n=10). Pour les deux groupes, la carotide controlatérale non opérée sert de référence pour le calcul du débit sanguin par IRM de flux : Une séquence de positionnement, une séquence anatomique, une séquence angiographique et une séquence de flux sont réalisées un jour après l’opération puis après une, quatre et huit semaines. Une série S3 regroupant vingt microanastomoses terminoterminales jugulaires de rats Wistar est réalisée par la technique laser (n=10, P=110mW, spot 400 μm, durée du spot 1s, 4 spots par paroi, fluence 90 J/cm²) et la technique conventionnelle (groupe contrôle, n=10). De même la jugulaire controlatérale sert de référence dans les diverses séquences IRM. Au total, 40 actes microchirurgicaux comprenant 38 lambeaux libres et 2 replantations digitales sont réalisés à l’aide du laser diode 1950 nm. Les microanastomoses artérielles sont terminoterminales dans 36 cas et terminolatérales pour 4 autres. Les microanastomoses veineuses sont toutes terminoterminales. Les microanastomoses sont réalisées par un laser diode 1,95 µm après mise en place de 2-5 points de rapprochement. Les paramètres suivants sont utilisés : taille du spot 400µm, puissance 125mW, 4 à 8 spots sur chaque face, temps d’application (0,7-2s) suivant le diamètre des vaisseaux : la fluence varie de 70 à 200 J/cm². Les études du débit sanguin par les nouvelles techniques d’IRM de flux avec les paramètres maintenant standardisés mettent en évidence l’excellente perméabilité des anastomoses laser sur un modèle animal. Le taux de succès de cette première grande série clinique apparait excellent lorsque comparé à celui des grandes séries de la littérature. Les innovations technologiques devraient conduire à une utilisation plus large de cet outil au bloc opératoire. / In the field of plastic surgery, the most important factor for successful free flap transfer and replantations is a well executed vascular microanastomosis. The aim of these studies is to complement the scientific basis of the 1950 nm diode laser assisted microanastomosis (LAMA) by standardising the technique and studying the postoperative blood flow in animal series. This work introduces the first clinical series. In the first animal series (S1), 30 end-to-end microanastomoses of the carotidis and 30 end-to-end microanastomoses of the external jugular were performed with a 1950 nm diode LAMA technique in Wistar rats. The following laser parameters were used: spot size=400µm, spot duration=1s, Power varying between 100 to 150 mW for arterial microanastomoses and between 90 to 140 mW for venous microanastomoses. They were compared at D0 and at 1, 4 and 12 weeks with 30 conventional arterial microanastomoses and 30 conventional venous microanastomoses.Two other animal series (S2 and S3) were performed using the standardised parameters of the initial studies. In the S2 series, LAMA was performed on a group of 10 carotidis on Wistar rats. Two 10/0 stay sutures and a standard laser tissue welding technique (P=120mW, spot size=400 μm, t=1s, 5 spots for each wall, fluence=95 J/cm²) were used (LAMA group). They were compared with a group of 10 conventional arterial anastomosis (CSMA group). A MRI-positioning sequence (Magnetic Resonance Imaging), an anatomical sequence, an angiographic sequence and a flow sequence were performed 1 day after operation and then after 1, 4 and 8 weeks. Similarly, the series S3 included 20 microanastomoses of the external jugular performed with LAMA (n=10, P=110mW, spot size=400 μm, spot duration= 1s, 4 spots for each wall, fluence 90 J/cm²) or the conventional technique (n=10). For the two groups, contralateral non-operated external jugular were used as control.In total, 40 clinical procedures, including 38 free flaps and 2 finger replantations have been performed with the LAMA technique. End-to-end arterial microanastomoses were performed in 36 cases and end-to-side in 4 cases. All venous microanastomoses were performed end-to-end. LAMA was performed with a 1950 nm diode laser after placement of 2-5 stitches. The following laser parameters were used: spot size=400 μm, spot duration=0.7-2s, 4-8 spots for each wall, power=125 mW, fluence=70-200 J/cm². The animal series S1 demonstrates excellent bloodless patency at fluences ranging from 90 to 100 J/cm² (Power between 110-130mW) for arterial LAMA, and between 80 and 95 J/cm² (Power between 100-120mW) for venous LAMA. The flow-MRI further demonstrates that 1950 nm diode laser-assisted microanastomoses performed with our standardised parameters is a consistent, reliable and reproducible technique. The success rate of the clinical series appears promising. Technical innovation will most likely lead to greater ease of use of the laser handpiece in the operating room.
23

Laser de Nd:YLF para aplicações em LIDAR / LASER DE Nd:YLF PARA APLICAÇÕES EM LIDAR

Marco Antonio Ferrari 14 October 2008 (has links)
A utilização de lasers de estado sólido bombeados por diodos laser tem atraído interesse crescente devido a sua alta eficiência, seu tamanho compacto e com a possibilidade da operação com altas potências-pico. O objetivo deste trabalho foi estudar configurações de cavidades ressonantes laser, que possibilitem a obtenção de pulsos chaveados Q e futura dobra de freqüência, para aplicações em LIDAR (Light Detection and Ranging), utilizando como meio ativo cristais de Nd:YLF crescidos pelo método de Czochralski no Centro de Lasers e Aplicações IPEN USP, com bombeio lateral por diodo laser, com uma, duas, quatro e nove reflexões internas totais do feixe laser na superfície do cristal. Das seis cavidades construídas, três cavidades foram desenvolvidas para operarem com baixo ganho, grande armazenamento de energia e com grande aproveitamento de inversão de população, bombeadas com diodo laser em 806 nm e outras três cavidades foram desenvolvidas para operarem com alta absorção de bombeio e alto ganho, bombeadas com diodo laser emitindo em 797 nm. Das seis cavidades desenvolvidas, as que apresentaram melhor eficiência de conversão óptica, foram as cavidades operando com alto ganho e alta absorção (cavidade quatro a seis), com 29,5% e 20,7% de eficiência de conversão óptica, propiciando a obtenção de pulsos chaveados de 20 ns com potência-pico de 160kW. / The use of diode pumped, solid state lasers has caused increasing interest due its high efficiency, compactness and possibility of operation in high peak powers. The goal of this work was the study of configurations of laser resonators that allow to obtain Q-switched pulses and a future frequency doubling, for LIDAR (Light Detection and Ranging) applications. Using as active medium Nd:YLF crystals grown by the Czochralski method at the Centro de Lasers e Aplicações IPEN USP, side pumping by laser diodes, with one, two, four and nine total internal reflexions of the laser beam at the surface of the crystals was employed. From the six resonators built, three of them were designed to work with low gain, pumped by a laser diode emitting at 806 nm. Another three laser resonators were designed to work with high pump absorption and high gain, pumped by a laser diode emitting at 797 nm. From the six developed resonators, the ones which showed the best optical conversion efficiency, were the resonators designed to work with high gain and high absorption (resonator four to six), showing 29,5% and 20,7% optical conversion efficiency, and enabling obtaining Q-switched pulses of 20 ns, with 160 kW peak power.
24

Laser de Nd:YLF para aplicações em LIDAR / LASER DE Nd:YLF PARA APLICAÇÕES EM LIDAR

Ferrari, Marco Antonio 14 October 2008 (has links)
A utilização de lasers de estado sólido bombeados por diodos laser tem atraído interesse crescente devido a sua alta eficiência, seu tamanho compacto e com a possibilidade da operação com altas potências-pico. O objetivo deste trabalho foi estudar configurações de cavidades ressonantes laser, que possibilitem a obtenção de pulsos chaveados Q e futura dobra de freqüência, para aplicações em LIDAR (Light Detection and Ranging), utilizando como meio ativo cristais de Nd:YLF crescidos pelo método de Czochralski no Centro de Lasers e Aplicações IPEN USP, com bombeio lateral por diodo laser, com uma, duas, quatro e nove reflexões internas totais do feixe laser na superfície do cristal. Das seis cavidades construídas, três cavidades foram desenvolvidas para operarem com baixo ganho, grande armazenamento de energia e com grande aproveitamento de inversão de população, bombeadas com diodo laser em 806 nm e outras três cavidades foram desenvolvidas para operarem com alta absorção de bombeio e alto ganho, bombeadas com diodo laser emitindo em 797 nm. Das seis cavidades desenvolvidas, as que apresentaram melhor eficiência de conversão óptica, foram as cavidades operando com alto ganho e alta absorção (cavidade quatro a seis), com 29,5% e 20,7% de eficiência de conversão óptica, propiciando a obtenção de pulsos chaveados de 20 ns com potência-pico de 160kW. / The use of diode pumped, solid state lasers has caused increasing interest due its high efficiency, compactness and possibility of operation in high peak powers. The goal of this work was the study of configurations of laser resonators that allow to obtain Q-switched pulses and a future frequency doubling, for LIDAR (Light Detection and Ranging) applications. Using as active medium Nd:YLF crystals grown by the Czochralski method at the Centro de Lasers e Aplicações IPEN USP, side pumping by laser diodes, with one, two, four and nine total internal reflexions of the laser beam at the surface of the crystals was employed. From the six resonators built, three of them were designed to work with low gain, pumped by a laser diode emitting at 806 nm. Another three laser resonators were designed to work with high pump absorption and high gain, pumped by a laser diode emitting at 797 nm. From the six developed resonators, the ones which showed the best optical conversion efficiency, were the resonators designed to work with high gain and high absorption (resonator four to six), showing 29,5% and 20,7% optical conversion efficiency, and enabling obtaining Q-switched pulses of 20 ns, with 160 kW peak power.
25

Homojunction and Heterojunction LightEmitting Diodes of Poly-(N-vinylcarbazole)and Dye Molecules

Sheu, Tian-Syh 13 July 2001 (has links)
ABSTRACT Organic light emitting diode (OLED) has significant scientific implication and technological potential. Using organic materials for tailored emitting color, threshold voltage reduction, and emission efficiency gain are the key points for the commercialization of OLED. An UV-Vis spectrophotometer was applied to obtain the absorption spectra of PVK, C6, and PRL, as well as their respective band gap (Eg) values of 3.49 eV, 2.32 eV, and 2.55 eV. The turn-on oxidation potential of cyclic voltammograms was reduced for HOMO energy at 5.64 eV, 5.21 eV, and 5.16 eV, respectively. The Eg subtracted from HOMO energy yielded the respective LUMO values of 2.15 eV, 2.89 eV and 2.61 eV. Excitation at 457 nm or 325 nm was applied to the freestanding films of PVK, PVK doped with C6 (10/1), and PVK doped with PRL (10/1). From the UV-Vis absorption spectra and Egs, we knew that 457 nm excitation did not generate photoluminescence (PL) of PVK. The PL spectra of the doped freestanding films were mostly attributed to the dye molecules of C6 or PRL. The PL spectra of doped freestanding films were insensitive to the excitation sources at 325 nm and 457 nm. There was a blue shift at the PL emission peak indicative of energy transfer from PVK to C6 or PRL for the doped films. Using spin-coating or vacuum deposition to fabricate PVK, C6, and PRL films onto an ITO substrate followed by evaporating Al (Ag) as the electron injector to form OLED devices. Because of the energy transfer between PVK and C6 or PRL, ITO/PVK:C6/Al homojunction OLED showed a smaller threshold voltage than that of ITO/C6/Al, from 9 V to 3.5 V. Likewise, ITO/PVK:PRL/Al homojunction OLED had a smaller threshold voltage than that of ITO/PRL/Al, from 8 V to 4.5 V. PVK was also used as the hole blocking layer to construct heterojunction OLED to balance electron-hole numbers in the emitting layer. The threshold voltage of ITO/C6/Al reduced from 9 V to 7 V with a heterojunction of ITO/PVK/C6/Al. A device of ITO/PRL/Al having a threshold voltage of 8V reduced to 6V with an ITO/PVK/PRL/Al heterojunction OLED. Coating a protective layer (Ag) on the metallic electron injector, or packaging the device in N2 could both decrease the decay and increase the life time of OLED.
26

Stress Dependent Behaviour of InGaAsP Semiconductor Diode Lasers

Adams, Charles 08 1900 (has links)
The effects of tension and compression applied to unbonded InGaAsP semiconductor diode lasers have been studied. A theoretical calculation of the stress distribution within the laser and an analysis of the effect of strain on optical gain in semiconductors is presented. The observed dependence of threshold, wavelength, and polarization of the laser output on the applied stress is explained in terms of the strain dependence of the valence-band wavefunctions. The polarization behaviour is found to be related to thermal stress and the structure of the device. A technique has been developed to measure the thermal stress induced by current heating at the 105 dynes/cm2 level. The effect of stress on the below threshold behaviour of the lasers was investigated. The results are consistent with the strain dependence of the TE and TM mode gains. / Thesis / Master of Engineering (ME)
27

RF-Sputtering of ZnO thin films on Si(111) substrates : the effects of Al2O3 buffer layers and the pin diode formation

Wang, Jun-Hau 25 August 2011 (has links)
RF magnetron sputtering has been employed to deposit n-type epitaxial zinc oxide thin films on p-type silicon substrates to form p-n diode structures. Commonly found on silicon, native SiOx layers, typically of a few nanometer thick, would hinder the epitaxial growth of ZnO. In this thesis work, a crystalline metal oxide layer was introduced as a buffer layer by redox reaction between a metal layer and the native SiO2. Aluminum was first sputtered for 20 seconds (4 nm), 40 seconds (8 nm), 60 seconds (12 nm) to produce three sets of samples. Each set was then annealed in situ at 450¢J for 20 minutes, 40 minutes, 60 minutes, respectively, to generate 9 different fabrication conditions meant to ignite a redox reaction between aluminum and the silicon oxide. All samples were treated for comparison by rapid thermal annealing to 900¢J, intended to improve the crystalline quality of the buffer layer and thus the epitaxial zinc oxide. Means to characterize the samples included (1) cross-sectional TEM (Transmission Electron Microscopy) observations of the interfaces and defects in various regions of the formed material or device structures; (2) x-ray crystallography via £s-2£c and rocking scans in regards to the perfection of the crystal structures and the relative film-substrate orientations; (3) photoluminescence spectroscopy, which showed oxygen deficiency in the ZnO epitaxial thin films as judged by the peaks of near-edge luminescence and mid-gap impurity states. The resulted material structure is a pin diode with a transparent n-ZnO layer sandwiching in the middle an aluminum oxide insulating layer with the p-Si substrate. The electrically insulating aluminum oxide layer serves to increase the minority carrier accumulation effect, extending carriers¡¦ effective life times and hence enhancing the light emission efficiency. Measuring the current-voltage characteristics of the pin device structures provides insights into the interface charges, while high-frequency capacitance-voltage curves helps give a glimpse of the interfaces between ZnO and Al2O3 or AlOx, as well as those between Al2O3 or AlOx and silicon, all concerning the electronic accumulations at each interface. Keywords: sputtering, ZnO, Al2O3 , pin diode.
28

Effects of fabrication processes on the electrical properties of n-ZnO/AlxSi(1-x)Oy/p-Si pin diodes

Lin, Jiun-jie 12 September 2012 (has links)
In this thesis, n-type ZnO thin films are grown on buffered p-type Si substrates by RF sputtering. The buffer is a pure nanometer-thick Al layer deposited onto a Si substrate that has a native SiOx over-layer. The Al- layer is meant to react with the native oxide and reduce it back to the pure Si formation when the Al-layer is itself oxidized into AlOx. The pin diodes with ZnO grown on AlOx are expected to outperform those with ZnO on SiOx on the aspects of electrical quality and crystallographic orientations. The transmission electron microscopy was employed to study the epitaxial relationship between the ZnO layers and the Si substrates, the crystal structure, and defects at the ZnO-Al or Al-SiOx interfaces. X-ray diffraction studies through £s-2£c, rocking curve, GIXRD and pole-figure scans were also conducted to see the differences between as-deposited and post-annealing treated samples concerning with the ZnO crystallographic orientations and general qualities. Through comparisons of the leakage current and the tunneling behaviors , the electrical measurements can be used to analyze the pin devices.
29

Current Transport Mechanisms in Organic Light-Emitting Diode

Ou, Yi-fang 01 July 2005 (has links)
Organic light-emitting diode has several advantages using in the flat penal display, but it is still needed to improve the disadvantages. The charge-carriers of the organic layers are one of the dominant factors to influence the performance of OLED. Hence, it is worth to study and understand the charge transporting behaviors by the theoretical simulation in the organic layers of OLED, and that is helpful for the OLED in future. In this study, three kinds of models are used to simulate the characteristics of several different organic light-emitting devices, and it also try to compare the relationship between the current density and voltage. Three kinds of models are described as (1) The field-dependent carrier mobility model (FDM model), (2) An exponential distribution of traps model (EDT model), and (3) The field dependent trap occupancy model (FDTO model). For the simulation of three models, the characteristics of several hole-only devices and electron-only devices were analyzed to investigate and discuss the organic layer of the devices with different materials. In addition, by varying the parameters such as the thickness and temperature, a comparison was made between the results simulated from models with the values obtained from experimental works. Finally, based on above results, the characteristics of OLED could be improved for future applications.
30

A Simple Package Technique of Light Emitting Diode for Enhancing Illuminant Quality

Lin, Yu-Chung 20 June 2008 (has links)
The purpose of this thesis is to fabricate an LED module with low half intensity angle(HIA) ,and to use this module to form a line source with optical performance comparable to that of a CCFL .In addition ,heat dissipation of the LED module on different sub-mounts is also investigated . The LED modules were formed by first etching a through si via on silicon substrate using wet etching technology for light confining .Then a thin layer of metal was deposited on to the via to reflect the lights emitted from the LED .The LED die was attached to the Si sub-mount with electrodes ,and the connections between the LED and the Si sub-mount were completed by wire bonding .Finally ,the LED modules were obtained by positioning the Si substrates onto the Si sub-mounts using UV epoxy . The optical performance of the LED module was simulated by Lighttools .For the si substrate with a thickness of 400 £gm ,a simulated HIA of 36 o was obtained .Using six-LED package ,a 3-cm line source with 84.8% output uniformity was simulated .On the other hand ,the measured HIA of a LED module ,and the uniformity of 3-cm line source are 38 o and 84.8% ,respectively. The thermal resistance of the si sub-mounts were also investigated .The different structures of the sub-mount were proposed ,namely ,LED to Copper case ,LED to Si sub-mount to Copper case ,and LED to Si sub-mount with Copper filled via to Copper case .The estimated thermal resistance of the sub-mounts are 13 W/mk¡B19.4 W/mk and 34.7 W/mk .We believe that the large thermal resistance of the Si sub-mount with Copper filled via is primarily caused by 800 £gm thick substrate .

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