Depuis sa découverte en 2004, le graphène n’a cessé de capter l’intérêt de la communauté scientifique grâce à ses innombrables propriétés et à la diversité de ses applications potentielles. Néanmoins, son implémentation à l’échelle industrielle exige encore beaucoup de contraintes et notamment concernant la stabilité de ses performances.L’objectif de cette thèse est de développer un procédé de fabrication de dispositifs intégrant une couche de graphène faiblement dopée et présentant des caractéristiques électriques stables. Le graphène, étant un matériau extrêmement sensible à l’environnement, il s’est avéré primordial de le protéger afin d’avoir un bon contrôle sur ses propriétés. Pour ce faire, plusieurs approches technologiques ont été abordées et analysées à l’aide d’une étude statistique des caractéristiques de plus de 500 transistors. Le procédé optimal intègre une couche de « protection » du graphène réalisée après son transfert et la passivation des dispositifs fabriqués avec une couche d’oxyde. Grâce à cette méthode, 75% des transistors fabriqués sont fonctionnels, présentent une faible hystérèse et sont stables dans le temps, ce qui constitue des critères indispensables pour l’intégration du graphène dans des composants discrets en particulier pour l’optoélectronique.Par la suite, le procédé technologique développé a été adapté à la fabrication de lignes coplanaires à base de graphène pour la photodétection hyperfréquence. Des valeurs de photo-courant, proches de celles de la littérature (0.15 mA/W), ont été mesurées avec un laser 1.55 µm modulé à des fréquences allant jusqu’à 40 GHz. Cette technologie est maintenant évaluée pour la fabrication de mixeurs optoélectroniques haute fréquence. / Since its discovery in 2004, graphene has attracted the attention of the scientific community due to its unique properties as well as the diversity of its potential applications. Nevertheless, its implementation at industrial scale still requires many challenges including its performance stability.The objective of my PhD is to develop a technological process for the fabrication of devices integrating low-doped graphene and exhibiting stable electrical characteristics. As graphene is extremely sensitive to the environment, it is crucial to protect its surface to accurately control its properties. To do this, several technological approaches have been analyzed using the statistical characteristics of more than 500 transistors. The optimal process integrates a “protection” layer after graphene transfer and the passivation of the fabricated devices with an oxide layer. 75% of the passivated transistors were functional, with low hysteresis and time-stable performances. These criteria are essential for the integration of graphene in discrete components, in particular for optoelectronic devices.Subsequently, the technological process developed was adapted for the fabrication of graphene based coplanar waveguides for high frequency photodetection. We report on a measured photocurrent of 0.15 mA/W with a 1.55 µm laser modulated up to 40 GHz. This technology is currently studied for the fabrication of high frequency optoelectronic mixers

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Esta tese trata da modelagem das características eletrônicas de dispositivos semicondutores baseados em contatos Schottky heterodimensionais, definidos como contatos entre um metal e um sistema de dimensionalidade reduzida. Especificamente, este trabalho concentra-se na situação em que o metal é posto em contato direto com um gás eletrônico bidimensional presente na interface de uma heterojunção empregando dopagem modulada. Dispositivos de interesse são diodos Schottky, bem como estruturas do tipo metal-semicondutor-metal (MSM). Para a característica capacitância-tensão, C-V, é desenvolvido um modelo quasi-bidimensional que apresenta excelente concordância com os resultados experimentais disponíveis. Do ponto de vista da característica corrente-tensão, I-V, é apresentado um modelo unificado, considerando tanto o mecanismo de tunelamento, quanto o de emissão termoiônica. Nossas previsões teóricas, suportadas por alguns indicativos experimentais, sugerem que, para aplicações em fotodetecção, o uso de contatos heterodimensionais, substituindo junções metal-semicondutor convencionais, pode reduzir a corrente de escuro em pelo menos uma ordem de magnitude. / This thesis deals with the modeling of the electronic characteristics of semiconductor devices based on heterodimensional Schottky contacts, defined as contacts between a metal and a reduced dimensionality system. Specifically, this work focus on the situation in which a metal is placed in direct contact with a two dimensional electron gas located at the interface of a modulation doped heterojunction. Devices of interest are Schottky diodes as well as metal-semiconductor-metal (MSM) structures. For the capacitance-voltage characteristics a quasi two-dimensional model is developed, which yields very good agreement with available experimental results. For the current-voltage characteristics a unified model is presented, considering the tunneling as well as the thermionic emission mechanisms. Our theoretical predictions, supported by a few experimental findings, suggest that, for photodetection applications, the use of heterodimensional contacts, replacing conventional metal-semiconductor junctions, can reduce the dark current by at least one order of magnitude.

In this thesis, we demonstrate an array of photodetection theory and techniques bridging the traditional discrete and continuous variable experimental domains. In quantum optics, the creation and measurement of states of light are intertwined and we present experimental architectures considering both aspects. We describe the measurement of mean photon numbers at optical sideband frequencies using homodyne detection. We use our technique to provide a direct comparison to photon-counting measurements and observe that our technique exhibits superior speed, dynamic range and mode selectivity compared to photon counters. Our analysis also rejects a semiclassical description of the vacuum state, with our observations supporting the quantum mechanical model. We create a new means of describing the detection ???signatures??? of multi-port networks of non-photon-number discriminating detectors. Our model includes the practical effects of loss and dark counts. We use this model to analyse the performance of the loopand balanced- time-division-multiplexed detector architectures in a projective measurement role. Our analysis leads us to describe a prescriptive recipe for the optimisation of each architecture. In light of contemporary technology, we conclude the balanced TDM detector is the better architecture. Our analysis is then extended to the tomographic reconstruction of an unknown optical state using multi-port photon-counting networks. Our new approach is successfully applied to the reconstruction of the photon statistics of weak coherent states and demonstrates reduced error and sensitivity to experimental parameter variations than established techniques. We report the development of a source of quadrature squeezed vacuum at 1550 nm, and characterise the squeezing observed at the first 3 free spectral ranges of the downconversion cavity. This is then used as a source of frequency-entangled photons for a projective photon subtraction operation described by our earlier theory. We propose a new hybrid time/frequency domain approach to homodyne detection and illustrate its application in characterising the prepared state. Our output state has a statistically significant single photon contribution and permits future experimentation in frequency basis quantum information.

Esta tese trata da modelagem das características eletrônicas de dispositivos semicondutores baseados em contatos Schottky heterodimensionais, definidos como contatos entre um metal e um sistema de dimensionalidade reduzida. Especificamente, este trabalho concentra-se na situação em que o metal é posto em contato direto com um gás eletrônico bidimensional presente na interface de uma heterojunção empregando dopagem modulada. Dispositivos de interesse são diodos Schottky, bem como estruturas do tipo metal-semicondutor-metal (MSM). Para a característica capacitância-tensão, C-V, é desenvolvido um modelo quasi-bidimensional que apresenta excelente concordância com os resultados experimentais disponíveis. Do ponto de vista da característica corrente-tensão, I-V, é apresentado um modelo unificado, considerando tanto o mecanismo de tunelamento, quanto o de emissão termoiônica. Nossas previsões teóricas, suportadas por alguns indicativos experimentais, sugerem que, para aplicações em fotodetecção, o uso de contatos heterodimensionais, substituindo junções metal-semicondutor convencionais, pode reduzir a corrente de escuro em pelo menos uma ordem de magnitude. / This thesis deals with the modeling of the electronic characteristics of semiconductor devices based on heterodimensional Schottky contacts, defined as contacts between a metal and a reduced dimensionality system. Specifically, this work focus on the situation in which a metal is placed in direct contact with a two dimensional electron gas located at the interface of a modulation doped heterojunction. Devices of interest are Schottky diodes as well as metal-semiconductor-metal (MSM) structures. For the capacitance-voltage characteristics a quasi two-dimensional model is developed, which yields very good agreement with available experimental results. For the current-voltage characteristics a unified model is presented, considering the tunneling as well as the thermionic emission mechanisms. Our theoretical predictions, supported by a few experimental findings, suggest that, for photodetection applications, the use of heterodimensional contacts, replacing conventional metal-semiconductor junctions, can reduce the dark current by at least one order of magnitude.

Les nanocristaux colloïdaux semi-conducteurs sont des matériaux synthétisés en suspension et dont les propriétés optiques sont ajustables par leur taille. Une fois sous forme de film, il est possible d’effectuer du transport de charges et ainsi obtenir des dispositifs opto-électroniques. Nous avons choisi deux types de nanocristaux présentant des propriétés optiques originales, mais dont le transport est mal connu. Nous l’étudions d’abord dans des films de nanocristaux bidimensionnels, les nanoplaquettes de CdSe, qui sont une réalisation colloïdale de puits quantiques. Nous montrons qu’il est possible d’accroître le gain de photoconduction en passivant les pièges électroniques afin d’augmenter le temps de vie des porteurs photogénérés. Nous tirons également parti de l’extension latérale de ces objets en les déposant sur des électrodes nanométriques de la taille des particules. Cela permet de s’affranchir du transport par sauts tunnel tout en surmontant l’interaction coulombienne entre l’électron et le trou photogénérés. De manière alternative, nous utilisons un canal de graphène comme couche de transport. Combiné aux propriétés optiques bien définies des nanoplaquettes, nous associons ainsi le meilleur des deux mondes. Enfin, nous étudions le transport dans des films de nanocristaux de HgSe. Ces objets étant naturellement dopés après synthèse, ils présentent une transition intrabande dans l’infrarouge moyen. Nous montrons que le dopage peut s’expliquer par la réduction des nanocristaux par l’eau, et qu’il est contrôlable en jouant sur les dipôles de surface induits par les ligands. Cela nous permet finalement d’élaborer un photodétecteur sur un substrat flexible. / Colloidal semiconducting nanocrystals are solution-grown inorganic particles whose optical properties are size-dependent. By depositing a film of these objects, charge transport become possible and one can obtain optoelectronic devices. We have chosen two types of nanocrystals with original optical properties, but whose transport is poorly understood and requires studying. First, we study it in films of two-dimensional materials, the CdSe nanoplatelets. These are colloidal realization of quantum wells. We show that it is possible to amplify the photoconductive gain by passivating electronic traps, thus increasing the photogenerated carriers lifetime. We also take advantage of the lateral extension of these objects by depositing them on nanoscale electrodes of the size of the particles. This eliminates the hopping transport while overcoming the coulombic interaction between the photogenerated electron and hole. Alternatively, we use a graphene channel as a transport layer. Together with the well defined optical properties of nanoplatelets, we associate the best of both materials. Finally, we study the transport in films of HgSe nanocrystals. Being naturally doped after synthesis, these objects exhibit an intraband transition in the mid-infrared range. We show that the doping can be explained by the water reduction of nanocrystals, and is controllable by varying the ligandsinduced surface dipoles. This allows us eventually to develop a photodetector on a flexible substrate.

La croissance sans cesse de la demande des débits de données élevés durant ces dernières décennies, soutenue par le déploiement des réseaux optiques permettant un débit de l’ordre de plusieurs Gbit/s a conduit naturellement vers l’intérêt de développement des applications à 60 GHz dans les réseaux locaux. Des normes telles que l’IEEE 802.15.3c et IEEE 802.11ad pour la transmission sans fil en bande millimétrique ont été proposées. A de telles fréquences, les pertes en espace libre sont très élevées et les ondes radios ne traversent pas les murs. Les liaisons radio sur fibre (RoF), utilisées comme déport optique d’une pièce vers une autre, permettent ainsi la distribution des signaux très haut débit dans toute la maison ou dans l’ensemble du bâtiment, en palliant le défaut de faible distance de propagation en espace libre. L’accès, par la modélisation des circuits électriques équivalents de chacun des composants du système considéré, à la simulation de ces systèmes RoF permet une optimisation du système en termes de qualité de transmission. Ainsi, les caractéristiques optiques et électriques des composants constituant les systèmes RoF sont étudiées et analysées conjointement ce qui offre la possibilité de la conception de circuits intégrés photonique-RF. Cette thèse concerne l’étude et simulation des liaisons RoF à l’aide de circuits électriques équivalents de composants photoniques. Cette étude est destinée aux applications sans fil à 60 GHz de grande bande passante permettant un très haut débit de transmission. La technique de modulation d’intensité directe ou externe et détection directe est privilégiée à une fréquence intermédiaire afin d’assurer la simplicité et le bas coût du système. Le signal radio est ensuite transposé sur une porteuse dans la bande 60 GHz. Dans un premier temps, pour valider les modèles des circuits électriques équivalents développés, les caractéristiques mesurées des composants optoélectroniques sont comparées aux résultats de simulation. Ensuite, l’étude de caractérisation est menée à l’échelle système par analyse des paramètres analogiques comme le gain, le bruit et non-linéarité. La dynamique de différentes liaisons RoF peut ainsi être déterminée. La transmission des signaux numériques complexes de type OFDM est finalement réalisée par une méthode de co-simulation numérique/analogique. La qualité de transmission est étudiée par évaluation de l’amplitude du vecteur d’erreur (EVM) des constellations des signaux numériques. L’étude est effectuée et validée dans un premier temps conformément à la norme ECMA-368 dédiée à la bande centimétrique et ensuite étendue à la bande millimétrique conformément à la norme IEEE 802.15.3c. Pour finir, l’effet du canal en espace libre à 60 GHz est considéré afin d’analyser la transmission de bout en bout / The growth continually demand of higher data rates in recent decades, supported by the deployment of optical networks allowing a flow of the order of several Gbit/s naturally leads to application development interest on 60 GHz local networks. Standards such as IEEE IEEE 802.15.3c and 802.11ad for millimeter-band wireless transmission have been proposed. At such frequencies, the free space loss is very high and the radio waves do not penetrate walls. The radio over fiber links (RoF), used as optical link from one room to another and enable the distribution of high-speed signals throughout the home or throughout the building, overcoming the failure for low distance free space propagation. Access, by modeling the electrical equivalent of each component of the system considered circuits, simulation of the RoF systems enables optimization of the system in terms of transmission quality. Thus, the optical and electrical characteristics of components of RoF systems are studied and analyzed together which offers the possibility of designing integrated photonic-RF circuits. This thesis concerns the study and simulation of RoF links using electrical equivalent circuits of photonic components. This study is intended for wireless applications at 60 GHz of bandwidth for a high transmission rate. The modulation technique of direct or external intensity and direct detection is preferred at an intermediate frequency in order to ensure simplicity and low cost of the system. The radio signal is then transposed onto a carrier in the band 60 GHz. First, to validate the models developed electrical equivalent circuit, the measured characteristics of optoelectronic components are compared with simulation results. Then, the characterization study is conducted to the scale by analysis of analog parameters such as gain, noise and non-linearity. The dynamics of different RoF links can thus be determined. Transmitting OFDM complex digital signal is finally achieved by a method of digital / analog co-simulation. The transmission quality has been studied by evaluation of the magnitude of the error vector (EVM) constellations digital signals. The study is conducted and validated as a first step in accordance with the ECMA-368 standard dedicated to the centimetric band and then spread to the millimeter band from IEEE 802.15.3c standard. Finally, the channel effect in free space at 60 GHz is considered to analyze the transmission end to end

MXenes, a new class of two-dimensional (2D) materials, have recently demonstrated impressive optoelectronic properties associated with its ultrathin layered structure. Particularly, Ti3C2Tx, the most studied MXene by far, was shown to exhibit intense surface plasmons (SPs), i.e. collective oscillations of free charge carriers, when excited by electromagnetic waves. However, due to the lack of information about the spatial and energy variation of those SPs over individual MXene flakes, the potential use of MXenes in photonics and plasmonics is still marginally explored. Hence, the main objective of this dissertation is to shed the light upon the plasmonic behavior of MXenes at the nanoscale and extend their use beyond their typical electrochemical applications. To fulfill our objective, we first elucidated the underlying characteristics governing the plasmonic behavior of MXenes. Then, we revealed the existence of various tunable SP modes supported by different MXenes, i.e. Ti3C2Tx and Mo2CTx, and investigated their energy and spatial distribution over individual flakes. Further, we fabricated an array of MXene-based flexible photodetectors that only operate at the resonant frequency of the SPs supported by MXenes. We also unveiled the existence of tunable SPs supported by another 2D nanomaterial (i.e. MoO2) and juxtaposed its plasmonic behavior with that of MXenes, to underline the uniqueness of the latter. Noteworthy, as in the case of MXenes, this was the first progress made on studying specific SP modes supported by MoO2 nanostructures. In this part of the dissertation, we were able to identify and tailor multipolar SPs supported by MoO2 and illustrate their dependence on their bulk band structure. In the end, we show that, on the contrary, SPs in MXenes are mainly controlled by the surface band structure. To confirm this, we selectively altered the subsurface band structure of Ti3C2Tx and modulated its work function (from 4.37 to 4.81 eV) via charge transfer doping. Interestingly, thanks to the unchanged surface stoichiometry of Ti3C2Tx, the plasmonic behavior of Ti3C2Tx was not affected by its largely tuned electronic structure. Notably, the ability to attain MXenes with tunable work functions, yet without disrupting their plasmonic behavior, is appealing to many application fields.