Les antimoniures sont des semi-conducteurs III-V prometteurs pour le développement de dispositifs optoélectroniques puisqu'ils ont une grande mobilité d'électrons, une large gamme spectrale d'émission ou de détection et offrent la possibilité de former des hétérostructures confinées dont la recombinaison est de type I, II ou III. Bien qu'il existe plusieurs publications sur la fabrication de dispositifs utilisant un alliage d'In(x)Ga(1-x)As(y)Sb(1-y) qui émet ou détecte à une certaine longueur d'onde, les détails, à savoir comment sont déterminés les compositions et surtout les alignements de bande, sont rarement explicites. Très peu d'études fondamentales sur l'incorporation d'indium et d'arsenic sous forme de tétramères lors de l'épitaxie par jets moléculaires existent, et les méthodes afin de déterminer l'alignement des bandes des binaires qui composent ces alliages donnent des résultats variables. Un modèle a été construit et a permis de prédire l'alignement des bandes énergétiques des alliages d'In(x)Ga(1-x)As(y)Sb(1-y) avec celles du GaSb pour l'ensemble des compositions possibles. Ce modèle tient compte des effets thermiques, des contraintes élastiques et peut aussi inclure le confinement pour des puits quantiques. De cette manière, il est possible de prédire la transition de type de recombinaison en fonction de la composition. Il est aussi montré que l'indium ségrègue en surface lors de la croissance par épitaxie par jets moléculaires d'In(x)Ga(1-x)Sb sur GaSb, ce qui avait déjà été observé pour ce type de matériau. Il est possible d'éliminer le gradient de composition à cette interface en mouillant la surface d'indium avant la croissance de l'alliage. L'épaisseur d'indium en surface dépend de la température et peut être évaluée par un modèle simple simulant la ségrégation. Dans le cas d'un puits quantique, il y aura une seconde interface GaSb sur In(x)Ga(1-x)Sb où l'indium de surface ira s'incorporer. La croissance de quelques monocouches de GaSb à basse température immédiatement après la croissance de l'alliage permet d'incorporer rapidement ces atomes d'indium et de garder la seconde interface abrupte. Lorsque la composition d'indium ne change plus dans la couche, cette composition correspond au rapport de flux d'atomes d'indium sur celui des éléments III. L'arsenic, dont la source fournit principalement des tétramères, ne s'incorpore pas de la même manière. Les tétramères occupent deux sites en surface et doivent interagir par paire afin de créer des dimères d'arsenic. Ces derniers pourront alors être incorporés dans l'alliage. Un modèle de cinétique de surface a été élaboré afin de rendre compte de la diminution d'incorporation d'arsenic en augmentant le rapport V/III pour une composition nominale d'arsenic fixe dans l'In(x)Ga(1-x)As(y)Sb(1-y). Ce résultat s'explique par le fait que les réactions de deuxième ordre dans la décomposition des tétramères d'arsenic ralentissent considérablement la réaction d'incorporation et permettent à l'antimoine d'occuper majoritairement la surface. Cette observation montre qu'il est préférable d'utiliser une source de dimères d'arsenic, plutôt que de tétramères, afin de mieux contrôler la composition d'arsenic dans la couche. Des puits quantiques d'In(x)Ga(1-x)As(y)Sb(1-y) sur GaSb ont été fabriqués et caractérisés optiquement afin d'observer le passage de recombinaison de type I à type II. Cependant, celui-ci n'a pas pu être observé puisque les spectres étaient dominés par un niveau énergétique dans le GaSb dont la source n'a pu être identifiée. Un problème dans la source de gallium pourrait être à l'origine de ce défaut et la résolution de ce problème est essentielle à la continuité de ces travaux. / Antimonide-based semiconductors are promising in the development of optoelectronic devices considering that the high electron mobility, the possibility to emit or absorb light for a large number of wavelengths in the infrared region and the change in recombination type for confined heterostructure make them a prime subject of research. A good number of publications are aimed at developing devices based on In(x)Ga(1-x)As(y)Sb(1-y) alloys to emit or detect a specific wavelength without giving much information about the composition determination or the band alignment. There are only a few fundamental studies about the incorporation of indium and none about the incorporation of arsenic tetramers by molecular beam epitaxy. Also, the values of the band offsets between binary compounds forming the In(x)Ga(1-x)As(y)Sb(1-y) alloys diverge and the methods used to do so are sometimes arbitrary. A model was constructed and predicts the band alignment between In(x)Ga(1-x)As(y)Sb(1-y) alloys and GaSb for any values of x and y. This model considers thermal effects, strain and confinement for quantum wells. Therefore, it is possible to predict the type of recombination for any composition. Indium atoms tend to segregate on the surface while the growth of In(x)Ga(1-x)Sb on GaSb is taking place by molecular beam epitaxy. This behavior has already been seen before and the work presented here corroborates this observation. It is possible to build up a thin layer of indium on the surface prior to the growth of the alloy to avoid a change of composition in the layer. The thickness of this layer is dependent on the temperature of the substrate and can be evaluated with a simple model of segregation. In the case of a quantum well, there will be another interface where the indium floating on the surface will incorporate. To avoid the formation of a long gradient of composition at this interface, it is recommended to grow a few monolayers of GaSb at low temperature without a growth interruption. This way, the indium will incorporate rapidly and leave a sharp interface. The ratio between the indium beam equivalent pressure and the beam equivalent pressure of indium and gallium gives the nominal composition and is the same as the measured composition by XRD in the alloy. The incorporation of arsenic tetramers is not as straightforward in In(x)Ga(1-x)As(y)Sb(1-y) alloys and is shown to decrease when the V/III ratio is increased as measured by XRD. A simple kinetic model explained that this behavior is caused by antimony occupying a large fraction of the surface. The dissociation of tetramers into dimers is a reaction of second order and the tetramers occupy two sites on the surface and makes the incorporation a slower process. Therefore, the use of arsenic tetramers is not the best choice for a good control on the arsenic composition in the layer. In(x)Ga(1-x)As(y)Sb(1-y) quantum wells were grown on GaSb and were optically characterized to observe the transition of type I recombination to type II. This transition could not be corroborated because all the measurements showed an unknown transition related to the GaSb buffer layer. The origin of this optical signature could not be identified, but may be related to a contaminant in the gallium cell. Identifying the source of this problem and solving it will be essential to go further and observe the transition of type I to type II.

This theoretical thesis presents detailed study of negatively charged excitons - trions - confined in single quantum well in presence of perpendicular magnetic field. Complex valence band of GaAs/GaAlAs compound is described within Luttinger Hamiltonian framework. Singlet and triplet states of negative trion are introduced. Advanced theoretical analysis of Zeeman effect for different states of trion is performed. Landau gauge of magnetic field and unusual wavefunctions basis is chosen and its accuracy is tested. Evolution of ground state energy and photoluminescence spectra with magnetic field is evaluated for different values of Landé g-factors. Probability of occurrence of electrons with respect to the hole position and their spatial correlation function are investigated.

Diese Arbeit präsentiert Untersuchungen zum Wachstum von GaAs Nanodrähten (NWs) und (In,Ga)As Hüllen mittels Molekularstrahlepitaxie (MBE) mit sekundärem Fokus auf den optischen Eigenschaften solcher Kern-Hülle Strukturen. Das ortsselektive Wachstum von GaAs NWs auf mit Oxidmasken beschichteten Si Substraten wird untersucht, wobei der entscheidende Einfluss der Oberflächenpreparation auf die vertikale Ausbeute von NW Feldern aufgedeckt wird. Basierend auf diesen Ergebnissen wird ein zweistufiger Wachstumprozess präsentiert der es ermöglicht NWs mit dünner und gerade Morphologie zu erhalten ohne die vertikale Ausbeute zu verringern. Für die detaillierte Beschreibung der NW Form wird ein Wachstumsmo- dell entwickelt, das die Einflüsse der Veränderung der Tropfen Größe während des Wachstums sowie direktes des Wachstums auf den NW Seitenwänden umfassend beschreibt. Dieses Wachstumsmodell wird benutzt für die Vorhersage der NW Form über einen großen Parameterraum um geeignete Bedingungen für die Realisierung von erwünschten NW Formen und Dimensionen zu finden. Ausgehend von diesen NW Feldern werden die optimalen Parameter für das Wachstum von (In,Ga)As Hüllen untersucht und wir zeigen, dass die Anordnung der Materialquellen im MBE System die Materialqualität entscheidend beeinflusst. Die dreidimensionale Struktur der NWs in Kombination mit der Substratrotation und der Richtungsabhängigkeit der Materialflüsse in MBE resultieren in unterschiedlichen Flusssequenzen auf der NW Seitenfacette welche die Wachstumsdynamik und infolgedessen die Punktde- fektdichte bestimmen. An Proben mit optimaler (In,Ga)As Hülle und äußerer GaAs Hülle zeigen wir, dass thermionische Emission mit anschließender nichtstrahlender Rekombination auf der Oberfläche zu einem starken thermischen Verlöschen der Lumineszenz Intensität führt, welches durch das Hinzufügen einer AlAs Barrierenhülle zur äußeren Hüllenstruktur erfolgreich unterdrückt werden kann. Abschließend wird ein Prozess präsentiert der das ex-situ Tempern von NWs bei hohen Temperaturen ermöglicht, was in der Reduzierung von Inhomogenitäten in den (In,Ga)As Hüllenquantentöpfen führt und in beispiellosen optischen Eigenschaften resultiert. / This thesis presents an investigation of the growth of GaAs nanowires (NWs) and (In,Ga)As shells by molecular beam epitaxy (MBE) with a second focus on the optical properties of these core-shell structures. The selective-area growth of GaAs NWs on Si substrates covered by an oxide mask is investigated, revealing the crucial impact of the surface preparation on the vertical yield of NW arrays. Based on these results, a two-step growth approach is presented that enables the growth of thin and untapered NWs while maintaining the high vertical yield. For a detailed quantitative description of the NW shape evolution, a growth model is derived that comprehensively describes the NW shape resulting from changes of the droplet size during elongation and direct vapour-solid growth on the NW sidewalls. This growth model is used to predict the NW shape over a large parameter space to find suitable conditions for the realization of desired NW shapes and dimensions. Using these GaAs NW arrays as templates, the optimum parameters for the growth of (In,Ga)As shells are investigated and we show that the locations of the sources in the MBE system crucially affect the material quality. Here, the three-dimensional structure of the NWs in combination with the substrate rotation and the directionality of material fluxes in MBE results in different flux sequences on the NW sidefacets that determine the growth dynamics and hence, the point defect density. For GaAs NWs with optimum (In,Ga)As shell and outer GaAs shell, we demonstrate that thermionic emission with successive nonradiative recombination at the surface leads to a strong thermal quenching of the luminescence intensity, which is succesfully suppressed by the addition of an AlAs barrier shell to the outer shell structure. Finally, a process is presented that enables the ex-situ annealing of NWs at high temperatures resulting in the reduction of alloy inhomogeneities in the (In,Ga)As shell quantum wells and small emission linewidths.

Les progrès technologiques dans la fabrication des semi-conducteurs permettent, depuis le début des années 80, de réaliser des dispositifs dans lesquels les électrons sont fortement confinés dans un plan, on parle de système d'électrons bidimensionnels. L'application d'un champ magnétique perpendiculaire intense à ce système permit l'observation des effets Hall quantiques (EHQ), entier en 1980 puis fractionnaire en 1982. En présence du champ magnétique et aux températures extrêmement faibles qui sont concernées, le spectre énergétique des électrons bidimensionnels est quantifié en niveaux de Landau macroscopiquement dégénérés. Le comportement du système est alors déterminé par le facteur de remplissage des niveaux de Landau. L'EHQ entier apparaît autour des valeurs de champ magnétiques qui correspondent à un remplissage entier des niveaux Landau, tandis que son pendant fractionnaire est obtenu autour de certaines fractions du facteur de remplissage ν (ν =1/3, 2/5, 5/2, …) . Alors qu'à remplissage ν entier c'est le comportement individuel des électrons qui gouverne le comportement du système, aux facteurs de remplissage fractionnaires les corrélations électroniques dominent. En raison de ce caractère fortement corrélé, l'EHQ fractionnaire sous-tend un effort de recherche expérimental et théorique important depuis sa découverte. En effet, dans le régime fractionnaire les corrélations fortes induisent des propriétés inédites telles l'existence de quasi-particules de charge fractionnaire, mais elles rendent également la description théorique du système ardue. En 1983, Robert Laughlin proposa une fonction d'onde variationnelle modèle pour la description de l'EHQ fractionnaire observé à remplissage ν=1/3, dont il discuta la validité au regard d'une étude numérique approfondie des interactions entre les électrons. Le succès de cette méthode l'éleva au rang de paradigme, et de nombreuses fonctions d'onde d'essai ont depuis été proposées pour l'explication des effets Hall quantiques observés aux autres facteurs de remplissages. Notamment, la fonction d'onde de Moore et Read s'avère pertinente pour la description de l'EHQ observé à demi-remplissage du second niveau de Landau. Celle-ci suggère l'existence de quasi-particules non-abéliennes qui génère des espoirs importants de par ses applications potentielles en informatique quantique protégée topologiquement. Bien que l'EHQ ait également été observé à demi-remplissage du plus bas niveau de Landau, la nature de l'état sous-jacent est encore débatue. Celui-ci n'est observé que dans les systèmes bicouches et dans les puits larges qui sont au centre de ce travail de thèse. Les puits larges désignent les systèmes dans lesquels l'épaisseur du système d'électrons bidimensionnel ne peut plus être négligée, typiquement à des épaisseurs de l'ordre de 100 nm. En raison du potentiel de confinement ressenti par les électrons, leurs niveaux d'énergies dans la direction du confinement sont quantifiés en sous-bandes. Dans un puits extrêmement fin seule la plus basse sous-bande est peuplée et le degré de liberté correspondant est alors gelé, mais dans les puits large les sous-bandes excitées sont pertinentes. Dans ces conditions l'EHQ fractionnaire à demi-remplissage peut également résulter de la stabilisation d'un état à deux composantes qui peuple les sous-bande excitées. Cet état proposé par Bertrand Halperin en 1983 entre en compétition avec l'état de Moore et Read. En plus de ces deux états, un état métallique de fermions composite est possible, ainsi qu'un cristal électronique de Wigner au comportement isolant. La compétition entre ces différents états est arbitrée par une étude de Monte-Carlo variationnel combinée à des calculs de diagonalisation exacte. La nature de l'état qui est stabilisé dépend de la nature du potentiel de confinement. Dans ce manuscrit de thèse sont discutés les dispositifs de la bicouche, du puits large, ainsi que du puits large en présence d'un biais externe. / Due to technological advances in the manufacture of semiconductors enable, in it possible since the early 80s to create devices in which electrons are strongly confined in a plane, thus effectively realizing a two-dimensional electron system. The application of a strong perpendicular magnetic field to this system led to the observation of the integer quantum Hall effect (QHE) in 1980 and fractional QHE in 1982. Under a strong magnetic field the energy spectrum of the two-dimensional electrons is quantified in Landau levels that are macroscopically degenerate, and the behavior of the system is governed by the filling factor of Landau levels. The integer QHE appears around magnetic field values ​​which correspond to an integer filling of the Landau levels, while the fractional equivalent is obtained around certain fractions of the filling factor ν (ν = 1/3, 2/5, 5 / 2, ...). Although for integers values of ν is the individual behavior of electrons dictates the behavior of the system, the fractional filling factors the electronic correlations dominate. Because of those strong correlations, the underlying fractional QHE motivates an important experimental and theoretical research effort since its discovery. Indeed, in the fractional regime the strong correlations induce novel properties such as the existence fractionally-charged quasiparticles, but they also make the theoretical description of the system laborious. In 1983 Robert Laughlin proposed a variational wave function model for the description of the QHE observed at fractional filling ν = 1/3. He discussed the validity of this trial wave function in a comprehensive numerical study of interactions between electrons. The success of this method made it a paradigm, and many test wave functions have been proposed since then for the explanation of quantum Hall effects observed with other fillings factors. In particular, the wave function of Moore and Read is relevant for the description of the QHE observed at half-filling the second Landau level. This suggests the existence of non-Abelian quasiparticles with potential applications in topologically-protected quantum computing. QHE has also been observed at half filling the lowest Landau level, but the nature of the underlying quantum state is still debated; it is observed that in bilayer systems and wells wide. The large wells, which are the focus of this thesis, refer to systems in which the thickness of the two-dimensional electron system cannot be trivially neglected and usually corresponds to a thickness of about 100 nm. Due to the confinement potential felt by the electrons, their energy levels in the direction of confinement are quantized in sub-bands. In a narrow well only the lowest subband is populated and the corresponding degree of freedom is thus frozen, but in a wide well the excited sub-bands are relevant. Under these conditions fractional QHE at half-filling can also result from the stabilization of a two-state components that also populates the excited sub-band. The corresponding trial state, proposed by Bertrand Halperin in 1983, competes with the state of Moore and Read. In addition to these two states, a metal composite fermion state is a relevant trial state as well as an electronic Wigner crystal, the latter behaving as an insulator. The competition between these states is refered by a variational Monte-Carlo study combined with exact diagonalization calculations. The nature of the state that is stabilized depends on the nature of the confinement potential. In this PhD thesis three confinement potentials are studied: the bilayer, the wide well, and the wide well in the presence of an external bias.

Esta tese compõe-se de contribuições à física das propriedades eletrônicas das heteroestruturas semicondutoras. São investigadas propriedades eletrônicas das duas hetero­estruturas básicas: o poço quântico e a super-rede. Considera-se o poço quântico dopado com impurezas rasas e estudam-se as suas propriedades eletrônicas nos regimes de poço fraca e altamente dopado. No caso de baixa densidade de impurezas é feita uma simulação Monte Carlo. É utilizado um modelo semi-clássico de band de impureza. A interação elétron-elétron é incluída de forma exata e são calculadas as seguintes propriedades do estado fundamental à temperatura zero: densidade de estados de uma partícula, distribuição de carga, energia de Fermi e distribuição do campo elétrico sobre os doadores neutros, todas em função do grau de compensação, da densidade de impurezas e da largura do poço. É observada uma. grande dependência com a compensação. Os resultados são explicados à luz da competição entre os efeitos de desordem e confinamento. É observada a ocorrência de Coulomb Gap característico de sistemas bidimensionais. Mostra-se que a. distribuição de carga possui largura e constante de decaimento determinados independentemente pela compensação e pela concentração de impurezas, respectivamente. Tais resultados são importantes para a caracterização de poços quânticos puros. No limite altamente dopado parte-se de um modelo light-binding desordenado e calcula­se a densidade de estados de uma partícula formada devido ao overlapping entre os estados localizados; utiliza-se o método de Matsubara e Toyosawa. para a obtenção da média sobre configurações. Discutem-se os efeitos da desordem diagonal introduzida pelo potencial de confinamento os quais são comparados com os da. desordem não-diagonal. São apresentados resultados para a densidade de estados em função do grau de confinamento e concentração de impurezas para poços e fios quânticos. Sâo estudadas as propriedades eletrônicas das super-redes sob campo magnético transversal à direção de crescimento. Mostra-se que esta configuração é ideal para o estudo das características básicas das super-redes: a estrutura de mini bandas e o tunelamento. Calculam-se as sub-bandas de condução utilizando a teoria de massa efetiva de muitas bandas. Introduz-se a idéia de massa efetiva renormalizada para barreiras semicondutoras. Comparam-se os resultados com dados experimentais de ressonância ciclotrônica. A ótima concordância obtida demonstra a grande importância e a utilidade do conceito de massa efetiva renormalizada para barreiras semicondutoras, que é uma maneira nova e simples de lidar com as soluções evanescentes. / This thesis is composed of contributions to the theory of electronic properties of semicon­ ductor heterostructures. Electronic properties of the basic two heterostructures (quantum well and superlattice) are investigated. A quantum well doped with shallow impurities is considered and its electronic properties are studied in both limits: lightly and heavily doped. In the first case a Monte Carlo simula­ tion technique is used. A semiclassical impurity band model is used . The electron-electron interaction is included exactly and properties of the ground state such as the density of single particle states, the charge distribution, the Fermi energy and the electric field di tribution on the neutra/ donors are calculated, all of them as a function of the degree of compensation, the impurity concentration and the width of the well. A great dependency with the compensation is observed. The results are explained by the competition between the effects of disorder and confinement. The existence of a Coulomb Gap is verified . The charge distribution is shown to have a width and decay rate given by the degree of compensation and impurity concentration, in this order. Such results are important to characterize pure quantum wells. On the heavily doped limit, a disordered tight-binding model is used and the density of states that is formed by the overlapping of localized states is calculated by using the method of Matsubara and Toyosawa for the configuration average. The diagonal disord er effect introduced by the confinement potential is considered and compared to that of the non­ diagonal disorder. Results of the density of states as a function of the degree of confinement and impurity concentration for quantum wells and wires are presented. The electronic propertie s of a superlattice under a magnetic field which is transversal to the growth direction are studied. Jt is shown that this configuration is id eal for the study of the basic characteristics of the superlattices: the subband structure and the tunneling. The conduction subbands are calculated by using the theory of many bands effective mass. The idea of renormalized effective mass for barriers is introduced. The obtained level spacings are compared with cyclotron resonance experimental data (infrared absorption). The good agreement obtained demonstrates the importance and usefulness of the renormalized effective mass, which is a new and simple way to handle evanescent waves.

Die Dissertation beinhaltet Untersuchungen mittels optischer Rasternahfeldmikroskopie (SNOM)an epitaktisch gewachsenen Halbleiter-Nanostrukturen des Materialsystems GaAs/(Al,Ga)As, sowie Untersuchungen mittels Rasterkraftmikroskopie (AFM/MFM) an ferromagnetischen MnAs-Schichten auf GaAs. Der erste Teil der Arbeit widmet sich dem Aufbau und der Wirkungsweise eines neuen SNOM fürden Einsatz bei tiefen Temperaturen. Das Auflösungsvermögen des Mikroskopswird einmal in Hinblick auf die topographische Empfindlichkeit des Scanners in Richtung der Oberflächennormale, andererseits optisch-lateral charakterisiert. Es wird gezeigt, welche Möglichkeiten der Einsatz geätzter, unbedampfter Nahfeldsonden bietet. Im zweiten Teil werden nahfeld-optische Untersuchungen an GaAs-Quantenfilmen und GaAs-Quantendrähten vorgestellt. Die Grenzflächeneigenschaften der Quantenfilmstrukturen wurden per Wachstumsunterbrechung dahingehend beeinflusst, dass inselartige Gebiete konstanter Quantenfilmdicke entstehen, deren lateraler Durchmesser einige hundert Nanometer beträgt. Durch Photolumineszenzspektroskopie im SNOM kann die räumliche Verteilung der Inseln detektiert werden. Die optischen Nahfeldbilder geben einen interessanten Einblick in die Grenzflächenmorphologie des Quantenfilms und ermöglichen so Rückschlüsse auf die Wachstumsprozesse. Quantendrähte aus GaAs wurden in die intrinsische Zone einer p-i-n-Struktur eingebaut. Durch räumlich aufgelöste sowie energie-selektive Anregung von Photoströmen mittels SNOMkann das Verhalten von zusätzlich in der Struktur erzeugten Ladungsträgern auf den Gesamtstromfluss untersucht werden. Die Ergebnisse liefern ein verbessertes Verständnis über denProzess der selektiven Elektrolumineszenz, durch den diese Strukturen gekennzeichnet sind. Im letzten Teil werden strukturelle Untersuchungen an MnAs-Schichten vorgestellt, die auf GaAs(001) gewachsen wurden. Epitaktisch gewachsene MnAs-Schichten auf GaAs(001) zeigen eine Phasenkoexistenzvon ferromagnetischem und paramagnetischem MnAs unterhalb der Curie-Temperatur. Auf Grund dieser Besonderheit kommt es zur Ausbildung von periodischen elastischen Domänen in der Schicht. Die Entwicklung solcher Domänen wird mittels temperaturabhängiger Rasterkraftmikroskopiedirekt beobachtet. / In this thesis, investigations on both epitactically grown GaAs/(Al,Ga)As semiconductor nanostructures using near-field scanning optical microscopy (SNOM) as well as ferromagnetic MnAs films on GaAs using scanning force microscopy are presented.Setup, operation modes, and properties of a new SNOM designed for low-temperature experiments are discussed. In terms of resolution, both topographical sensitivity of the scanner and optical limitsare distinguished. Surprisingly, the use of uncoated optical fibre tips enables sufficient optical resolution, while the transmission increases dramtically compared to conventional SNOM probes. Using the SNOM setup, near-field optical experiments on GaAs quantum wells and GaAs quantum wiresare made. The interface properties of the quantum well structures had been influenced during growth by interrupting the growth process. Thus, island-like areas with constant well thickness are prepared, whose lateraldiameter is in the order of a few hundred nanometers.Near-field optical photoluminescence spectroscopy can detect the spatial distribution of the islands.The near-field optical images provide interesting insight into the interface morphology and henceabout the growth process itself. GaAs sidewall quantum wires had been grown such that they are built in the center of the intrinsic layer of a p-i-n LED structure.Applying the SNOM, spatially refined photocurrents are induced in the structure. The initial localisation of photogeneratedcharge carriers can also be chosen by varying the excitation energy.This enables a detailed study of how additionally generated carriers contribute to the photocurrent signal,the outcome of which provides deeper understanding in the process of a selective electroluminescenceof the structure. In the last part, structural investigations on MnAs film are discussed, which had been grown on GaAS(001) substrates.These films exhibit a phase coexistense of ferromagnetic and paramagnetic MnAs below the Curie temperature. As a result, periodic elastic domains of the coexisting phases are formed. The development of such domains is studied using temperature-dependent (magnetic) scanning force microscopy.The structural effects are discussed in connection with a theoretical model.

AlGaAs/GaAs- und AlGaAs/GaAs/InGaAs-Quantengraben-Strukturen mit dotiertem Kanal sowie modulationsdotierte AlGaAs/InGaAs/GaAs- Heterostrukturen auf Halbleitermaterialien mit hoher Elektronendriftgeschwindigkeit werden erfolgreich zur Herstellung von Mikro-Hall-Bauelementen eingesetzt. Mit Blick auf ihre Eignung als Magnetfeldsensoren werden die Signal-Linearität, die Sensitivität und das Rauschen bei schwachen und starken elektrischen Feldern untersucht. Auch bei höheren elektrischen Feldern von mehr als 1.8 kV/cm zeigen die Bauelemente mit dotiertem Kanal eine ausgezeichnete Linearität des Signals. Magnetische Empfindlichkeiten von bis zu 600 V/A/T werden im Konstantstrombetrieb gemessen. Unter Verwendung eines Si-δ-dotierten pseudomorphen InGaAs-Quantengrabens wird sowohl eine bessere Sensitivität als auch ein besseres Rauschverhalten erzielt als bei homogen dotiertem GaAs-Kanal. Als beste Signal-Rausch-Empfindlichkeit wird ein Wert von 138 dB/T erreicht für ein Bauelement von 10·10 µm Fläche (bei 300 K, 100 kHz Messfrequenz und 1 Hz Bandbreite). Da das elektrische Verhalten dieser Strukturen besonders durch die hohen Elektronendriftgeschwindigkeiten bestimmt wird, tritt auch bei hohen elektrischen Feldern bis zu 2.4 kV/cm keine Degradation des Bauelementes auf. Als niedrigste Nachweisgrenze für Magnetfelder wird ein Wert von 127 nT/√Hz bestimmt. Verglichen damit, zeigen die modulationsdotierten Bauelemente von 20·20 µm Größe zwar eine höhere Signal-Rausch-Empfindlichkeit von 141 dB/T bei geringen elektrischen Feldern, die sich aber bei höheren Feldstärken stark verschlechtert. Daher haben die Bauelemente mit dotiertem Kanal und pseudomorph verspanntem InGaAs-Quantengraben unter Ausnutzung hoher Elektronendriftgeschwindigkeit bei hohen elektrischen Feldern einige Vorteile gegenüber den modulationsdotierten Strukturen mit hoher Elektronenbeweglichkeit. Untersuchungen der thermischen Stabilität von Bauelementen mit modulationsdotiertem Quantengraben zeigen, dass eine dicke InGaAs-Schicht (innerhalb fixierter Gesamtdicke des GaAs/InGaAs-Kanals) erforderlich ist, um die parasitäre Parallel-Leitfähigkeit des GaAs-Kanals zu vermeiden. Unter Berücksichtigung dieser Erkenntnis und bei Verwendung eines hohen Dotierungsgrades werden ausgezeichnete Temperaturstabilitäten von 90 ppm/K im Konstantstrombetrieb und 192 ppm/K im Konstantspannungsbetrieb erzielt. Unabhängig davon zeigen optische Untersuchungen mit Photolumineszenz-Spektroskopie und Raman-Streuung einen hohen Fehlordnungsgrad in dünnen InGaAs-Quantengräben, der dagegen für dicke pseudomorphe InGaAs-Schichten vernachlässigbar ist. Daher resultiert eine dickere InGaAs-Schicht nicht nur in einer höheren absoluten magnetischen Sensitivität und besseren thermischen Stabilität, sondern auch in geringerem 1/f-Rauschen als Ergebnis von Leitfähigkeitsfluktuationen. Besondere Anstrengungen werden unternommen zum Einsatz der Rauschspektroskopie tiefer Zentren zur Untersuchung der Qualität von Halbleitervolumina bzw. -schichten. In Kombination mit den Untersuchungen der betriebsstromabhängigen Sensitivität erweist sich diese Methode als am Besten geeignet für die Optimierung von Mikro-Hall-Bauelementen. Der Einfluss der Skalierung des Bauelementes auf seine Charakteristika wie Rauschen und magnetische Empfindlichkeit wird untersucht. Sowohl die Signal-Rausch-Empfindlichkeit als auch die Grenzempfindlichkeit sind größenabhängig. Der Einfluss der Geometrie auf die Verteilung des elektrischen Feldes wird für die Form eines Griechischen Kreuzes durch numerische Rechnungen simuliert und diskutiert. Abgerundete Ecken erweisen sich als am Besten geeignet für die Herstellung hochsensitiver und rauscharmer Mikro-Hall-Bauelemente. / Doped-channel quantum well (QW) AlGaAs/GaAs and AlGaAs/GaAs/InGaAs as well as modulation-doped AlGaAs/InGaAs/GaAs heterostructures based on high electron drift velocity semiconductors are successfully applied to the fabrication of micro-Hall devices. Considering these devices as magnetic sensors, their properties were characterized in terms of signal linearity, sensitivity and noise at low and high electric fields. Even at electric fields higher than 1.8 kV/cm, the doped-channel devices exhibit an excellent signal linearity. Magnetic sensitivities up to 600 V/T/A in current drive mode are measured. The usage of a Si-δ-doped pseudomorphic InGaAs QW results in better sensitivity and noise performance than does uniformly doped GaAs. A maximal signal-to-noise sensitivity (SNS) of 138 dB/T is achieved in 10 μm square size device at 300 K, 100 kHz frequency and 1 Hz bandwidth. Because the performance in these structures is driven in part by the high electron drift velocity, it does not degrade even at high electric fields up to 2.4 kV/cm and corresponds to a lowest detection limit of 127 nT/√Hz. Comparatively, the modulation-doped devices of 20 μm square size exhibit a higher SNS of 141 dB/T at low electric fields, but degrade at higher fields. Thus, the doped-channel pseudomorphically strained InGaAs QW high-velocity devices have several advantages over modulation-doped high-mobility structures at high electric fields. Thermal stability studies of doped-channel QW devices reveal a thick InGaAs layer (within a fixed total thickness of the GaAs/InGaAs channel) necessary to avoid the parasitic parallel conductivity in GaAs channel. Using this result and a high doping level, superior temperature stabilities of 90 ppm/K in the current drive mode and 192 ppm/K in the voltage drive mode are attained. Independently, optical studies like photoluminescence and Raman scattering reveal a high degree of disorder in thin InGaAs QWs, being negligible for thick pseudomorphic InGaAs layers. Hence, a thick InGaAs layer causes not only a higher absolute magnetic sensitivity and a better thermal stability, but also lower 1/f noise being a result of conductivity fluctuations. Special effort is devoted to the application of deep level noise spectroscopy as a very sensitive probe for semiconductor bulk and layer quality. Combined with supply-current-related sensitivity studies, this method is most suitable for micro-Hall device optimization. The effect of device scaling on device characteristics like noise and absolute magnetic sensitivity is studied. Both the SNS and detection limit are shown as size-dependent. Additionally, geometry effects on the electric field distribution for Greek cross shapes are simulated by numerical calculations and discussed. Rounded corners appear as most appropriate for the fabrication of highly sensitive low-noise micro-Hall devices.

La photonique du silicium a connu un développent massif pendant les dix derniers années. Presque toutes les briques technologiques de base ont été réalisées et ont démontrées des performances remarquables. Cependant, le manque d’une source laser intégrée en silicium a conduit les chercheurs à développer de composants basés sur l’intégration entre le silicium et les matériaux III-V.Dans cette thèse je décris la conception, la fabrication et la caractérisation des lasers hybrides III-V sur silicium basés sur cette intégration. Je propose un coupleur adiabatique qui permet de transférer intégralement le mode optique du guide silicium au guide III-V. Le guide actif III-V au centre du composant fourni le gain optique et les coupleurs, des deux cotés, assurent le transfert de la lumière dans les guides silicium.Les lasers mono longueur d’onde sont des éléments fondamentaux des communications optiques. Je décris les différentes solutions permettant d’obtenir un laser mono-longueur d’onde hybride III-V sur silicium. Des lasers mono longueur d’onde ont été fabriqués et caractérisés. Ils démontrent un seuil de 21 mA, une puissance de sortie qui dépasse 10 mW et une accordabilité de 45 nm. Ces composants représentent la première démonstration d’un laser accordable hybride III-V sur silicium. / Silicon photonics knew an impressive development in the last ten years. Almost all the fundamental building blocks have been demonstrated and reveal competitive performances. However, the lack of an efficient silicon integrated laser source has led the researchers to develop heterogeneous integration of III-V materials on silicon.In this thesis I describe the design, the fabrication and the performances of these hybrid III-V on silicon lasers. I propose the use of an adiabatic coupler that totally transfers the optical mode between the III-V and the silicon waveguides. The active waveguide on III-V materials at the center of the device provides the optical gain, while, on both side, adiabatic couplers allow a loss-less transfer of the optical mode to the silicon waveguide. Single wavelength emitting lasers are fundamental elements for high bandwidth optical links. I review all the effective solutions enabling single waveguide hybrid III-V on SOI lasers. DBR, microring based, DFB and AWG laser solutions were analysed. Single wavelength operating lasers have been fabricated and characterized. A laser threshold of only 21 mA, an output power of more than 10 mW and tunability over 45 nm with a SMSR of 45 dB have been measured. These devices represent the first demonstration of a monolithically integrated hybrid III-V/Si tunable laser made by wafer bonding technique.

Nós calculamos o efeito da interação elétron-fonons longitudinais óticos (LO) sobre a energia de transição ls &#8594 2p+ entre os níveis de uma impureza doadora, localizada em um poço quântico de GaAs-AlxGa1-xAs. Nossos resultados para a energia de transição em função do campo magnético aplicado mostram claramente, que a saturação da energia de transição (efeito pinning) ocorre na energia dos fônons LO, em boa concordância com recentes dados experimentais. Obtemos também a massa de cíclotron de polarons confinados em fios quânticos quase-unidimensionais, com potencial de confinamento parabólico. Observamos que o comportamento da massa é diferente daquele para sistemas bi-dimensionais e que esta diferença é maior quanto maior o potencial de confinamento. Para a heterojunção de GaAs-AlGaAs e GaAs-GaSb, investigamos a importância da interação elétron-fonons interfaciais sobre a massa de cíclotron. Verificamos que a contribuição dos fonons interfaciais é fundamental nas regiões próximas às resonâncias, onde domina o espectro. Finalmente, calculamos a energia de ligação de uma impureza hidrogenóide, localizada no centro de um ponto quântico circular de GaAs-AlGaAs. Na ausência de campo magnético aplicado, obtivemos uma expressão analítica para a função de onda do elétron ligado. Notamos, que a influência do campo magnético sobre a energia de ligação é fraca nas regiões de pequenos raios, devido ao forte potencial de confinamento. / We calculate the effects of the electron-longitudinal optical (LO) phonons interaction on the intra donor ls &#8594 2p+ transition energy in GaAs-AlGaAs quantum wells structures. Our results to the transition energy as a function of the magnetic Field strength, show that the pinning effect occur in the phonon LO energy in good agreement with recent experimental data. The cyclotron mass of polarons confined in quasi.one.dimensional quantum-well wires with parabolic confinement potential, is also obtained. The behavior of electrons effective mass with magnetic field is different, of the two-dimensional systems, and the difference increase when the confinement potential increase. To heterojunctions of GaAs-AlAs and GaAs-GaSb, we investigate the electroninterfacials optical (IO) phonons interactions on the effective cyclotron mass. We find that the electron-IO-phonons interaction is fundamental near the resonances, where they dominate the spectra. Finally, the ground state binding energy of donor impurity, placed in the center of a circular quantum dot is calculated. Without magnetic field, we obtained the analytic expression to the bound electron wave function. The influence of the magnetic field on the donor binding energy is weaker, when the radius of the quantum dot became smaller.

Previous research in InGaN/GaN light emitting diodes (LEDs) employing semi-classical drift-diffusion models has used reduced polarization constants without much physical explanantion. This paper investigates possible physical explanations for this effective polarization reduction in InGaN LEDs through the use of the simulation software SiLENSe. One major problem of current LED simulations is the assumption of perfectly discrete transitions between the quantum well (QW) and blocking layers when experiments have shown this to not be the case. The In concentration profile within InGaN multiple quantum well (MQW) devices shows much smoother and delayed transitions indicative of indium diffusion and drift during common atomic deposition techniques (e.g. molecular beam epitaxy, chemical vapor deposition). In this case the InGaN square QW approximation may not be valid in modeling the devices' true electronic behavior. A simulation of a 3QW InGaN/GaN LED heterostructure with an AlGaN electron blocking layer is discussed in this paper. Polarization coefficients were reduced to 70% and 40% empirical values to simulate polarization shielding effects. QW shapes of square (3 nm), trapezoidal, and triangular profiles were used to simulate realistic QW shapes. The J-V characteristic and electron-hole wavefunctions of each device were monitored. Polarization reduction decreased the onset voltage from 4.0 V to 3.0 V while QW size reduction decreased the onset voltage from 4.0 V to 3.5 V. The increased current density in both cases can be attributed to increased wavefunction overlap in the QWs.