Heterostructures of materials with dramatically different properties are exciting for a variety of devices. In particular, the epitaxial integration of metals with semiconductors is promising for low-loss tunnel junctions, embedded Ohmic contacts, high-conductivity spreading layers, as well as optical devices based on the surface plasmons at metal/semiconductor interfaces. This thesis investigates the structural, electrical, and optical properties of compound (III-V) semiconductors employing rare-earth monopnictide (RE-V) nanostructures. Tunnel junctions employing RE-V nanoparticles are developed to enhance current optical devices, and the epitaxial incorporation of RE-V films is discussed for embedded electrical and plasmonic devices. Leveraging the favorable band alignments of RE-V materials in GaAs and GaSb semiconductors, nanoparticle-enhanced tunnel junctions are investigated for applications of wide-bandgap tunnel junctions and lightly-doped tunnel junctions in optical devices. Through optimization of the growth space, ErAs nanoparticle-enhanced GaAs tunnel junctions exhibit conductivity similar to the best reports on the material system. Additionally, GaSb-based tunnel junctions are developed with low p-type doping that could reduce optical loss in the cladding of a 4 μm laser by ~75%. These tunnel junctions have several advantages over competing approaches, including improved thermal stability, precise control over nanoparticle location, and incorporation of a manifold of states at the tunnel junction interface. Investigating the integration of RE-V nanostructures into optical devices revealed important details of the RE-V growth, allowing for quantum wells to be grown within 15nm of an ErAs nanoparticle layer with minimal degradation (i.e. 95% of the peak photoluminescence intensity). This investigation into the MBE growth of ErAs provides the foundation for enhancing optical devices with RE-V nanostructures. Additionally, the improved understanding of ErAs growth leads to development of a method to grow full films of RE-V embedded in III-V materials. The growth method overcomes the mismatch in rotational symmetry of RE-V and III-V materials by seeding film growth with epitaxial nanoparticles, and growing the film through a thin III-V spacer. The growth of RE-V films is promising for both embedded electrical devices as well as a potential path towards realization of plasmonic devices with epitaxially integrated metallic films. / text

A wide range of applications have been recognized for terahertz radiations. In fact, medical imaging, homeland security screening, very high-speed wireless telecommunications systems and even drug and gas detection are boosting the development of terahertz emitters and receivers. The work of this thesis is among the efforts in that regard. Actual terahertz detectors are suffering many drawbacks, they are bulky, very slow, not very sensitive or operates at non-practical temperatures. Combined with the complexity to realize terahertz emitters, it explains the difficulties of terahertz radiations to ensure market penetration with practicable civil applications. In that regard, we aim to better understand and improve a specific terahertz photodetector: the Terahertz Quantum Well Photodetector. Those devices working principle relies on a photocurrent created by the excitation of electrons from ground states of quantum wells to the continuum under terahertz impinging light. The intensity of the photocurrent is depending on the intensity of the radiation received by the device. The device active region is made of a multiple quantum wells GaAs/AlGaAs system. By changing the design of the device, that is the thicknesses of each layer, the aluminum fraction of the doping concentration, we can modify its performances. Documented and commented Matlab functions and routines have been implemented in order to simulate a given structure and scripts have been written to find the optimum parameters for a target absorption frequency. Our model has been verified by comparison with experimental data reported in the literature. Based on our model, we systematically study the impact of the active region and contact parameters on the device performances. In addition, innovative designs are proposed in order to reduce the undesirable dark current and thus increase the detectivity. They benefits from many-body effects, effects that are usually a constraint on the design. To our knowledge this is the first time those effects are used to realize innovative designs and increase the performances of quantum well infrared photodetectors. Finally we expose other designs that have been tested in the infrared domain with QWIP and adapt them to the terahertz range. In particular, we propose a quantum cascade photodetector, a double barrier bound-to-miniband and a phonon-assisted band to miniband structures.

Spectrally-resolved differential reflectivity experiments on GaMnAs over a broad spectral range (1.4-2.0 eV) are presented, representing the first such measurements in a III-Mn-V diluted magnetic semiconductor. Comparison of the measured nonlinear spectra with results in GaAs and LT-GaAs, together with calculations of the pump probe signal contributions, has allowed an unambiguous identification of the relevant scattering and relaxation processes for optically-excited carriers in this material system. The measured spectra indicate a clear blue shift in the nonlinear optical response, providing support for the valence band model of ferromagnetism in III-Mn-V diluted magnetic semiconductors. / Spectrally-resolved differential reflectivity experiments on GaMnAs over a broad spectral range (1.4-2.0 eV) are presented, representing the first such measurements in a III-Mn-V diluted magnetic semiconductor. Comparison of the measured nonlinear spectra with results in GaAs and LT-GaAs, together with calculations of the pump probe signal contributions, has allowed an unambiguous identification of the relevant scattering and relaxation processes for optically-excited carriers in this material system. The measured spectra indicate a clear blue shift in the nonlinear optical response, providing support for the valence band model of ferromagnetism in III-Mn-V diluted magnetic semiconductors.

The main objective of this research is to fabricate and characterize an optically integrated interferometric sensor on standard silicon and silicon CMOS circuitry. An optical sensor system of this nature would provide the high sensitivity and immunity to electromagnetic interference found in interferometric based sensors in a lightweight, compact package capable of being deployed in a multitude of situations inappropriate for standard sensor configurations. There are several challenges involved in implementing this system. These include the development of a suitable optical emitter for the sensor system, the interface between the various optically embedded components, and the compatibility of the Si CMOS with heterogeneous integration techniques. The research reported outlines a process for integrating an integrated sensor on Si CMOS circuitry using CMOS compatible materials, integration techniques, and emitter components.

Pour certaines applications, les lasers offrent un choix trop restreint de longueurs d'ondes, et une faible accordabilité. Ces limitations viennent du fait que l'effet laser utilise des résonances atomiques. L'optique non-linéaire permet de s'en affranchir c'est un phénomène non résonnant, donc peu sélectif en longueur d'onde. Néanmoins elle présente des caractéristiques particulières : trois fréquences différentes mises en jeu, l'absence de stockage d'énergie, et le rôle primordial de la phase relative entre les ondes. Dans ce travail nous mettons à profit ces specificités pour mettre en forme spectralement ou temporellement l'émission de lumière dans des sources infrarouges. La première source réalisée est un oscillateur paramétrique optique (OPO) à 3 μm utilisa! nt deux cristaux de KTA. Ses performances sont discutées en régime nanoseconde. Puis nous réalisons un OPO à cristal de PPLN générant des impulsions courtes sous pompage continu par modulation active des pertes. Nous proposons ensuite d'utiliser un absorbant saturable pour verrouiller passivement les modes d'un OPO continu présentant un fort désaccord de vitesse de groupe entre la pompe et le signal. Enfin, nous considérons le cas des sources intégrant à la fois un milieu laser et un dispositif non-linéaire. Nous présentons d'abord un miroir non-linéaire à base de PPLN intégré dans un laser Cr:ZnSe, permettant de produire des impulsions picosecondes accordables autour de 2,5 μm. Nous proposons ensuite de généraliser ce principe en intégrant un OPO dans un laser afin de réaliser une source ultrabrève compacte et accordable.

Ultra-broadband Monolithic Microwave Integrated Circuit (MMIC) amplifiers find applications in multi-gigabit communication systems for 5G and millimeter wave measurement instrumentation systems. The aim of the research was to achieve maximum bandwidth of operation of the amplifier from the foundry process used and high reverse isolation ( < -25.0 dB) across the whole bandwidth. To achieve this, several design variations of DC - 110 GHzMMIC Cascode TravellingWave Amplifier (TWA) on 100 nm AlGaAs/GaAs pHEMT process were done for application in next generation instrumentation and high data transfer rate (100 Gb/s) optical modulator systems. The foundry service and device models used for the design are of the WINPP10-10 process from WIN Semiconductor Corp., Taiwan, a commercial and highly stable process. The cut-off frequency ft and maximum frequency of oscillation fmax for this process are 135 GHz and 185 GHz respectively. Thus, the design was aimed at pushing the ultimate limits of operation for this process. The design specifications were targeted to have S21 = 9.0 to 10.0 ± 1.0 dB, S11 & S22 ≤ -10.0 dB and S12 ≤ -25.0 dB in the whole frequency range. In order to achieve the targeted RF performance, it is imperative to have accurate transistor models over the frequency range of operation, transistor configuration mode and operating bias points. Using smaller periphery transistors results in lower extrinsic & intrinsic input and output capacitances that lead to achieving very wide band performance. Thus, device sizes as small as 2x10 μm were used for the design. A cascode topology, which is a series connection of a common-source and common-gate field effect transistor (FET), was used to achieve large bandwidth of operation, high reverse isolation and high input and output impedance. Using very small periphery devices at cascode bias points posed limitation in the design in terms of accuracy of transistor models under these conditions, specifically at high frequencies i.e., above 50 GHz. One of the major systemrequirements for the application of MMIC ultra-broadband amplifiers in instrumentation is to achieve and maintain high reverse isolation (≤ -25.0 dB) over the whole frequency range of operation which cannot be achieved alone by the cascode topology and new design techniques have to be devised. These twomajor challenges, namely high frequency small periphery FET model modification & development and design technique to achieve high reverse isolation in ultra-broadband frequency range have been addressed in this research.

abstract: GaAs-based solar cells have attracted much interest because of their high conversion efficiencies of ~28% under one sun illumination. The main carrier recombination mechanisms in the GaAs-based solar cells are surface recombination, radiative recombination and non-radiative recombination. Photon recycling reduces the effect of radiative recombination and is an approach to obtain the device performance described by detailed balance theory. The photon recycling model has been developed and was applied to investigate the loss mechanisms in the state-of-the-art GaAs-based solar cell structures using PC1D software. A standard fabrication process of the GaAs-based solar cells is as follows: wafer preparation, individual cell isolation by mesa, n- and p-type metallization, rapid thermal annealing (RTA), cap layer etching, and anti-reflection coating (ARC). The growth rate for GaAs-based materials is one of critical factors to determine the cost for the growth of GaAs-based solar cells. The cost for fabricating GaAs-based solar cells can be reduced if the growth rate is increased without degrading the crystalline quality. The solar cell wafers grown at different growth rates of 14 &mu;m/hour and 55 &mu;m/hour were discussed in this work. The structural properties of the wafers were characterized by X-ray diffraction (XRD) to identify the crystalline quality, and then the as-grown wafers were fabricated into solar cell devices under the same process conditions. The optical and electrical properties such as surface reflection, external quantum efficiency (EQE), dark I-V, Suns-Voc, and illuminated I-V under one sun using a solar simulator were measured to compare the performances of the solar cells with different growth rates. Some simulations in PC1D have been demonstrated to investigate the reasons of the different device performances between fast growth and slow growth structures. A further analysis of the minority carrier lifetime is needed to investigate into the difference in device performances. / Dissertation/Thesis / M.S. Electrical Engineering 2014

Les excitons spatialement indirects, en tant que bosons composites, sont des candidats prometteurs pour l'exploration des systèmes corrélés à N-corps. Ils possèdent une dipôle électrique intrinsèque et une variété de spin 4 fois dégénérée, et devraient former un condensat de Bose-Einstein au-dessous de quelques Kelvins. De récents résultats théoriques montrent que cette condensation doit se produire au sein des états optiquement noirs. Néanmoins les interactions peuvent créer un couplage cohérent vers une population brillante, rendant ainsi accessible la détection du condensat par le biais de sa photoluminescence. Nos expériences portent sur un gaz froid d'excitons indirects dans un double puits quantique. Les excitons sont photo-générés par une excitation laser et confinés dans un piège électrostatique. Nous avons observé une réduction de la population d'excitons brillants pour un gaz de densité fixe à basses températures. Ceci contraste fortement avec le comportement attendu d'un gaz froid soumis à la statistique de Maxwell-Boltzmann. Ces résultats expérimentaux sont confirmés par un modèle phénoménologique montrant que la condensation dans les états noirs est compatible avec le noircissement anormal observé. Une réduction de la température pourrait en principe amplifier ces signatures, cependant dans le GaAs l'interaction exciton-phonon permettant le refroidissement est fortement réduite pour des températures inférieures au Kelvin. Nous avons donc développé une technique permettant le contrôle in-situ du confinement des excitons indirects sans échauffement du gaz, ouvrant ainsi la voie à l'exploration du refroidissement évaporatif des excitons. / Spatially indirect excitons, being composite bosons, are attractive candidates to explore correlated many-body systems. They possess an inherent electric dipole and a four-fold spin manifold. Indirect excitons are expected to form a BEC below a few Kelvins. Recent theoretical results show this condensation must occur in optically dark states. Interactions, however, can lead to a coherent coupling to a bright population, rendering the condensate accessible through its PL. Here we report on a cold gas of indirect excitons in coupled quantum wells. indirect excitons are photo-generated through pulsed laser excitation. Indirect excitons are confined in an electrostatic traps. Thus, we are able to observe an anomaluos depletion of the bright state population for a fixed gas density at lower bath temperatures. This stands in stark contrast to the expected classical behavior of a cold gas of indirect excitons obeying Maxwell-Boltzmann statistics. The experimental results are confirmed by a phenomenological model showing that condensation into the dark state is compatible with the observed anomalous darkening. Reducing the gas temperature should reinforce these signatures. However, in GaAs exciton-phonon interaction is strongly reduced for sub-Kelvin temperatures. We have thus developed a technique to control the indirect excitons confinement in-situ. Our method does not increase the gas temperature and thus paves the way towards the exploration of evaporative cooling for indirect excitons.

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