The study of waves and instabilities in quantum plasmas is of fundamental importance for understanding collective interactions in superdense astrophysical objects, in high intense laser-plasma/solid-matter interactions, in microelectronic devices and metallic nanostructures. In dense quantum plasmas, there are new pressure laws associated with the Fermi-Dirac distribution functions and new quantum forces associated with the quantum Bohm potential and the Bohr magnetization involving electron ½ spin. These forces significantly alter the collective behavior of dense quantum plasmas. This thesis contains six papers, considering several novel collective modes and instabilities at quantum scales. In Paper I, we have used the quantum hydrodynamical (QHD) model for studying the one-dimensional dust-acoustic (DA) waves incorporating the Fermi pressure law and the quantum Bohm potential. The latter modifies the DA wave dispersion relation in a collisional plasma. In Paper II, we have calculated the electrostatic potential of a test charge in an unmagnetized electron-ion quantum plasma. It is found that the Debye-Hückel and oscillatory wake potentials strongly depend upon the Fermi energy at quantum scales. The results can be of interest for explaining the charged particle attraction and repulsion in degenerate quantum plasmas, such as those in semiconductor and microelectronic devices. Paper III presents the parametric study of nonlinear electrostatic waves in two-dimensional collisionless quantum dusty plasmas. A reductive perturbation method has been employed to the QHD equations together with the Poisson equation, obtaining the cylindrical Kadomtsev-Petviashvili (CKP) equations and their stationary localized solutions. We have numerically examined the quantum mechanical and geometrical effects on the profiles of nonplanar quantum dust-ion-acoustic (DIA) and DA solitary waves. The role of static as well as mobile (negatively or positively charged) dust particles on the low-frequency electrostatic waves has also been highlighted for metallic nanostructures. Paper IV introduces the nonlinear properties of the ion-sound waves in a dense electron-ion Fermi magnetoplasma. The computational analysis of the nonlinear system reveals that the Sagdeev-like potential and the ion-sound density excitations are significantly affected by the wave direction cosine and the Mach number at quantum scales. Paper V considers the nonlinear interactions of electrostatic upper-hybrid (UH), ion-cyclotron (IC), lower-hybrid (LH), and Alfvén waves in a quantum magnetoplasma. The nonlinear dispersion relations have been analyzed analytically to obtain the growth rates for both the decay and modulational instabilities involving the dispersive IC, LH, and Alfvén waves. In Paper VI, we have identified a new drift-like dissipative instability in a collisional quantum plasma. The modified unstable drift-like mode can cause cross-field anomalous ion-diffusion at quantum scales.

Dans les dernières années, beaucoup de travail a été consacré par l’industrie électronique pour réduire la consommation d’énergie des composants micro-électroniques qui représente un fardeau important dans la spécification des nouveaux systèmes.Afin de réduire la consommation d’énergie, nombreuses stratégies peuvent être adoptées au niveau des systèmes micro-électroniques et des simples dispositifs nano-électroniques. Récemmentle Transistor Tunnel `a effet de champ (Tunnel-FET) s’est imposé comme un candidat possible pour remplacer les dispositifs MOSFET conventionnels pour applications de tr`es basse puissance à des tensions d’alimentation VDD < 0.5V. Nous présentons un modèle Multi-Subband Monte Carlo modifié (MSMC) qui a été adapté pour la simulation de TFET Ultra Thin Body Fully Depleted Seminconductor on Insulator (FDSOIUTB) avec homo- et hétéro-jonctions et des matériaux semi-conducteurs arbitraires. Nous prenons en considération la quantification de la charge avec une correction quantique heuristique mais précise, validée via des modèles quantiques complets et des résultats expérimentaux.Le modèle MSMC a été utilisé pour simuler et évaluer la performance de FD-SOI TFET sidéealisées avec homo- et hétéro-jonction en Si, alliages SiGe ou composés InGaAs. Dans la deuxième partie de l’activité de doctorat un travail de caractérisation à basse températurea été réalisé sur les TFETs en Si et SiGe homo- et hétéro-jonction fabriqués par le centre de recherche français du CEA -LETI. L’objectif est d’estimer la présence de l’effet Tunnel comme principal mécanisme d’injection et la contribution d’autres mécanismes d’injection comme le Trap Assisted Tunneling. / In the last years a significant effort has been spent by the microelectronic industry to reducethe chip power consumption of the electronic systems since the latter is becoming a majorlimitation to CMOS technology scaling.Many strategies can be adopted to reduce the power consumption. They range from thesystem to the electron device level. In the last years Tunnel Field Effect Transistors (TFET)have imposed as possible candidate devices for replacing the convential MOSFET in ultra lowpower application at supply voltages VDD < 0.5V. TFET operation is based on a Band-to-BandTunneling (BtBT) mechanism of carrier injection in the channel and they represent a disruptiverevolutionary device concept.This thesis investigates TFET modeling and simulation, a very challenging topic becauseof the difficulties in modeling BtBT accurately. We present a modified Multi Subband MonteCarlo (MSMC) that has been adapted for the simulation of Planar Ultra Thin Body (UTB)Fully Depleted Semiconductor on Insulator (FD-ScOI) homo- and hetero-junction TFET implementedwith arbitrary semiconductor materials. The model accounts for carrier quantizationwith a heuristic but accurate quantum correction validated by means of comparison with fullquantum model and experimental results.The MSMC model has been used to simulate and assess the performance of idealized homoandhetero-junction TFETs implemented in Si, SiGe alloys or InGaAs compounds.In the second part of the thesis we discuss the characterization of TFETs at low temperature.Si and SiGe homo- and hetero-junction TFETs fabricated by CEA-LETI (Grenoble,France) are considered with the objective to identify the possible presence of alternative injectionmechanisms such as Trap Assisted Tunneling. / Negli ultimi anni uno sforzo significativo `e stato speso dall’industria microelettronica per ridurreil consumo di potenza da parte dei sistemi microelettronici. Esso infatti sta diventando unadelle limitazioni pi`u significative per lo scaling geometrico della tecnologia CMOS.Diverse strategie possono essere adottate per ridurre il consumo di potenza considerando ilsistema microelettronico nella sua totalit`a e scendendo fino a giungere all’ottimizzazione delsingolo dispositivo nano-elettronico. Negli ultimi anni il transistore Tunnel FET (TFET) si`e imposto come un possibile candidato per rimpiazzare, in applicazioni a consumo di potenzaestremamente basso con tensioni di alimentazione inferiori a 0.5V, i transistori convenzionaliMOSFET. Il funzionamento del TFET si basa sul meccanismo di iniezione purament quantisticodel Tunneling da banda a banda (BtBT) e che dovrebbe permettere una significativa riduzionedella potenza dissipata. Il BtBT nei dispositivi convenzionali `e un effetto parassita, nel TFETinvece esso `e utilizzato per poter ottenere significativi miglioramenti delle performance sottosogliae pertanto esso rappresenta una nuova concezione di dispositivo molto innovativa erivoluzionaria.Questa tesi analizza la modellizazione e la simulazione del TFET. Questi sono argomenti moltocomplessi vista la difficolt`a che si hanno nel modellare accuratamente il BtBT. In questo lavoroviene presentata una versione modificata del modello di trasporto Multi Subband Monte Carlo(MSMC) adattato per la simulazione di dispositivi TFET planari Ultra Thin Body Fully DepletedSilicon on Insulator (UTB FD-SOI), implementati con un canale composto da un unicosemiconduttore (omogiunzione) o con differenti materiali semiconduttori (eterogiunzione). Ilmodello proposto tiene il conto l’effetto di quantizzazione dovuto al confinamento dei portatoridi carica, con un’euristico ma accurato sistema di correzione. Tale modello `e stato poivalidato tramite una comparazione con altri modelli completamente quantistici e con risultatisperimentali.Superata la fase di validazione il modello MSMC `e utilizzato per simulare e verificare le performancedi dispositivi TFET implementati come omo o eterogiunzione in Silicio, leghe SiGe,o composti semiconduttori InGaAs.Nella seconda parte della tesi viene illustrato un lavoro di caratterizazione di TFET planari abassa temperatura (fino a 77K). Sono stati misurati dispositivi in Si e SiGe a omo o eterogiuzioneprodotti nella camera bianca del centro di ricerca francese CEA-LETI di Grenoble. Tramite talimisure `e stato possibile identificare la probabile presenza di meccanismi di iniezione alternativial BtBT come il Tunneling assistito da trappole (TAT) dimostrando come questo effetto `e,con ogni probabilit`a, la causa delle scarse performance in sottosoglia dei dispositivi TFETsperimentali a temperatura ambiente.

Molecular-based quantum cellular automata (m-QCA), as an extension of quantum-dot QCAs, offer a novel alternative in which binary information can be encoded in the molecular charge configuration of a cell and propagated via nearest-neighbor Coulombic cell–cell interactions. Appropriate functionality of m-QCAs involves a complex relationship between quantum mechanical effects, such as electron transfer processes within the molecular building blocks, and electrostatic interactions between cells. The influence of structural distortions of single m-QCA are addressed in this paper within a minimal model using an diabatic-to-adiabatic transformation. We show that even small changes of the classical square geometry between driver and target cells, such as those induced by distance variations or shape distortions, can make cells respond to interactions in a far less symmetric fashion, modifying and potentially impairing the expected computational behavior of the m-QCA.