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The geometry of a plasmonic nanostructure determines the charge-current distributions of its localized surface plasmon resonances (LSPR), thereby determining the device’s interactions with external electromagnetic fields. To target specific applications, we manipulate the nanostructure geometry to create different electromagnetic multipole moments, from basic electric and magnetic dipoles to more exotic higher order and toroidal multipoles. The nanoscale nature of the resonance phenomena makes electron beam spectromicroscopy techniques uniquely suited to probe LSPRs over a wide spectral range, with nanoscale spatial resolution. We use electron energy loss spectroscopy (EELS) in a monochromated scanning transmission electron microscope and cathodoluminescence spectroscopy (CL) in a scanning electron microscope to probe the near-field and far-field properties of LSPR. Electric dipoles within triangular prisms and apertures in Sierpiński fractals couple as the generation number is advanced, creating predictable spectral bands from hybridized dipole modes of parent generations with hierarchical patterns of high field intensity, as visualized in EELS. A magnetic dipole moment is engineered using a vertical split ring resonator (VSRR), pushing the limits of nanofabrication techniques. On this nanostructure we demonstrate the calculation of spatially resolved Stokes parameters on the emission of the magnetic dipole mode and a series of coupled rim modes. Coupling of the magnetic dipole mode of four VSRRs in a circular array creates an LSPR mode supporting the lesser-known toroidal dipole moment. We further probe the near-field configuration of this 3D array through tilting under the electron beam in EELS, and the far-field emission through CL of higher order rim modes. We also propose further configurations of five and six VSRRs to strengthen the toroidal dipole moment. All of the data presented herein was analyzed using custom Python code, which provides a unique graphical interface to 3D spectromicroscopy datasets, and a parallelized implementation of the Richardson-Lucy deconvolution algorithm. / Thesis / Doctor of Philosophy (PhD) / Certain types of metallic particles are capable of trapping light on a scale far below that which we can see; their light-trapping properties depend on their material and on their geometry. Using these tiny particles, we can manipulate the behaviour of light with greater freedom than is otherwise possible. In this thesis, we study how we can engineer the geometry of these particles to give predictable responses that can then be targeted towards specific applications. We study a fractal structure with predictable self-similar responses useful for high sensitivity detection of disease or hormone biomarkers; a resonating structure emulating a magnetic response which can be used in the design of unique new materials capable of bending light backwards and cloaking objects from sight; and a combination of these resonators in an array to demonstrate exotic electromagnetic behaviour still on the limit of our understanding.

Les matériaux semi-conducteurs III-N sont à l’origine d’une véritable révolution technologique. Mais malgré l’effervescence autour de ces sources lumineuses, leurs performances dans le vert et l’UV demeurent limitées. La principale raison à cela est l’orientation cristalline (0001)III-N (dite polaire) selon laquelle ces matériaux sont généralement épitaxiés et qui induit de forts effets de polarisation. Ces effets peuvent cependant être fortement atténués par l’utilisation d’orientations de croissance dite semi-polaires. Malheureusement, les films de GaN semi-polaires hétéroépitaxiés présentent des densités de défauts très importantes, ce qui freine très fortement leur utilisation. L’enjeu de cette thèse de doctorat est de réaliser des films de GaN semi-polaire (11-22) de haute qualité cristalline sur un substrat de saphir en utilisant la technique d’épitaxie en phase vapeur aux organométalliques. La réduction de la densité de défaut étant l’objectif majeur, différentes méthodes d’ingénieries de défauts s’appuyant sur la structuration de la surface des substrats et sur la croissance sélective du GaN ont été développées. Elles ont permis d’établir l’état de l’art actuel du GaN semi-polaire hétéroépitaxié. Par la suite, dans le but d’améliorer les performances des DELs vertes, une étude dédiée à l’optimisation de leur zone active a été menée. D’autre part, le développement de substrats autosupportés de GaN semi-polaires, ainsi que la confection de cristaux 3D de grande taille dont la qualité cristalline est comparable aux cristaux de GaN massifs ont été démontrés. Ces deux approches permettant de s’approcher encore plus de la situation idéale que serait l’homoépitaxie. / Nitride based materials are the source of disruptive technologies. Despite the technological turmoil generated by these light sources, their efficiency for green or UV emission is still limited. For these applications, the main issue to address is related to strong polarization effects due to the (0001)III-N crystal growth orientation (polar orientation). Nevertheless these effects can be drastically decreased using semipolar growth orientations. Unfortunately semipolar heteroepitaxial films contain very high defect densities which hamper their adoption for the time being. The aim of this doctoral thesis is to achieve semipolar (11-22) GaN of high quality on sapphire substrate by metalorganic chemical vapor deposition. Defect reduction being the main objective, several defect engineering methods based on sapphire substrate patterning and GaN selective area growth have been developed. Thanks to refined engineering processes, the remaining defect densities have been reduced to a level that establishes the current state of the art in semipolar heteroepitaxial GaN. These results have enabled the achievement of high quality 2 inches semipolar GaN templates, thus forming an ideal platform for the growth of the forthcoming semipolar optoelectronic devices. With this in mind, to improve green LEDs, a study dedicated to the optimization of their active region has been conducted. Finally, the development of semipolar freestanding substrate has been performed, and beyond, the realization of large size crystals with a structural quality similar to that of bulk GaN has been demonstrated. These last two approaches pave the way to quasi-homoepitaxial growth of semipolar structures.

Nitride-based semiconductor materials make it possible to fabricate optoelectronic devices that operate in the whole electromagnetic range, since the band gaps of these compounds can be modified by doping. Among these materials, the sp2-hybridized boron nitride has properties that make it a potential candidate for integration in devices operating in the short-wavelength limit, under harsh environment conditions, due to the strength of the B-N bond.  Nevertheless, this binary compound has been the less studied material among the nitrides, due to the lack of complete control on the growth process. This thesis is focused on the study of the optical properties of sp2-hybridized boron nitride grown by hot-wall chemical vapor deposition (CVD) method, at the Department of Physics, Chemistry and Biology, at Linköping University, Sweden. The samples received for this study were grown on c-plane aluminum nitride as the buffer layer, which in turn was grown by nitridation on c- plane oriented sapphire, as the substrate material. The first objective of the research presented in this thesis was the development of a suitable ellipsometry model in a spectral region ranging from the infrared to the ultraviolet zones of the electromagnetic spectrum, with the aim of obtaining in the process optical properties such as the index of refraction, the energy of the fundamental electronic interband transition, the frequencies for the optical vibrational modes of the crystal lattice, as well as their broadenings, and the numerical values of the dielectric constants; and on the other hand, structural parameters such as the layers thicknesses, and examine the possibility of the presence of roughness or porosity on the boron nitride layer, which may affect the optical properties, by incorporating their effects into the model. The determination of these parameters, and their relation with the growth process, is important for the future adequate design of heterostructure-based devices that incorporate this material. In particular, emphasis has been put on the modeling of the polar lattice resonance contributions, with the TO- LO model, by using infrared spectroscopic ellipsometry as the characterization technique to study the phonon behavior, in the aforementioned spectral region, of the boron nitride. On the other hand, spectroscopic ellipsometry in the visible-ultraviolet spectral range was used to study the behavior of the material, by combining a Cauchy model, including an Urbach tail for the absorption edge, and a Lorentz oscillator in order to account for the absorption in the material in the UV zone. This first step on the research project was carried out at Linköping University.  The second objective in the research project was to carry out additional studies on the samples received, in order to complement the information provided by the ellipsometry model and to improve the model itself, provided that it was possible. The characterization techniques used were X-ray diffraction, which made it possible to confirm that in fact boron nitride was present in the samples studied, and made it possible to verify the crystalline quality of the aforementioned samples, and in turn relate it to the quality of the ellipsometry spectra previously obtained; the Raman spectroscopy made it possible to further verify and compare the crystalline qualities of the samples received, as well as to obtain the frequency for the Raman active B-N stretching vibration in the basal plane, and to compare this value with that corresponding to the bulk sp2-boron nitride; scanning electron microscopy made it possible to observe the rough surface morphologies of the samples and thus relate them to some of the conclusions derived from the ellipsometry model; and finally cathodoluminescence measurements carried out at low temperature (4 K) allowed to obtain a broad band emission, on all the samples studied, which could be related to native defects inside the boron nitride layers, i.e., boron vacancies. Nevertheless, no trace of a free carrier recombination was observed. Considering that the hexagonal-boron nitride is nowadays considered to be a direct band gap semiconductor, it may be indirectly concluded, in principle, that the dominant phase present in the samples studied was the rhombohedral polytype. Moreover, it can be tentatively concluded that the lack of an observable interband recombination may be due to the indirect band gap nature of the rhombohedral phase of the boron nitride. Spectroscopic ellipsometry does not give a definite answer regarding this issue either, because the samples analyzed were crystalline by nature, thus not being possible to use mathematical expressions for the dielectric function models that incorporate the band gap value as a fitting parameter. Therefore, the nature of the band gap emission in the rhombohedral phase of the boron nitride is still an open research question. On the other hand, luminescent emissions originating from radiative excitonic recombinations were not observed in the cathodoluminescence spectra. This second step of the project was carried out at the Leroy Eyring Center for Solid State Science at Arizona State University.

This study investigates the photoluminescence (PL), cathodoluminescence (CL), radioluminescence (RL) and ionoluminescence (IL) of natural and synthetic minerals. The natural minerals (fluorapatite, leucophanite, meliphanite and zircon) are mostly from Ilímaussaq Alkaline Complex in South Greenland, Langesundsfjord in Norway and from different localities within Scotland. Synthetic fluorapatite (manufactured as part of the present study) and zircon doped with rare earth elements (REE) were used to compare single and multidoped materials. This study has shown that many of the generally accepted applications of luminescence are not as straightforward as often suggested by the current literature. For example, the study demonstrates how site distribution of REE, based on luminescence, is greatly affected by the dopant level and structural changes, and that different conclusions can be drawn on the same sample depending on method applied. Furthermore, it is clearly demonstrated that using luminescence as a tool for quantitative trace element determination is not going to be a standard technique in the near future if ever. The two main findings supporting this conclusion are the non-linear intensity decrease between different REE activators in the same sample and a large variation between activators at the concentration at which self-quenching starts. In contrast to the general perception that luminescence related to REE is mostly independent of the host, this study has shown a strong interaction between host and REE activators. This conclusion is supported by the change in the activator’s coordination polyhedron observed with single-crystal and powder X-ray diffraction combined with full chemical characterisation. When combining the weak interaction between some REE with the strong host interaction this study has shown the potential for designing new types of colour tuneable and “white light” LEDs based on natural minerals. This study also reveals that zircon doped with Gd³⁺ and Eu³⁺ can potentially have quantum-cutting properties.

Semiconductor nanowires are nanostructures with lengths up to few microns and small cross sections (10ths of nanometers). In the recent years the development in the field of III-N nanowire technology has been spectacular. In particular they are consider as promising building in nanoscale electronics and optoelectronics devices; such as photodetectors, transistors, biosensors, light source, solar cells, etc. In this work, we present fabrication and the characterization of photodetector and light emitter based devices on III-N nanowires. First we present a study of a visible blind photodetector based on p-i-n GaN nanowires ensembles grown on Si (111). We show that these devices exhibit a high responsivity exceeding that of thin film counterparts. We also demonstrate UV photodetectors based on single nanowires containing GaN/AlN multi-axial quantum discs in the intrinsic region of the nanowires. Photoluminescence and cathodoluminescence spectroscopy show spectral contributions above and below the GaN bandgap according to the variation of the discs thickness. The photocurrent spectra show a sub-band-gap peak related to the interband absorption between the confined states in the large Qdiscs. Finally we present a study of photodetectors and light emitters based on radial InGaN/GaN MQW embedded in GaN wires. The wires used as photodetectors showed a contribution below the GaN bandgap. OBIC measurements demonstrate that, this signal is exclusively generated in the InGaN MQW region. We showed that LEDs based on this structure show a electroluminescence emission and a red shift when the In content present in the QWs increases which is in good agreement with photoluminescence and cathodoluminescence results.

L'étude des propriétés optiques des matériaux semiconducteurs et, notamment, des composés émettant dans l'ultra-violet (UV) constitue depuis quelques années une thématique de recherche de plus en plus importante du fait des applications potentielles de ces matériaux en optoélectronique. Dans cette perspective, étudier les propriétés optiques du nitrure de bore hexagonal (hBN) et des nanotubes de nitrure de bore (BN) est particulièrement intéressant, étant donné leur caractère semiconducteur à grand gap (autour de 6 eV). <br /> L'objectif de cette étude est d'analyser les propriétés optiques de ces matériaux et, plus particulièrement, leurs effets excitoniques, en développant des méthodes de caractérisation optique adaptées pour observer des émissions UV.<br />Les techniques expérimentales de photoluminescence et de cathodoluminescence développées au cours de cette thèse ont tout d'abord permis de comprendre les propriétés de luminescence du hBN. Ainsi, nous avons pu confirmer la présence d'excitons libres émettant à 5.77 eV. Ensuite, en corrélant ces mesures optiques avec des analyses structurales en microscopie électronique en transmission de cristaux individuels, nous avons mis en évidence l'existence d'excitons liés à des défauts structuraux bien déterminés et émettant autour de 5.5 eV. Une fois les propriétés de luminescence du matériau massif connues, nous avons analysé de la même manière différents types de nanotubes de BN multifeuillets. Ces mesures ont pour la première fois montré que ces nano-objets émettent également dans l'UV. En se basant sur notre étude de la luminescence de hBN, nous proposons une interprétation pour l'origine de leurs émissions lumineuses UV.