Proximity effect in planar Superconductor/Semiconductor junction

We have measured the very low temperature (down to 30 mK) subgap resistance of Titanium Nitride (Superconductor, Tc = 4.6 K)/highly doped Silicon (Semiconductor) SIN junction (the insulating layer stands for the Schottky barrier). As the temperature is lowered, the resistance increases as expected in SIN junction. Around 300 mK, the resistance shows a maximum and decreases at lower temperature. This observed behavior is due to coherent backscattering towards the interface by disorder in Silicon ("Reflectionless tunneling"). This effect is also observed in the voltage dependence of the resistance (Zero Bias Anomaly) at low temperature (T<300 mK). The overall resistance behavior (in both its temperature and voltage dependence) is compared to existing theories and values for the depairing rate, the barrier resistance and the effective carrier temperature are extracted.Comment: Submitted to LT22, Helsinki - August 1999, phbauth.cls include

Dispositifs électrooptique assistés plasmon en silicium

Bien que les propriétés optiques des métaux nanostructurés soit connues depuis de nombreuses décennies, ce n'est que dans les dernières années que ce domaine a suscité un grand intérêt. Ceci est en partie dû aux nombreux progrès des techniques de nanofabrication. Le domaine de la plasmonique est souvent présentée comme la support de la prochaine génération de dispositifs de traitement de l'information, mélageant la nanoélectronique et la photonique silicium pour obtenir des disposotifs plus performants. Les systèmes microélectroniques actuels approchant de la saturation en terme de bande passante et de consomation énergétique, la migration vers les systèmes photoniques semble inévitable. La prédiction de la réponse électromagnétique de ces composants nano-photoniques est essentiels au succès de leur intégration réaliste. Les outils numériques de simulation électromagnétiques sont le moyen par excellence de calculer précisement er de manière réaliste les propriétés optiques de composants nanophotoniques, et en particulier ceux utilisant des plasmons de surface. Ce travail de thèse rend compte de l'analyse numérique de la propagation et des caractéristiques de champ proche de composants à base de plasmons pour la photonique en technologie CMOS. Les deux principaux outils de modélisation EM utilisés à cet égard sont la méthode des éléments des moments, ainsi que la FDTD. Deux types principaux de dispositifs actifs plasmoniques actifs ont été étudiés: d'une part les modulateurs électro-optiques intégrés et d'autre part des détecteurs à base de quantum dot de Ge, le tout dans la gamme du proche infrarouge. La question cruciale d'un couplage efficace de la lumière dans un mode très confiné plasmonique a d'abord été étudiée de manière à isoler la part modale des principales contributions. Ensuite, une nouvelle structure de modulateur assisté plasmon a été proposée et une conception optique complète prenant en compte les contraintes technologiques d'une fonderie CMOS est proposée et discutée. Enfin une conception optimisée du couplage radiatif de l'absorption d'un point de Ge, en utilisant une antenne dipolaire plasmonique, est étudiée. En particulier, l'ingénierie radiative du substrat SOI permet de démontrer un effet considérable sur la performance finale du dispositif.Interest in the eld of plasmonics has been primarily driven by the need to guide and con ne light in the subwavelength scale. The past few years has witnessed a huge interest in this eld largely due to the may advances that have occured in nanofabrication techniques. The eld of plasmonics is often touted as the next generation platform that could interface nanoscale electronics and Si photonics. With current electronic systems nearing saturation, the migration to photonic systems would become inevitable. Crucial to achieving this integration is to design reliable plasmonic components within nanophotonics circuits. This however requires an accurate estimation of the electromagnetic response of these components. Numerical modeling tools are one way to gauge this response. By and large the thesis deals with numerically analysing the propagation and near eld characteristics of plasmon based components for Si photonics. The two principal EM modelling tools used in this regard are the boundary element method as well as the nite di erence time domain.Two main kind of active plasmonic active devices were investigated: integrated modulators, and free space radiation photodetectors. The critical issue of an e cient coupling of light into a very con ned guided plasmonic mode was rst investigated so as to isolate the main modal governing contributions. Next, a new structure of plasmon assisted modulator was proposed and a complete optical design taking into the technological constraints of a CMOS foundry is provided and discussed. Finally a design optimizing the radiative coupling to the absorption of a Ge dot, using a plasmonic dipolar antenna, is studied. In particular the radiative engineering of the supporting SOI substrate is shown to have a tremendousSAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Dopant-controlled single-electron pumping through a metallic island

We investigate a hybrid metallic island / single dopant electron pump based on fully-depleted silicon on insulator technology. Electron transfer between the central metallic island and the leads is controlled by resonant tunneling through single phosphorus dopants in the barriers. Top gates above the barriers are used control the resonance conditions. Applying radio frequency signals to the gates, non-adiabatic quantized electron pumping is achieved. A simple deterministic model is presented and confirmed by comparing measurements with simulations

Transport électronique à travers deux dopants, en régime statique et dynamique dans des transistors silicium

Dans cette thèse, nous nous sommes intéressés à l'étude à basse température de dispositifs en silicium de taille nanométrique. Dans ces dispositifs, il est possible de faire passer le courant électrique à travers un nombre réduit de dopants. Nous avons étudié plus spécifiquement le cas de deux dopants en séries, dont les potentiels électrostatiques sont contrôlés indépendamment par deux tensions de grille. En régime de transport électronique statique, il est possible d'effectuer une spectroscopie des niveaux électronique des dopants. On mesure la séparation des deux premiers états de dopants phosphore, qui est proche de 10 meV, alors qu'elle est de 11,7 meV pour des dopants dilués dans un cristal massif. Cette différence s'explique par la proximité des dopants avec une interface avec de l'oxyde de silicium. En régime dynamique, lorsque les niveaux des dopants sont modulés par un signal périodique, on observe qu'un courant est généré par le dispositif. L'évolution du courant en fonction des tensions de grille est simulée en prenant en compte les couplages tunnels du système. À haute fréquence, lorsque l'on observe la quantification d'énergie électromagnétique échangée avec le système, on reproduit le courant mesuré en fonction de l'amplitude du signal appliqué sur les grilles. Cette mesure permet de mettre en évidence la cohérence d'un électron partagé sur deux dopants.In this thesis, we studied low temperature silicon devices of nanometer size. In these devices, an electric current can flow through a small number of dopants. We studied the case of two dopants in series which electrostatic potentials are controlled independently by two gate voltages. In static regime, it is possible to perform spectroscopy of electronic doping levels. We measure an energy separation of the first two states for the phosphorus dopants around 10 meV, while this separation is 11.7 meV for dopants diluted in a bulk crystal. This difference is explained by the proximity of dopants with a silicon oxide interface. When the levels of the dopants are modulated by a periodic signal a current is generated by the device. The evolution of the current versus gate voltages is simulated by taking into account the tunnel couplings of the system. At high frequency, when we observe the quantification of electromagnetic energy exchanged with the system, the measured current as a function of the amplitude of the signal applied to the gates is described. This is an experimental evidence of the coherence of an electron shared by two dopants.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Pauli Blockade in a Few-Hole PMOS Double Quantum Dot limited by Spin-Orbit Interaction

We report on hole compact double quantum dots fabricated using conventional CMOS technology. We provide evidence of Pauli spin blockade in the few hole regime which is relevant to spin qubit implementations. A current dip is observed around zero magnetic field, in agreement with the expected behavior for the case of strong spin-orbit. We deduce an intradot spin relaxation rate $\approx$120\,kHz for the first holes, an important step towards a robust hole spin-orbit qubit

Switching quantum transport in a three donors silicon fin-field effect transistor

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Design of the citadel of Bonifacio urban area through experimental and numerical assessment of pedestrian comfort

International audienceThis paper presented a study on the optimization of the pedestrian comfort in the citadel of Bonifacio, the windiest city of Europe. Urbalterre, the urban architect agency in charge of the project combined Wind Tunnel and CFD simulations to assess and optimize the pedestrian wind comfort. The first step was an evaluation of the wind statistics at the district location. Weather data from the nearest weather station was extrapolated to Bonifacio using CFD simulations on a domain of several kilometers to take into account the local orography and roughness. The design of the district was then performed in three steps. A first assessment was carried out in wind tunnel using Particle Image Velocimetry. To our knowledge, very few studies used this type of measurements to assess wind comfort. This kind of measurements indeed requires special care to obtain sufficient accuracy due to the proximity of the laser sheet from the ground. Velocity measurements were combined with weather data to compute a wind comfort criterion. Results highlighted severe comfort issues which require an optimization of the district. A second step consists of optimization carried out by the urban architects of Urbalterre themselves thanks to the UrbaWind CFD solution. Good correlations between wind tunnel and CFD results were observed. On some locations, CFD results presented lower wind mean speed values for some Venturi effects compared to the wind tunnel results. CFD tool allowed the urban architects to iterate several versions of the district and to convergence towards an optimal solution. The use of vegetation leads to an optimized version of the district which was finally tested again in the wind tunnel. Final adjustments were performed directly in the wind tunnel using PIV measurements to optimize a Venturi effect between two buildings. The main interest of this study is the combination of PIV measurements, which proved to be a very efficient tool to assess wind comfort in wind tunnel, and CFD simulations which were carried out by the urban architects themselves to iterate various solutions. The configuration of the Montlaur Citadel, due its location above 60m cliffs and the impressive statistics of the wind blowing on the South of Corsica Island, was a tough challenge regarding the optimization of pedestrian wind comfort. Again, the use of the vegetation has proven to be one of the most efficient way to optimize pedestrian wind comfort when designing a urban area