The quantum confined Stark effect (QCSE) and ultrafast absorption dynamics near the bandedge have been investigated in p-i-n waveguides comprising quantum confined heterostructures grown on GaAs substrates, for emission at 1.3um. The materials are; isolated InAs/InGaAs dot-in-a-well (DWELL) quantum dots (QD), bilayer InAs quantum dots and GaInNAs multiple quantum wells (MQW). The focus was to investigate these dynamics in a planar waveguide geometry, for the purpose of large scale integration in optical systems. Initial measurements of the QCSE using photocurrent measurements showed a small shift for isolated QDs whilst a significant shift of 40nm (at 1340nm) was demonstrated for bilayer dots, comparable to that of GaInNAs MWQ (30nm at 1300nm). These are comparable to InP based quaternary multiple quantum wells used in modulator devices. With the use of a broadband continuum source the isolated quantum dots exhibit both a small QCSE (15nm at 1280nm) and minimal broadening which is desirable for saturable absorbers used in monolithic modelocked semiconductor lasers (MMSL). A robust experimental set-up was developed for characterising waveguide modulators whilst the electroabsorption and electro-refraction was calculated (dn=1.5x10⠻³) using the Kramers-Kronig dispersion relation. Pump probe measurements were performed at room temperature using 250fs pulses from an optical parametric oscillator (OPO) on the three waveguide samples. For the isolated QDs ultrafast absorption recovery was recorded from 62ps (0V) to 700fs (-10V and the shortest times shown to be due to tunneling. Additionally we have shown good agreement of the temperature dependence of these dots and the pulse width durations from a modelocked semiconductor laser using the same material. Bilayer QDs are shown to exhibit ultrafast absorption recovery from 119ps (0V) to 5ps (-10V) offering potential for applications as modelocking elements. The GaInNAs multiple quantum wells show absorption recovery of 55ps (0V), however under applied reverse bias they exhibit long lived field screening transients. These results are explained qualitatively by the spatial separation of electrons and holes at heterobarrier interfaces.

Speeding up addition is the key to faster digital signal processing (DSP). This can be achieved by exploiting the properties of redundant number systems. Their expanded symbol (digit) alphabet gives them multiple representations for most values. Utilising redundant representations at the output of an adder permits addition to be performed without carry-propagation, yielding fast, constant time performance irrespective of the word length. A resource efficient implementation of this fast adder structure is developed that re-purposes the fast carry logic of low-cost field programmable gate arrays (FPGAs). Experiments confirm constant time addition and show that it outperforms binary ripple carry addition at word lengths of greater than 44 bits in a Xilinx Spartan 3 FPGA and 24 bits in an Altera Cyclone III FPGA. Redundancy also provides other properties that can be exploited for performance gain. Some redundant representations will have more zero-symbols than others. These maximise the opportunities to exploit the multiplicative absorbing and additive identity properties of zero that when exercised reduce superfluous calculations. A serial recoding algorithm is developed that generates a redundant representation for a specified value with as few nonzero symbols as possible. Unlike previously published methods, it accepts a wide specification of number systems including those with irregularly spaced symbol alphabets. A Markov analysis and analysis of the elementary cycles in the formulated state machine provides average and worst case measures for the tested number system. Typically, the average number of non-zero symbols is less than a third and the worst case is less than a half. Further to the increase in zero-symbols, zero-dominance is proposed as a new property of redundant number representations. It promotes a set of representations that have uniquely positioned zero-symbols, in a Pareto-optimal sense. This set covers all representations of a value and is used to select representations to optimise the calculation of a dot-product. The dot-product or vector-multiply is a fundamental operation in DSP, since it is employed in filtering, correlation and convolution. The nonzero partial products can be packed together, substantially reducing the calculation time. The application of redundant number systems provides a two-fold benefit. Firstly, the number of nonzero partial products is reduced. Secondly, a novel opportunity is identified to use the representations in the zero-dominant set to optimise the packing further, gaining an extra 18% improvement. An implementation of the proposed dot-product with partial product packing is developed for a Cyclone II FPGA. It outperforms a quad-multiplier binary implementation in throughput by 50% . Redundant number systems excel at increasing performance in particular DSP subsystems, those that are numerically intensive and consist of considerable accumulation. The conversion back to a binary result is the performance bottleneck in the DSP algorithm, taking a time proportional to a binary adder. Therefore, redundant number systems are best utilised when this conversion cost can be amortised over many fast redundant additions, which is typical in many DSP and communications applications.

L’étude de la variation du génotype et du phénotype fut réalisée sur deux espèces de parasites intestinaux (Cryptosporidium parvum et C. muris) via une infection expérimentale de 10 passages successifs chez le veau (Bos taurus). L’infection avec C. parvum a bien fonctionné alors qu’aucun signe clinique n’a été observé dans le cadre de cette étude avec C. muris. Pour le génotype, deux gènes (HSP70 et GP60) ont été amplifiés par double PCR puis séquencés. Les résultats ont indiqué que ces gènes n’étaient pas modifiés après 10 passages chez des veaux. Cela montre une faible évolution génétique du parasite lorsqu’il passe dans un animal hôte, facilitant ainsi les études épidémiologiques lors d’épisode de cryptosporidiose. Il faut cependant noter que les parasites utilisés ne provenaient pas de l’environnement mais d’une compagnie spécialisée en parasitologie (WaterBorne®). L’étude de la variation du phénotype a été tentée, sans succès, à l’aide d’un immuno-buvardage en point utilisant le sérum des veaux infectés. Des problèmes liés à la concentration des ookystes de C. parvum placés sur la membrane de l’immuno-buvardage en point furent suspectés. / The study of the variation of the genotype and phenotype has been done with 2 species of intestinal parasites (Cryptosporidium parvum and C. muris) by using an experimental infection with 10 successives passages on calves (Bos taurus). Infection with C. parvum worked well but failed for C. muris. The genotype has been studied with two genes (HSP70 and GP60), amplified with a double PCR and sequenced. Results showed that these genes are not changing after 10 passages on calves. It indicates that the genetic evolution of the parasite is very slow even when passing to a susceptible host. That particularity might be useful for epidemiologic studies when an episode of cryptosporidiosis occurs. It’s important to consider that the parasites used were not taken from the environment but from a company specialised in parasitology (WaterBorne®). A Dot Blot using serum from infected calves has been tried without success. Problems related to oocysts concentration were suspected.

Colloidal semiconductor quantum dots (QDs) have gained substantial interest as adjustable, bright and spectrally tunable fluorophores in the past decades. Besides their in-depth analyses in the scientific community, first industrial applications as color conversion and color enrichment materials were implemented. However, stability and processability are essential for their successful use in these and further applications. Methods to embed QDs into oxides or polymers can only partially solve this challenge. Recently, our group introduced the embedding of QDs into ionic salts, which holds several advantages in comparison to polymer or oxide-based counterparts. Both gas permeability and environmental-related degradation processes are negligible, making these composites an almost perfect choice of material. To evaluate this new class of QD-salt mixed crystals, a thorough understanding of the formation procedure and the final composites is needed. The present work is focused on embedding both aqueous-based and oil-based metal-chalcogenide QDs into several ionic salts and the investigations of their optical and chemical properties upon incorporation into the mixed crystals. QDs with well-known, reproducible and high-quality synthetic protocols are chosen as emissive species. CdTe QDs were incorporated into NaCl as host matrix by using the straightforward "classical" method. The resulting mixed crystals of various shapes and beautiful colors preserve the strong luminescence of the incorporated QDs. Besides NaCl, also borax and other salts are used as host matrices. Mercaptopropionic acid stabilized CdTe QDs can easily be co-crystallized with NaCl, while thioglycolic acid as stabilizing agent results in only weakly emitting powder-like mixed crystals. This challenge was overcome by adjusting the pH, the amount of free stabilizer and the type of salt used, demonstrating the reproducible incorporation of highest-quality CdTe QDs capped with thioglycolic acid into NaCl and KCl salt crystals. A disadvantage of the "classical" mixed crystallization procedure was its long duration which prevents a straightforward transfer of the protocol to less stable QD colloids, e.g., initially oil-based, ligand exchanged QDs. To address this challenge, the "Liquid-liquid-diffusion-assisted-crystallization" (LLDC) method is introduced. By applying the LLDC, a substantially accelerated ionic crystallization of the QDs is shown, reducing the crystallization time needed by one order of magnitude. This fast process opens the field of incorporating ligand-exchanged Cd-free QDs into NaCl matrices. To overcome the need for a ligand exchange, the LLDC can also be extended towards a two-step approach. In this modified version, the seed-mediated LLDC provides for the first time the ability to incorporate oil-based QDs directly into ionic matrices without a prior phase transfer. The ionic salts appear to be very tight matrices, ensuring the protection of the QDs from the environment. As one of the main results, these matrices provide extraordinary high photo- and chemical stability. It is further demonstrated with absolute measurements of photoluminescence quantum yields (PL-QYs), that the PL-QYs of aqueous CdTe QDs can be considerably increased upon incorporation into a salt matrix by applying the "classical" crystallization procedure. The achievable PL enhancement factors depend strongly on the PL-QYs of the parent QDs and can be described by the change of the dielectric surrounding as well as the passivation of the QD surface. Studies on CdSe/ZnS in NaCl and CdTe in borax showed a crystal-induced PL-QY increase below the values expected for the respective change of the refractive index, supporting the derived hypothesis of surface defect curing by a CdClx formation as one main factor for PL-QY enhancement. The mixed crystals developed in this work show a high suitability as color conversion materials regarding both their stability and spectral tunability. First proof-of-concept devices provide promising results. However, a combination of the highest figures of merit at the same time is intended. This ambitious goal is reached by implementing a model-experimental feedback approach which ensures the desired high optical performance of the used emitters throughout all intermediate steps. Based on the approach, a white LED combining an incandescent-like warm white with an exceptional high color rendering index and a luminous efficacy of radiation is prepared. It is the first time that a combination of this highly related figures of merit could be reached using QD-based color converters. Furthermore, the idea of embedding QDs into ionic matrices gained considerable interest in the scientific community, resulting in various publications of other research groups based on the results presented here. In summary, the present work provides a profound understanding how this new class of QD-salt mixed crystal composites can be efficiently prepared. Applying the different crystallization methods and by changing the matrix material, mixed crystals emitting from blue to the near infrared region of the electromagnetic spectrum can be fabricated using both Cd-containing and Cd-free QDs. The resulting composites show extraordinary optical properties, combining the QDs spectral tunability with the rigid and tight ionic matrix of the salt. Finally, their utilization as a color conversion material resulted in a high-quality white LED that, for the first time, combines an incandescent-like hue with outstanding optical efficacy and color rendering properties. Besides that, the mixed crystals offer huge potential in other high-quality applications which apply photonic and optoelectronic components.

The design, construction and characterisation of a novel, arrayed, open-access optical microcavity is described. Included in this thesis are the precise fabrication details, making use of the focused ion beam. A technique for analysing and optimising the microcavities constructed, making use of an atomic force microscope is also included. Results from the optical characterisation of the fabricated microcavities are presented, including quality factors of around 104, and fitnesses of around 400. The optical analysis then progressed onto coupling colloidal semiconductor nanocrystals to the microcavity modes. This yielded room temperature Purcell enhancements, single particle sensing, and also allowed for the characterisation of a second iteration of cavities. This improved set was shown to achieve fitnesses in excess of 1800 and quality factors with a lower limit of 15000. The optical identification of single NV centres in nanodiamond is discussed, along with the development of an optical apparatus to couple them to microcavities at cryogenic temperatures. Finally several results from finite difference time domain simulations will be presented, showing ultimate mode volumes of less than 0.5 cubic wavelengths are possible for this approach.

Ce mémoire porte sur les mécanismes de relaxation et de fuite des excitons dans des systèmes de boîtes quantiques(BQs) d’InAs/InP. Les systèmes sont composés d’un sub- strat volumique d’InP, appelé matrice (M), d’un puits quantique d’InAs, nommé couche de mouillage (CM), et des familles de BQs d’InAs. La distinction entre les familles est faite par le nombre de monocouche d’épaisseur des boîtes qui sont beaucoup plus larges que hautes. Une revue de littérature retrace les principaux mécanismes de relaxation et de fuite des excitons dans les systèmes. Ensuite, différents modèles portant sur la fuite thermique des excitons des BQs sont comparés. Les types de caractérisations déjà produites et les spécifications des croissances des échantillons sont présentés. L’approche adoptée pour ce mémoire a été de caractériser temporellement la dynamique des BQs avec des mesures d’absorbtion transitoire et de photoluminescence résolue en temps (PLRT) par addition de fréquences. L’expérience d’absorption transitoire n’a pas fait ressortir de résultats très probants, mais elle est expliquée en détails. Les mesures de PLRT ont permis de suivre en température le temps de vie effectif des excitons dans des familles de BQs. Ensuite, avec un modèle de bilan détaillé, qui a été bien explicité, il a été possible d’identifier le rôle de la M et de la CM dans la relaxation et la fuite des excitons dans les BQs. Les ajustements montrent plus précisément que la fuite de porteurs dans les BQs se fait sous la forme de paires d’électrons-trous corrélées. / This thesis focuses on the mechanisms of relaxation and leakage of excitons in systems of quantum dots (QDs) InAs / InP. The systems are composed of a substrate of InP volume, called matrix (M), of a quantum well of InAs, named wetting layer (CM), and of QD families of InAs. The distinction between the families can be explained by the number of monolayer-thick boxes that are wider than high. A literature review highlights the main relaxation mechanisms and leakage of excitons in systems. Then, different models on the thermal leakage of the QD excitons are compared.Then, a presentation of the different types of characterizations already and of the specifications on the samples growths. The approach used for this thesis is to temporarily characterize the dynamic of the QDs with transient absorption and upconversion. The transient absorption experiment’s results are not very convincing, but are minutely explained. PLRT measures were used to follow in temperature the excitons effective lifetime in the QDs families. Then, with a detailed balance model, which has been well explained, it was possible to identify the role of theMand CM in relaxation and leakage of excitons in QDs. As shown by the adjustement, the escape of carriers in the QDs is made in a correlated electron-hole pairs form.

Cette thèse est consacrée à l’étude de deux aspects de la physique mésoscopique que sont le bruit quantique haute fréquence et l'effet de proximité supraconducteur en se focalisant toutefois sur un système modèle: le nanotube de carbone.Ainsi la première partie de cette thèse est dédiée à la mesure de bruit quantique haute fréquence. Afin de mesurer ces fluctuations nous avons développé un système de détection "on-chip" original dans lequel la source de bruit et le détecteur, une jonction Supraconducteur/Isolant/Supraconducteur, sont couplés par un circuit résonant. Cela nous a permis dans un premier temps de mesurer le bruit à l'équilibre du résonateur. Son bruit comporte une forte asymétrie entre émission et absorption reliée aux fluctuations de point zéro. Une seconde étape a été de mesurer le bruit hors équilibre d’émission du passage tunnel de quasi-particules dans une jonction Josephson. Ce bruit comporte une forte dépendance en fréquence en accord avec les prédictions théoriques et nous a permis de valider le principe de détection. Finalement, nous avons pu mesurer le bruit associé au régime Kondo hors équilibre d'une boîte quantique à nanotube de carbone (énergie caractéristique kBTK avec TK la température Kondo). Ce bruit d’émission à kBTK~hν possède une forte singularité à la tension V=hν/e (ν étant la fréquence de mesure). Cette singularité est reliée aux résonances Kondo dans la densité d’états de la boîte associés aux niveaux de Fermi de chaque réservoir. A plus haute fréquence hν~3kBTK, la singularité disparaît, ce qui est compris par des effets de décohérence induits par la tension.Dans la seconde partie, nous avons développé une technique permettant de mesurer à la fois la relation courant/phase et la caractéristique courant/tension d'un lien faible séparant deux supraconducteurs. Nous avons ainsi caractérisé une jonction à base de nanotube de carbone au travers de laquelle une relation courant-phase modulable par une tension de grille a été observée. Cette relation courant/phase exhibe une forte anharmonicité lorsque le supercourant présente une relativement grande amplitude. / This thesis discusses two experiments of mesoscopic physics regarding the high frequency quantum noise and the superconducting proximity effect. We nevertheless focused on a single model system: the carbon nanotube. The first experiment aims to measure the high frequency quantum noise of the tube. In order to measure those fluctuations we have designed an original on-chip detection scheme in which the noise source and the detector, a Superconductor/Insulator/Superconductor junction, were coupled through a resonant circuit. This first allowed us to measure the equilibrium noise of the resonator. It exhibits a strong asymmetry between emission and absorption related to zero point fluctuations. We have then measured the out-of-equilibrium emission noise of quasiparticles tunneling of a Josephson junction. It exhibits a strong frequency dependence in agreement with theoretical predictions and allowed us to validate the detection scheme. Finally, the out-of-equilibrium emission noise associated to the Kondo effect (characteristic energy kBTK with TK the Kondo temperature) in a carbon nanotube quantum dot was measured. We find a strong singularity at voltage V=hν/e (ν is the measurement frequency) for frequency ν~kBTK/h. This singularity is related to resonances in the density of states of the dot pinned at the Fermi energy of the leads. At higher frequency hν~3kBTK the singularity vanishes and understood in terms of decoherence effects induced by the bias voltage. In the second experiment, we have developed a technique allowing to measure in the same experiment the current-phase relation and the current-voltage characteristic of a weak link separating two superconductors. We have characterized a carbon nanotube based junction through which a gate tunable current-phase relation was observed. Jointly to a high critical current amplitude, an anharmonic current-phase relation was measured.

Halbleiter-Quantenpunkte sind Objekte in der Größenordnung von Nanometern, in denen wenige Ladungsträger in alle drei Raumrichtungen durch eine Potentialbarriere eingesperrt sind. Dies führt zu einer reduzierten Wechselwirkung mit dem Halbleiter-Gitter und zu einer diskreten Zustandsdichte. Die große Polarität der Bindung dazu, dass viele Wechselwirkungen direkt durch Spektroskopie der Photolumineszenz zu beobachten sind, was sie für die Grundlagenforschung attraktiv macht. Die ungleiche Anzahl von Elektronen und Löchern erlaubt die Untersuchung einzelner, ungepaarter Ladungsträger. Mit Hilfe der polarisationsaufgelösten Mikro-PL Spektroskopie werden Spinzustände einzelner QP reproduzierbar untersucht. Im Mittelpunkt stehen dabei Wechselwirkungen der Teilchen untereinander. Über die Anregungsspektroskopie werden höherangeregte Zustände identifiziert und charakterisiert. Die hier auftretenden Austauschwechselwirkungen führen zur Mischung zu Feinstrukturen im Spektrum. Kopplungen im angeregten Lochzustand zeigen die Möglichkeit zur optischen Orientierung des residenten Elektrons auf. Die Spinkonfiguration der Elektronen im Triplettzustand erlaubt es, die Elektron-Loch Austauschwechselwirkungen des Trions zu untersuchen. Der zweite Teil dieser Arbeit befasst sich mit semimagnetischen QP. Hier sorgt die Wechselwirkung mit einer paramagnetischen Umgebung von Manganspins für neue magneto-optische Eigenschaften. Diese zeigen sich auf der Ebene einzelner QP in Form von Linienverbreiterungen durch Spinfluktuationen als auch durch den Riesen-Zeeman-Effekt am QP-Ensemble. Besonderes Augenmerk liegt hier auf dem Einfluss der reduzierten Dimensionalität und der größeren Oberflächen der QP auf die Austauschmechanismen. Die starke Temperaturabhängigkeit der Spinumgebung wird ausgenutzt, um das Spinaufheizen als auch die Spin-Gitter-Relaxationsystematisch zu studieren. Dabei wird die PL der QP als Monitor benutzt. / Semiconductor quantum dots are objects on the nanometer scale, where charge carriers are confined in all three dimensions. This leads to a reduced interaction with the semiconductor lattice and to a discrete density of states. In the examined QD in II-VI seminconductor systems the large polar character of the bindings enables to observe particle interactions by spectroscopy of the photo-luminescence, making QD attractive for basic research. An odd number of carriers allows to study the latter in an unpaired state. By using polarization-resolved micro-PL spectroscopy, the spin-states of single, isolated QD can be studied reproducibly. Of special interest are exchange interactions in this few-particle system named trion. By excitation spectroscopy energetically higher states can be identified and characterized. The exchange interactions appearing here lead to state mixing and fine structure patterns in the spectra. Couplings in excited hole states show the way to the optical orientation of the resident electron spin. The spin configuration of the trion triplet state can be used to optically control the resident electron spin. Semimagnetic QD are focused in the second part of this work. The interaction with a paramagnetic environment of manganese spins leads to new magneto-optical properties of the QD. They reveal on a single dot level by line broadening due to spin fluctuations and by the giant Zeeman effect of the dot ensemble. Of special interest in this context is the influence of the reduced system dimension and the relatively larger surface of the system on the exchange mechanisms. The strong temperature dependence of the spin environment is used to systematically study the spin-lattice relaxation. Here, the PL of the QD ensemble monitors the spin temperature. The time constants in the mu range define the range for the incoherent switching of the Mn magnetization.

Les cancers ovariens se distinguent par leur faible incidence, associée à une mortalité élevée, et représente la cinquième cause de mortalité par cancer pour la population féminine. Cette mortalité est due principalement à l’absence de symptômes aux stades précoces des cancers ovariens, retardant leur diagnostic, majoritairement posé lorsqu’une carcinomatose péritonéale est installée. La cavité abdominale est alors envahie par de nombreuses métastases. Le traitement de référence est la chirurgie de cytoréduction complète et la chimiothérapie par voie intraveineuse. Lors de la chirurgie, le chirurgien doit inspecter la totalité de la surface de la cavité péritonéale, et éliminer des tumeurs de toutes tailles, mêmes submillimétriques. Faute de pouvoir détecter toutes les métastases, la cytoréduction est souvent partielle, avec pour conséquence une diminution des chances de guérison. Afin de guider le chirurgien et améliorer le pourcentage de cytoréduction complète, des sondes fluorescentes, conçues pour marquer spécifiquement les tumeurs, ont été développées. Malgré des résultats encourageants, ces sondes souffrent de nombreuses limitations en termes de brillance, de stabilité, et de modularité. Dans ce contexte, de nombreuses nanoparticules, capables de passer outre ces limitations, suscitent un grand intérêt. Parmi celles-ci, des nanocristaux semi-conducteurs, appelés quantum dots, se distinguent par une brillance exceptionnelle. Notre étude s’est basée sur ces quantum dots, associés à un agent de ciblage de référence pour les cancers ovariens, le folate. D’abord testées sur modèles cellulaires et tumoraux in vitro, ces nanoparticules ont démontré de bonnes capacités d’imagerie. Ces propriétés ont ensuite été expérimentées sur modèle murin de carcinomatose péritonéale. Enfin, la bioaccumulation des quantum dots restant un obstacle à leur application clinique, différentes alternatives ont été appliquées pour tenter d’obtenir leur excrétion / Ovarian cancers have a low incidence but a high mortality rate, making them the fifth cause of death by cancer for female population. This high mortality rate is associated with the absence of symptom at the early stage of ovarian cancer, often delaying the diagnosis to advanced stages, mainly peritoneal carcinomatosis. At this stage, metastases have already invaded the abdominal cavity. The reference treatment combines a complete cytoreduction surgery and intravenous chemotherapy. During the cytoreduction, the surgeon must inspect the whole peritoneal surface, and remove all of all sizes, even sub-millimetric. Because of the difficulty to detect and to remove every cancerous tissue, cytoreduction is frequently incomplete, thus reducing the recovery rate. To guide the surgeon and to increase the percentage of complete cytoreduction, fluorescent probes have been developed to target tumors specifically. Despite encouraging results, these probes suffer from many limitations such as low brightness, weak stability and cumbersome modularity. In this context, nanoparticles, that are able to outpass these limitations, have generated a growing interest. Among these nanoparticles, semiconductor nanocristals, called quantum dots, display an exceptional brightness. We investigated these quantum dots, associated with folate, a reference targeting agent for ovarian cancers. Firstly investigated on in vitro cellular and tumor model, folate targeted nanoparticles show encouraging imaging capabilities. These capabilites were also experimented on peritoneal carcinomatosis murine model. Finally, the main obstacle to quantum dot clinical application remains their bioaccumulation, therefore, different alternatives were explored to achieve excretion

O objetivo deste trabalho é examinar os efeitos causados pela interação elétron-fônon em pontos quânticos semicondutores polares. Primeiramente, nós apresentamos cálculos detalhados da taxa de espalhamento e do tempo de relaxação eletrônico em pontos quânticos simples (Single Quantum Dot - SQD) e em dois pontos quânticos acoplados (Coupled Quantum Dots - CQDs) devido à interação entre o elétron e os fônons longitudinais acústicos (LA) na presença e na ausência de campos externos, magnético ou elétrico. O regime de energia usado no cálculo do espalhamento eletrônico foi escolhido de forma que os fônons LA dominam o processo de espalhamento. Nós verificamos que na ausência de campo externo, a taxa de espalhamento do elétron por fônons LA entre dois níveis específicos é essencialmente determinada pela diferença de energia entre estes dois níveis. Observamos que um campo magnético modula fortemente a taxa de espalhamento. Verificamos que o processo de relaxação via multicanais desempenha um papel essencial no mecanismo de relaxação do elétron de estados excitados para o estado fundamental. Um campo magnético externo aumenta ainda mais a relaxação através de transições indiretas. Também fizemos um estudo teórico dos efeitos da interação elétron-fônons longitudinais ópticos (LO) em dois pontos quânticos acoplados compostos de InAs/AlInAs. Fizemos cálculos para o polaron ressonante num regime onde a energia de confinamento do elétron é comparável a energia do fônon L0 utilizando o formalismo da função de Green e teoria de perturbação considerando temperatura zero e finita. Observamos uma renormalização do estado fundamental obtida devido a absorção de fônons virtuais para uma temperatura T > O. Discutimos os efeitos do tunelamento entre os pontos quânticos e a sua influência nas propriedades eletrônicas e analisamos o espectro de absorção óptica neste sistema. Verificamos modificações nos orbitais eletrônicos como resultado direto do tunelamento assistido por fônons. Finalmente, avaliamos os efeitos da interação elétron-fônons L0 na densidade de estados do elétron confinado em pontos quânticos utilizando dois modelos distintos: Um modelo não-perturbativo e o formalismo da função de Green. Estudamos cada método separadamente e avaliamos a densidade de estados como função da temperatura e do confinamento lateral. Consideramos um sistema com apenas dois níveis eletrônicos de energia e comparamos os dois métodos avaliando as suas diferenças básicas. Utilizando o método não-perturbativo fizemos cálculos da densidade de estados para um regime de acoplamento forte entre o elétron e os fônons LO / The purpose of this work is to study effects of electron-phonons interactions in polar semiconductor quantum dots. Firstly, we present a detailed calculation on the electron-LA-phonon scattering rates and electron relaxation processes in single and coupled quantum dots in the absence and in the presence of external magnetic or electric fields. In the absence of external field, interplay among the effective confinement lengths in different directions as well as the phonon wavelength leads to a strong oscillation of the LA-phonon scattering rate between two levels. In other words, the scattering depends strongly on the geometry and confinement potential of the quantum dot. An external magnetic field also strongly modulates the scattering rate in severa1 orders of magnitude. The magnetic field induced effects are very similar in single quantum dot (SQD) and coupled quantum dots (CQDs) where the effective confinement strength in the x-direction affects strongly the scattering rate. However, we find that the multiple relaxation process plays an essential role for electron relaxing from the excited states to ground state both in single and coupled quantum dots. Including all possible relaxation channels, an external magnetic field enhances the relaxation through indirect transitions. Secondly, we present a theoretical study on the effects of electron-LO-phonon interaction in two coupled stacked InAs/InAIAs quantum dots. The contribution of resonant and nonresonant electron-LO-phonon coupling to the polaron states are obtained in the framework of t he Green function formalism and the perturbation approach at zero and finite temperatures. Ground state renormalization is found due to virtual phonon absorption at T > O. Tunneling effects between the dots have been addressed and their influente on the electronic properties and optical absorption are analyzed. Topological modifications of electronic orbitals are found as a result of phonon-assisted tunneling. Finally, we investigate the effects of electron-LO-phonon interaction on the electron density of states in quantum dots using two distinct models. A non-perturbative model and the Green function formalism. Within the non-perturbative model, we consider only two electronic levels in a quantum dot interacting to LO-phonons. An exact solution is obtained for the polaron states and spectral function. We evaluate the density of states in the regime at zero and finite temperature for severa1 values of the lateral confinement. We compare the density of states obtained within the two models. Furthermore, we study the polaron effects in strong electron-LO-phonon coupling regime based on the non-perturbative model