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Jahresbericht / Institut für Halbleiter- und Mikrosystemtechnik der Technischen Universität Dresden18 May 2012 (has links)
Jahresbericht des Instituts für Halbleiter- und Mikrosystemtechnik der Technischen Universität Dresden
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Identifikation von Transport- und Rekombinationskanälen zur Optimierung (AlGaIn)N basierter licht-emittierender HalbleiterdiodenBinder, Michael 19 January 2023 (has links)
Nitridbasierte LEDs bilden nicht nur die Basis für eine effiziente weiße Lichterzeugung, sondern halten auch durch eine Vielzahl weiterer Applikationen, wie zum Beispiel als Emitter bei der Pulsvermessung bei smart wearables oder auch in Displays, in unser Leben Einzug.
Die Untersuchung der physikalischen Effekte, welche die elektrooptischen Eigenschaften (AlGaIN)N-basierter LEDs, insbesondere die Effizienz, bestimmen, sowie deren Abhängigkeit von der Emissionswellenlänge und vom Betriebsstrom der LED, ist Gegenstand dieser Arbeit.
Es wird ein physikalisches Model zur Beschreibung der Strom-Spannungscharakteristik moderner blaue LEDs aufgestellt. Dieses bringt die LED-Spannung mit der internen Rekombinationsdynamik in Verbindung und ermöglicht somit die Vorhersage der Effizienz aus der Bestimmung rein elektrischer Kenngrößen.
Die physikalische Ursache für den Effizienzabfall blauer sowie grüner LEDs im Bereich hoher Ströme war lange Zeit Gegenstand einer intensiv geführten Debatte in der Literatur. Mit dem in dieser Arbeit entwickelten Konzept zur Visualisierung von Auger-Prozessen kann bewiesen werden, dass dieses auch als Droop bezeichnete Problem auf Auger-Rekombination zurückzuführen ist.
Aufbauend auf diesem Befund wird ein neuartiges Konzept zur Abmilderung des Droops aufgezeigt: Durch gezielte Einbringung einer dreidimensionalen Struktur lässt sich der Ladungsträgertransport verbessern und somit der Verlustkanal bei hohen Stromdichten verringern.:1 Einleitung
2 Grundlagen
3 Exemplarische Herleitung grundlegender Kenngrößen einer typischen LED
4 Effizienzuntersuchungen an SQWs unterschiedlicher Wellenlänge
5 Untersuchung der Kleinstromeffizienz
6 Der Droop – Untersuchung des Hochstromverlustkanals
7 Verminderung des Droops - V-förmige Defekte zur Löcherinjektion
8 Zusammenfassung / III-Nitride based LEDs not only constitute the basis for an efficient generation of white light, but they also play an increasingly important role in our lives by many new applications such as vital sign monitoring with smart wearables or displays. The identification of the underlying physical effects governing the electrooptical characteristics, especially efficiency, and their dependency on LED emission wavelength and operation current is the focus of this work.
A physical model describing the current-voltage characteristics of modern blue LEDs is developed. This model correlates the LED voltage with its internal recombination dynamics and thus enables the prediction of the LED efficiency out of purely electrically acquired key figures.
The physical root cause for the efficiency decrease of blue and green LEDs towards higher currents was intensively debated in the literature for many years. In this work a concept to visualize Auger processes is developed. This way, it can be shown that the high current efficiency decrease, also known as Droop, can be attributed to Auger recombination.
Based on this conclusion a new concept to mediate the Droop is shown: By employing three-dimensional hole injecting layers in the epitaxial structure, the carrier transport can be improved, which is a lever to decrease the Droop.:1 Einleitung
2 Grundlagen
3 Exemplarische Herleitung grundlegender Kenngrößen einer typischen LED
4 Effizienzuntersuchungen an SQWs unterschiedlicher Wellenlänge
5 Untersuchung der Kleinstromeffizienz
6 Der Droop – Untersuchung des Hochstromverlustkanals
7 Verminderung des Droops - V-förmige Defekte zur Löcherinjektion
8 Zusammenfassung
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Optical and structural properties of systems of conjugated molecules and graphenesLange, Philipp 07 April 2014 (has links)
Systeme aus konjugierten Molekülen und Graphenen bergen hohes Potential für Anwendungen. Die Untersuchung ihrer Wechselwirkungsmechanismen ist wichtig für die Entwicklung neuer Anwendungen und Fokus dieser Arbeit: Optische Mikroskopie, Spektroskopie und Rasterkraftmikroskopie werden komplementär verwendet, um die optischen und strukturellen Eigenschaften solcher Systeme zu erforschen. Insbesondere werden (i) die Permeationsbarriere-Eigenschaften von Graphen in-situ auf einem halbleitenden Polymerfilm quantifiziert. Weiterhin werden (ii) die Fluoreszenz- und (iii) Raman-Emission von konjugierten Molekülen in der Nähe von Graphen untersucht und die entsprechenden Kopplungsmechanismen diskutiert. (i) Graphene zeigen sich als effizienter Schutz des empfindlichen Polymers [Poly(3-hexylthiophen)] vor Degeneration durch Sauerstoff und Wasser aus der Umgebungsluft. Dies legt nahe, dass Graphene nicht nur als transparente Elektrode, sondern gleichzeitig als Barriereschicht in künftigen optoelektronischen Bauelementen dienen können. (ii) Es wird gezeigt, dass die bekannten optischen Eigenschaften von Graphen die Existenz stark lokalisierter Graphen-Plasmonen im Sichtbaren implizieren. Durch Verwendung von nanoskaligen Emittern [Rhodamin 6G (R6G)], welche die für effiziente Anregung von Graphen-Plasmonen im optischen Frequenzbereich notwendigen großen Wellenvektor bereitstellen, wird Graphen-Plasmonen-induzierte (GPI) Fluoreszenz-Anregungsverstärkung von nahezu 3 Größenordnungen nachgewiesen. Demnach ist Graphen für plasmonische Bauelemente im Sichtbaren interessant. (iii) Außerdem wird GPI Verstärkung des Raman-Querschnittes von R6G um 1 Größenordnung nachgewiesen. Zukünftige Entwicklung von Antennen für zusätzliche direkte Anregung von Graphen-Plasmonen aus dem Fernfeld macht Graphen vielversprechend für leistungsfähige oberflächenverstärkte Raman-Spektroskopie. Zusammenfassend wurden neue und anwendungsrelevante Einblicke in die analysierten Systeme gewonnen. / Systems of conjugated molecules and graphenes bear high application potential. The investigation of their interaction mechanisms is important for design of new applications and the focus of this thesis: Optical microscopy, spectroscopy and scanning force microscopy are complementarily used to explore the optical and structural properties of such systems. In particular (i) the permeation barrier properties of graphene are quantified in-situ on a semiconducting polymer film. Furthermore (ii) the fluorescence and (iii) Raman emission of conjugated molecules in proximity to graphene are investigated and the respective coupling mechanisms are discussed. (i) Graphenes are found to efficiently protect the sensitive polymer [poly(3-hexylthiophene)] from degradation by oxygen and water from the ambient atmosphere. This suggests that graphenes can not only serve as transparent electrode, but simultaneously as a barrier layer in future optoelectronic devices. (ii) It is shown that the known optical properties of graphene imply the existence of strongly localized graphene plasmons in the visible. Using nanoscale emitters [rhodamine 6G (R6G)] that provide the high wave vectors necessary to efficiently excite graphene plasmons at optical frequencies, graphene plasmon induced (GPI) fluorescence excitation enhancement by nearly 3 orders of magnitude is demonstrated. Graphene is thus interesting for plasmonic devices in the visible. (iii) In addition GPI enhancement of the Raman cross section of R6G by 1 order of magnitude is demonstrated. The future design of antennas for additional direct farfield excitation of graphene plasmons makes graphene promising for powerful surface enhanced Raman spectroscopy. In summary new and application relevant insights were gained into the studied systems.
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Proposta e implementação de um receptor optoeletrônico integrado para redes ópticas passivas (PONs) empregando multiplexação por divisão de comprimento de onda (WDM) / Proposal and implementation of a optoelectronic integrated receiver for passive optical networks (PONs) employing wavelength division multiplexing (WDM)Manfrin, Stilante Koch 01 July 2003 (has links)
O presente trabalho descreve o desenvolvimento e implementação de duas configurações distintas de um receptor optoeletrônico integrado. A primeira configuração é similar a um projeto encontrado na literatura mas apresenta diversas modificações que lhe conferiram melhor desempenho em comparação ao projeto original. A segunda configuração é uma nova proposta deste trabalho. O receptor foi desenvolvido e implementado visando sua aplicação em redes de comunicações ópticas passivas (PONs) de alta velocidade comutadas a pacote, para possibilitar a utilização da técnica de multiplexação em comprimento de onda (WDM), aumentando assim a capacidade de transmissão da rede, em particular no ramo de ligação da rede de serviços com o usuário final, denominado rede de acesso. O principal objetivo do receptor aqui desenvolvido foi proporcionar uma sintonia rápida entre os canais disponíveis na rede, possibilitando sua seleção num tempo inferior àquele necessário para a transmissão de um único pacote de informação, diminuindo assim o atraso de sintonia e, por conseguinte, a perda de informação. Para tanto, os circuitos integrados implementados e caracterizados referem-se aos circuitos de chaveamento eletrônico e do amplificador de transimpedância das duas configurações investigadas. Os dados experimentais obtidos para as duas configurações confirmaram a previsão de chaveamento dos canais de entrada num intervalo de tempo da ordem de alguns nanosegundos, o que é totalmente compatível com a velocidade de transmissão das aplicações a que se destina este receptor (aproximadamente 5 Gbits/s). Adicionalmente, são apresentados os dados experimentais relativos à freqüência de corte, ganho direto, isolação, relação on/off e características de ruído dos circuitos implementados. / The present work describes the design and implementation of two configurations of an integrated optoelectronic receiver. The first one is similar to a previously reported design but with some modifications to improve its performance. The second one is a new proposal of this work. The goal of the receiver design and implementation was its application in high bit rate packet-switched passive optical networks (PONs) employing the wavelength division multiplexing (WDM) technique to increase the network capacity, in particular on the connection branch of the network core with the final user, the access network. The main goal of the receiver design was to achieve a fast channel tuning, allowing a tuning time smaller than the required for the transmission of a single information packet, decreasing the tuning latency and, therefore, the rate of information packet loss. In order to accomplish this goal, the implemented and tested integrated circuits include the electronic switching circuit and the transimpedance amplifier for both configurations investigated. The measured data for both configurations confirm the expected input channel switching time results, of about a few nanoseconds, which is certainly useful for the expected bit rate of operation (approximate 5 Gbps). Additionally, experimental results concerning cutoff frequency and bandwidth, direct gain, isolation, on/off ratio, and noise characteristics of both implemented circuits are presented.
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台灣光電企業跨足綠能整合之策略布局 / The transformation strategy of Taiwan's optoelectronic company to the green energy integration industry魏明皓, Wei, Ming Hao Unknown Date (has links)
台灣光電產業為近年來台灣經濟成長的最佳動力來源之一,截至2010年,台灣光電總產值已經突破新台幣2兆元。其中以LED、顯示面板、太陽能電池模組等貢獻最多,帶給台灣大量的就業機會,並創造出全球第一的產值。然而,台灣光電大廠以往的經營模式大都以OEM/ODM為主,製造代工屬微笑曲線價值最低的中間區域,因此企業不斷找尋轉型的機會。近年來因能源耗竭隱憂,綠能產業蔚為未來科技革命的新主流,如太陽能發電、風力發電、LED照明、電動車等,為台灣光電大廠創造新的契機。幾間光電領導大廠紛紛跨入綠能產業,除了研發製造端,也開始嘗試挑戰下游的系統整合與行銷通路,尤其以太陽能發電系統為主。面對下游不熟悉的領域,以及眾多的綠能廠商競爭對手,光電企業必須從自身核心能耐出發,找尋最佳切入點,並靈活運用相關資源,與事業夥伴密切合作,方能找到自己的定位,建立獨特競爭優勢。
本研究從光電企業跨足綠能產業的先後整體性策略布局進行分析比較,並由顧客價值與企業核心能力的角度出發,深入探討面對綠能產業下游的新事業之組織設計、營運模式、關鍵資源、關鍵流程等。本研究建議台灣光電廠商面對市場白地時,應打破傳統製造思維,以創新商業模式進行在地化資源整合,進而建立行銷通路,打造自有品牌。並且建構良好的學習交流管道,讓新事業在下游的經營管理經驗帶回企業。 / Recently, the optoelectronic industry becomes one of the driving forces of economic growth in Taiwan. Until 2010, the output value of optoelectronic industry was over 2000 billion NTD, creating many employment opportunities. The optoelectronic industry in Taiwan is accounted for the largest output value in the world, especially in sectors such as LED, photovoltaic panels, solar cell and solar modules.
However, a lot of optoelectronic companies in Taiwan are OEM/ODM based. They capture the lowest value in the supply chain. Hence, many companies are eager to seize the opportunity to implement transformation strategy. Nowadays, due to energy depletion issue, more and more people care about the popularized green energy industry, include solar power, wind power, LED lighting, electric cars and so on. This condition states good foundation for optoelectronic companies in Taiwan to perform transformation strategy. Some leading companies started to cross boundaries into the green energy industry, especially focusing on manufacturing and system integration of solar power system. Facing the unfamiliar downstream business and existing green energy competitors, optoelectronic companies should start with own core capability to find the best point of entry while entering the whole new industry. They need to integrate local resources and cooperate with business partners, finding their unique position and to build up their own competitive advantage.
This study analyzes a comprehensive strategy framework for optoelectronic companies in Taiwan crossing over to the green energy industry. First thing ahead, the company should start with its own core capability and consumer value, developing new business model, organization structure, key resources and key process of the new field. The conclusion of this research suggests that optoelectronic companies in Taiwan should forgo its old ways of manufacturing thinking, and operate with innovative business model to integrate the localized resources, establish its own marketing channel, create its own brand, and construct good learning process that can bring downstream experience into the organization when operating in the new industry.
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A DSP embedded optical naviagtion systemGunnam, Kiran Kumar 30 September 2004 (has links)
Spacecraft missions such as spacecraft docking and formation flying require high precision relative position and attitude data. Although Global Positioining Systems can provide this capability near the earth, deep space missions require the use of alternative technologies. One such technology is the vision-based navigation (VISNAV) sensor system developed at Texas A&M University. VISNAV comprises an electro-optical sensor combined with light sources or beacons. This patented sensor has an analog detector in the focal plane with a rise time of a few microseconds. Accuracies better than one part in 2000 of the field of view have been obtained. This research presents a new approach involving simultaneous activation of beacons with frequency division multiplexing as part of the VISNAV sensor system. In addition, it discusses the synchronous demodulation process using digital heterodyning and decimating filter banks on a low-power fixed point DSP, which improves the accuracy of the sensor measurements and the reliability of the system. This research also presents an optimal and computationally efficient six-degree-of-freedom estimation algorithm using a new measurement model based on the attitude representation of Modified Rodrigues Parameters.
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Studies On The Growth And Characterization Of II-VI Semiconductor Nanostructures By Evaporation MethodsYuvaraj, D 07 1900 (has links)
In recent years, there has been growing interests on II-VI semiconductor nanostructures, which are suitable for applications in electronics and optoelectronic devices such as solar cells, UV lasers, sensors, light emitting diodes and field emission displays. II-VI semiconductor nanostructures with different morphologies such as wires, belts, rods, tubes, needles, springs, tetrapods, plates, hierarchical structures and so on, have been widely grown by vapor transport methods. However the process conditions used for the growth of nanostructures still remains incompatible for device fabrication. The realization of practical nanoscale devices using nanostructured film depends mainly on the availability of low cost and lower processing temperatures to manufacture high purity nanostructures on a variety of substrates including glass and polymer.
In this thesis work, studies have been made on the growth and characterization of II-VI semiconductor nanostructures prepared at room temperature, under high vacuum, without employing catalysts or templates.
(i) ZnO nanostructured films with different morphology such as flowers, needles and shrubs were deposited at room temperature on glass and polymer substrates by plasma assisted reactive process. (ii) Zn/ZnO core/shell nanowires were grown on Si substrates under optimized oxygen partial pressure. Annealing of this core shell nanowire in high vacuum resulted in the formation of ZnO nanocanals. (iii) ZnS and ZnSe nano and microstructures were grown on Si substrates under high vacuum by thermal evaporation. The morphology, structural, optical properties and composition of these nano and microstructures were investigated by XRD, SEM, TEM, Raman, PL and XPS. The growth mechanism behind the formation of the different nanostructures has been explained on the basis of vapour-solid (VS) mechanism.
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Physical Design of Optoelectronic System-on-a-Chip/Package Using Electrical and Optical Interconnects: CAD Tools and AlgorithmsSeo, Chung-Seok 19 November 2004 (has links)
Current electrical systems are faced with the limitation in performance by the electrical interconnect technology determining overall processing speed. In addition, the electrical interconnects containing many long distance interconnects require high power to drive. One of the best ways to overcome these bottlenecks is through the use of optical interconnect to limit interconnect latency and power.
This research explores new computer-aided design algorithms for developing optoelectronic systems. These algorithms focus on place and route problems using optical interconnections covering system-on-a-chip design as well as system-on-a-package design. In order to design optoelectronic systems, optical interconnection models are developed at first. The CAD algorithms include optical interconnection models and solve place and route problems for optoelectronic systems. The MCNC and GSRC benchmark circuits are used to evaluate these algorithms.
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A DSP embedded optical naviagtion systemGunnam, Kiran Kumar 30 September 2004 (has links)
Spacecraft missions such as spacecraft docking and formation flying require high precision relative position and attitude data. Although Global Positioining Systems can provide this capability near the earth, deep space missions require the use of alternative technologies. One such technology is the vision-based navigation (VISNAV) sensor system developed at Texas A&M University. VISNAV comprises an electro-optical sensor combined with light sources or beacons. This patented sensor has an analog detector in the focal plane with a rise time of a few microseconds. Accuracies better than one part in 2000 of the field of view have been obtained. This research presents a new approach involving simultaneous activation of beacons with frequency division multiplexing as part of the VISNAV sensor system. In addition, it discusses the synchronous demodulation process using digital heterodyning and decimating filter banks on a low-power fixed point DSP, which improves the accuracy of the sensor measurements and the reliability of the system. This research also presents an optimal and computationally efficient six-degree-of-freedom estimation algorithm using a new measurement model based on the attitude representation of Modified Rodrigues Parameters.
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Propriétés électriques du ZnO monocristallin / Electrical properties of ZnO single crystalBrochen, Stéphane 13 December 2012 (has links)
L’oxyde de zinc ZnO, est un semiconducteur II-VI très prometteur pour les applications en opto-électronique dans le domaine UV, notamment pour la réalisation de dispositifs électroluminescents (LED). Les potentialités majeures du ZnO pour ces applications résident notamment dans sa forte liaison excitonique (60 meV), sa large bande interdite directe (3.4 eV), la disponibilité de substrats massifs de grand diamètre ainsi que la possibilité de réaliser des croissances épitaxiales de très bonne qualité en couches minces ou nano structurées (nanofils). Néanmoins, le développement de ces applications est entravé par la difficulté de doper le matériau de type p. L'impureté permettant d'obtenir une conductivité électrique associée à des porteurs de charges positifs (trous), et donc la réalisation de jonctions pn à base de ZnO, n'a pas encore été réellement identifiée. C'est pourquoi une des étapes préliminaires et nécessaires à l'obtention d'un dopage de type p fiable et efficace, réside dans la compréhension du dopage résiduel de type n, ainsi que des phénomènes de compensation et de passivation qui sont mis en jeu au sein du matériau. La maîtrise de la nature des contacts (ohmique ou Schottky) sur différentes surfaces d'échantillons de ZnO nous a permis dans ce but de mettre en œuvre à la fois des mesures de transport (résistivité et effet Hall) et des mesures capacitives (capacité-tension C(V), Deep Level Transient Spectroscopy (DLTS) et Spectroscopie d'admittance).Dans un premier temps, nous avons donc cherché à comprendre de manière approfondie les propriétés électriques du ZnO massif. Nous avons ainsi étudié le rôle des défauts profonds et peu profonds sur la conductivité des échantillons, aux travers de différents échantillons massifs obtenus par synthèse hydrothermale ou par croissance chimique en phase vapeur. Nous avons également étudié l'impact de la température de recuits post-croissance, sur les propriétés de transport des échantillons. A la lumière des résultats obtenus sur le dopage résiduel de type n des échantillons de ZnO massifs, nous avons ensuite procédé à différents essais de dopage de type p du ZnO par implantation ionique d'azote et par diffusion en ampoule scellée d’arsenic. L'impureté azote a été choisie dans le cadre d'une substitution simple de l'oxygène qui devrait permettre de créer des niveaux accepteurs dans la bande interdite du ZnO. Nous avons également étudié l'impureté arsenic, qui selon un modèle théorique peut former un complexe qui permet d'obtenir un niveau accepteur plus proche de la bande de valence que le niveau. Outres les études réalisées sur les échantillons de ZnO massif et les essais de dopage de type p, nous avons également étudié les propriétés électriques d'échantillons de ZnO monocristallins sous forme de couches minces obtenues par croissance en phase vapeur d’organométalliques, dopées intentionnellement ou non. Les corrélations entres les mesures SIMS et C(V) nous ont permis notamment de mettre en évidence une diffusion et un rôle très importante de l'aluminium sur les propriétés électriques des couches minces de ZnO épitaxiées sur substrat saphir.Dans le cadre de cette thèse nous avons réussi à clarifier les mécanismes du dopage de type n, intentionnel ou non intentionnel, dans le ZnO monocristallin. Nous avons également identifié les impuretés et les paramètres de croissance importants permettant d'obtenir un dopage résiduel de type n le plus faible possible dans les couches épitaxiées. Cette maitrise du dopage résiduel de type n est une étape préliminaire indispensable aux études de dopage de type p car elle permet de minimiser la compensation des accepteurs introduits intentionnellement. Cette approche du dopage sur des couches minces de ZnO dont le dopage résiduel de type n est très faible apparait comme une voie très prometteuse pour surmonter les problèmes d'obtention du dopage de type p. / Zinc oxide (ZnO) is a II-VI semiconductor which appears as a very promising material for UV opto-electronic applications, in particular for the production of light emitting devices (LED). For these applications, ZnO presents strong advantages as a high exciton binding energy (60 meV ), a wide direct band gap (3.4 eV), the availability of large diameter bulk substrates for homoepitaxial growth of high quality thin films or nanostructures. However, the development of these applications is hampered by the difficulty to dope ZnO p-type. The impurity leading to an electrical conductivity associated with positive charge carriers (holes), and therefore the production of ZnO pn junctions have not yet been really identified.In this thesis we have studied the physical mechanisms that govern the electrical properties of ZnO single crystal and epilayers. The control of contacts (ohmic or Schottky) on different ZnO surfaces allowed us to carry out both transport measurements (resistivity and Hall effect) and capacitance measurements (C(V), Deep Level Transient Spectroscopy (DLTS) and admittance spectroscopy).At first, we have studied the role of deep and shallow defects on the n-type conductivity of bulk ZnO samples obtained by Hydrothermal synthesis (HT) or by Chemical Vapor Transport (CVT). We also investigated the impact of post-growth annealing at high temperature under oxygen atmospheres on the transport properties of samples. Thanks to the previous results on the residual n-type doping, we have reported on several attempts to obtain p-type ZnO. We have discussed the potential of different candidates for the achievement of p-type doping and present our tentative experiments to try and demonstrate the reality, the ability and the stability of p-type doping by nitrogen implantation and arsenic diffusion. The nitrogen impurity has been chosen for oxygen substitution, which should allow the creation of acceptor levels in the ZnO band gap. We also studied arsenic as a potential p-type dopant, according to a model whereby arsenic substitutes for oxygen and, if associated with two zinc vacancies, forms a complex with a shallower ionization energy than in the case of direct oxygen substitution.In addition to the studies on bulk ZnO samples and attempts on p-type doping, we have also studied the electrical properties of thin film ZnO samples obtained by Metal Organic Vapor Phase Epitaxy, either intentionally or unintentionally doped. Correlations between SIMS and C(V) measurements allowed us to highlight especially the importance of aluminum as a residual impurity in epitaxial layers grown on sapphire substrates.In this thesis we have clarified intentional or unintentional n-type doping mechanisms in ZnO single crystal samples. We have also identified impurities and growth parameters responsible for the residual n-type doping. This understanding is a crucial and preliminary step for understanding the doping mechanisms at stake in this material and is also necessary to achieve stable p-type conductivity, which is still the main challenge for the realization of optoelectronic devices based on ZnO.
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