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[en] METHODOLOGIES FOR REPRODUCIBLY TRANSFERRING III-V MATERIALS AND PHOTOVOLTAIC DEVICES TO FLEXIBLE SUBSTRATES / [pt] METODOLOGIAS PARA TRANSFERÊNCIA DE MATERIAIS E DISPOSITIVOS FOTOVOLTAICOS III-V DE FORMA REPRODUTÍVEL PARA SUBSTRATOS FLEXÍVEISMARTIANE DE OLIVEIRA SILVA 24 June 2024 (has links)
[pt] A geração de energia fotovoltaica cresceu rapidamente em todo o mundo e
está começando a contribuir com uma quantidade notável de produção de
eletricidade no cenário mundial. Para desenvolver ainda mais o mercado
fotovoltaico (FV), atrair mais empresas investidoras e torná-lo mais competitivo,
os custos de produção ainda precisam ser reduzidos e a eficiência das células solares
aumentada. Entre todas as tecnologias FV, as células solares de filme fino baseadas
em materiais III-V são a tecnologia de maior sucesso e mais promissora para
alcançar as mais altas eficiências de conversão de energia. Mesmo com a camada
ativa na ordem de micrometros os fotovoltaicos de filmes finos são produzidos
sobre substratos rígidos caros, mas indispensáveis como base cristalográfica e
suporte mecânico na produção da camada ativa monocristalina. Entretanto, após a
obtenção do filme fino FV o substrato original é totalmente dispensável pois não
exerce nenhuma funcionalidade na célula. Desta forma, é crescente o interesse por
tecnologias que permitam a comercialização de células solares sobre substratos
leves, flexíveis e de baixo custo, ampliando não só a gama de aplicabilidades, mas
também diminuindo os custos de produção, transporte e instalação. Este trabalho
mostrará o desenvolvimento de uma metodologia geral para o processo de
transferência de estruturas simples de filmes finos e estruturas de células solares
completas de materiais III-V crescidos epitaxialmente por MOVPE (Metal Organic
Vapour Phase Epitaxy). Materiais III-V foram transferidos para diferentes bases
flexíveis e amostras contendo células solares III-V completas foram transferidas
para substrato flexível de cobre obtido por eletrodeposição e para fita adesiva de
cobre. As transferências foram realizadas com sucesso, sem danificar a estrutura e
os contatos elétricos das células. Medidas de corrente tensão realizadas com
simulador solar Sciencetech SF300A, com filtro AM1.5G, mostraram que as células
em substratos flexíveis quando comparadas com elas em substratos rígidos
apresentaram poucas alterações nas figuras de mérito e eficiência de conversão. As
bases testadas apresentaram aderência, flexibilidade e suporte mecânico esperados
para os filmes finos testados e as células solares completas transferidas. / [en] Photovoltaic power generation has grown rapidly across the world and is
starting to contribute a remarkable amount of electricity production on the world
stage. To further develop the photovoltaic (PV) market, attract more investing
companies and make it more competitive, production costs still need to be reduced
and the efficiency of solar cells increased. Among all PV technologies, thin film
solar cells based on III-V materials are the most successful and most promising
technology to achieve the highest energy conversion efficiencies. Even with the
active layer in the order of micrometers, thin film photovoltaics are produced on
expensive rigid substrates, but indispensable as a crystallographic base and
mechanical support in the production of the monocrystalline active layer. However,
after obtaining the FV thin film, the original substrate is completely unnecessary,
since it does not exert any functionality in the cell. In this way, there is a growing
interest in technologies that allow the commercialization of solar cells on light,
flexible and low-cost substrates, expanding not only the range of applicability, but
also reducing production, transport and installation costs. This work will show the
development of a general methodology for the transfer process of simple thin-film
structures and complete solar cell structures of III-V materials epitaxially grown by
MOVPE (Metal Organic Vapour Phase Epitaxy). III-V materials were transferred
to different flexible bases and samples containing complete III-V solar cells were
transferred to flexible copper substrate obtained by electrodeposition and to copper
adhesive tape. The transfers were carried out successfully, without damaging the
structure or the electrical contacts of the cells. Current voltage measurements,
performed with a Sciencetech SF300A solar simulator, with AM1.5G filter, showed
that cells on the flexible substrates, when compared to them on rigid substrates,
showed little changes in their figures of merit. The bases tested showed adhesion,
flexibility and mechanical support expected for the thin films and complete solar
cells transferred.
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Sources à boîtes quantiques semiconductrices pour la nanophotonique et l'information quantique aux longueurs d'onde des télécommunications / Semiconductor's quantum dot source for the nanophotonic and the quantum information at the telecommunication's wavelengthsElvira Antunez, David 17 September 2012 (has links)
Le siècle dernier a vu l'accomplissement de la mécanique quantique, du traitement de l'information etde l'optique intégrée. Aujourd'hui, ces trois domaines se rencontrent pour donner naissance à l'optiqueintégrée pour les communications quantiques. Un des enjeux aujourd'hui dans ce domaine est ledéveloppement de sources de photons unique aux longueurs d’onde des télécommunications fibrés.Durant ce travail de thèse les émetteurs étudiés sont des boîtes quantiques d’InAsP épitaxiés parEPVOM (Epitaxie en Phase Vapeur aux OrganoMétalliques). On démontrera que ces objets uniquessont capables d’émettre des états quantiques de la lumière grâce à une expérience de dégroupement dephotons. De plus la spectroscopie de ces objets sera déduite des études résolues en temps. Lapossibilité d’intégrer ces objets au sein de nanocavité de taille ultime permet de modifier leur tauxd’émission spontanée, ainsi les résultats obtenus grâce aux cavités métalliques permettent d’observerune accélération de l’émission spontanée sur une large bande spectrale. Finalement il a été mis enévidence une forte modification de l’émission d’un ensemble de boîtes quantiques entre 4K et 300K,en utilisant une technique originale basé sur l’effet laser. / The last century saw the advent of quantum mechanics, information processing and integrated optics.These fields lead to the integrated optics for quantum communication. One of the challenges is thedevelopment of single photon sources operating at fiber’s telecommunication wavelength. In this workwe use quantum dots growth by MOVPE (MetalOrganic Vapour Phase Epitaxy). We demonstratethese emitters can generate some quantum state of light thanks to the antibunching experiment.Moreover the spectroscopy of these objects will be deducted by the time resolved spectroscopy. Thepossibility to integrate these sources in ultimate’s size cavity permits to modify the spontaneous rateemission, so the result obtain with metallic cavity permit to observe an acceleration of the spontaneousemission on a wide spectral band. Finally a strong emission modification of the quantum dot’sensemble between 4K and 300K will be presented by using an original way based on the laser effect.
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Highly coherent III-V-semiconductor laser emitting phase-, amplitude- and polarization-structured light for advanced sensing applications : Vortex, SPIN, Feedback Dynamics / Source laser de haute cohérence, à base semiconducteurs III-V émettant des modes à phase, amplitude et polarisation structurés pour les applications de mesure avancées : vortex, Spin et dynamique de rétro-injection optiqueSeghilani, Mohamed Seghir 07 October 2015 (has links)
Le but de ce travail de thèse est l'étude et la réalisation de sources laser de haute cohérence à semi-conducteurs III-V basées sur la technologie Vertical-External-Cavity-Surface-Emitting-Laser (VeCSEL) à puits quantiques (matériaux InGaAs/GaAs/AlGaAs), émettant dans le proche-IR sur des modes transverses du type Laguerre Gauss (LG) et Hermite Gauss (HG) d'ordre supérieur. Ces modes ont des structures de phase, d'amplitude et de polarisation complexes qui leur vaut souvent l'appellation de 'lumière complexe' ou 'structurée'. Nous mettrons l'accent particulièrement sur les modes LG possédant un moment angulaire orbital, et sur une source contrôlant le spin du photon. Ce type de sources laser présente un grand intérêt pour le développement de systèmes ou capteurs optiques dans différents domaines, tels que les télécommunications, les pinces optiques, et le piégeage et le refroidissement d'atomes, ainsi que la métrologie optique.Nous sommes amenés à étudier les modes propres des cavités optiques de haute finesse. Nous décrivons ces modes suivant les trois "axes" définissant l'état de photon: distributions longitudinal (fréquentiel), transverse (spatial) et de polarisation. Pour chacun de ces trois axes nous étudions les ingrédients physiques qui régissent la formation des modes, et développons les outils théoriques nécessaires à la manipulation et le calcul des états propres dans des cavités modifiées.Dans une seconde étape, puisque la sélection de modes dans une cavité laser passe par l'interaction matière-rayonnement, nous nous penchons sur la dynamique de ces systèmes en écrivant les équations de Maxwell-Bloch pour notre laser. Ces équations nous permettent d'étudier le rôle de la dynamique temporelle dans la sélection des modes lasers et le chemin vers l'état stationnaire. Nous nous appuyons sur ces modèles pour expliquer certaines questions non/mal comprises, et qui mènent parfois à des interprétations erronées dans la littérature scientifique, notamment la sélection spontanée du sens de rotation du front de phase dans les modes vortex.Une partie de ce travail est consacré au développement et la caractérisation d'une technologie à semiconducteurs III-V, qui permet de sélectionner efficacement un mode laser donné, dans la base propre. Nous développons une approche basée sur des méta-matériaux intégrés à la structure de gain (le 1/2-VCSEL) et qui agit comme un masque de phase et d'amplitude. Nous nous appuyons sur cette technologie pour réaliser une cavité laser qui lève la dégénérescence des modes vortex contrarotatif et brise légèrement leur symétrie, ces deux étapes sont cruciales pour pourvoir sélectionner la charge et le signe du vortex généré et stabilisé. Afin de contrôler les modes de polarisation nous étudions les propriétés de polarisation de la cavité et du milieu à gain à puits quantique : la biréfringence, le dichroïsme, et le temps de spin flip dans les puits quantiques. Nous exploitons ces paramètres pour générer les états de polarisation désirés : linéaire stable, circulaire avec un moment angulaire de spin contrôlé par le spin de pompage. À la fin nous présentons la conception et la réalisation d'un capteur laser sous rétro-injection optique (self-mixing) pour la vélocimétrie linéaire et rotationnelle, en utilisant une source laser émettant sur un mode vortex. Ce capteur montre un exemple de mesure inaccessible avec un laser conventionnel. Il tire profit des propriétés uniques des modes vortex pour mesurer simultanément la vitesse linéaire et angulaire des particules. Nous finirons cette partie par l'étude d'un autre design de capteur laser possible pour la granulométrie, utilisant d'autres types de modes laser générés dans ce travail. / The goal of this PhD thesis is the study, design and the development of highly coherent III-V semiconductor laser sources based on multi-quantum wells (InGaAs/GaAs/AlGaAs) Vertical-External-Cavity-Surface-Emitting-Laser (VeCSEL), operating in the near infra-red (IR), and emitting high order Laguerre-Gauss (LG) and Hermite-Gauss (HG) modes. These modes, usually called ‘complex' or ‘structured' light, have a complex wavefronts, amplitudes and polarizations structures. We especially focus on lasers with modes carrying OAM, and also on sources with controlled photon's spin. These modes are of great interest for the development optical systems in several fields, such as telecommunications, optical tweezers, atom trapping and cooling, and sensing applications. We need to study the light eigenstates in high-finesse laser cavities, we describe these eigenstates with respect to the three axis of the light that define the photon state: longitudinal (frequency), transverse (spatial), and polarization. For each one of these axis, we study the physical ingredients governing mode formation, and develop the theoretical tools required for the calculation of the eigenmodes in non-conventional cavities.In a second step, as the mode selection in a laser involves light-matter interaction, we focus on dynamic study by writing the semi classical Maxwell-Bloch equations for our lasers. These equations allow us to study the role of temporal dynamics in laser mode selection, as well as the path the steady state. We use these theoretical models to explain some none /poorly understood questions, and which lead sometimes to erroneous interpretations in the scientific literature. We see in particular the question of the spontaneous selection of the wavefront handedness in vortex modes. We also address the development and the characterization of a III-V semiconductor based technology that enables us to efficiently select the wanted mode in the eigenbasis. We adopt an approach based on metamaterials integrated on the semiconductor gain structure (1/2- VCSEL) that play the role of a phase and amplitude mask. We use this technology to build a laser cavity that lifts the degeneracy and breaks the symmetry between vortex modes with opposite handedness. These two effects are of paramount importance when one wants to select a vortex mode with a well-defined charge and handedness. In order to control the polarization modes, we study the polarization properties of the optical cavity and the quantum-well based gain medium: the birefringence the dichroism, and the spin-flip time in the quantum wells. We make use of these elements to generate the wanted polarization states: stable linear, and circular carrying an angular momentum controlled via the pump spin. In the end, we present the design and building of a feedback laser sensor (self-mixing) for linear and rotational velocimetry, using a laser source emitting a vortex beam. This sensor shows an example of a measurement inaccessible using conventional laser sources. It takes advantage of the orbital angular momentum of the vortex beam to measure both translational and rotational velocities using the Doppler effect. We end this part by presenting other possible sensor designs for particle sizing, using other exotic modes generated in this work.
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Fonctionnalisation de surface de résonateurs plasmoniques à base de semi-conducteur III-V pour la spectroscopie vibrationnelle exaltée / Surface functionalization of plasmonic III-V semiconductors for surface-enhanced vibrational spectroscopyBomers, Mario 13 July 2018 (has links)
Cette thèse traite de la fonctionnalisation de surface des résonateurs plasmonique à base de semi-conducteur III-V en utilisant de l’acide phosphonique pour la spectroscopie vibrationnelle exaltée permettant d'identifier des quantités infimes de molécules. Le premier chapitre décrit les fondements théoriques de la spectroscopie vibrationnelle exaltée. En comparant les propriétés plasmoniques du semi-conducteur dégénéré InAs(Sb):Si et des métaux, ici l’or et le gallium, on trouve que l’InAs(Sb):Si est particulièrement adapté à la spectroscopie infrarouge exaltée (SEIRA) et que le gallium est adapté à la spectroscopie Raman exaltée (SERS). Les deux matériaux plasmoniques alternatifs surpassent théoriquement l'or dans leurs gammes spectrales respectives. Néanmoins, l'or et son inertie chimique restent intéressants pour permettre la spectroscopie vibrationnelle exaltée dans différents environnements chimiques.Dans le deuxième chapitre on démontre que l’InAs(Sb):Si est chimiquement stable dans l'eau, contrairement au GaSb. Une structure en couches composites de GaSb/InAsSb:Si a été utilisée pour montrer que la déplétion de l'antimoine et l'incorporation d'oxygène à l'interface GaSb-eau transforment, en un peu moins de 14 h, 50 nm de GaSb cristallin en un oxyde de gallium. Cet oxyde de gallium a un indice de réfraction moyen-IR de l'ordre de n=1,6 ce qui est environ la moitié de la valeur de l'indice de réfraction du GaSb dans le moyen-IR.Dans le troisième chapitre, on démontre que cette modification de l'indice de réfraction lors de l'oxydation peut être exploitée pour décaler la résonance plasmonique localisée des réseaux InAsSb:Si sur des substrats GaSb dans la plage de 5 µm à 20 µm par formation d’un piédestal.Dans le chapitre 4 est présenté le contrôle de la liaison chimique des molécules organiques avec la fine couche d'oxyde natif à la surface du semi-conducteur III-V. L’attachement de ces molécules sur l’oxyde de surface ouvre la voie à des applications bio-photoniques utilisant des semi-conducteurs améliorés par des résonateurs plasmoniques.Dans le chapitre 5 est décrit deux stratégies différentes pour combiner des résonateurs plasmoniques à base de III-V avec des circuits micro-fluidiques. Ces résultats démontrent que des applications lab-on-the-chip basées sur des semi-conducteurs III-V sont possibles.Enfin, la possibilité d'intégrer des nanoparticules de Gallium plasmoniques sur des semi-conducteurs III-V pour combiner les méthodes SEIRA et SERS est présentée au chapitre 6. / This thesis deals with the surface functionalization of nanostructured plasmonic III-V semiconductors for surface-enhanced vibrational spectroscopy relevant to identify minute amounts of analyte molecules.The first chapter outlines the theoretical foundations of surface-enhanced vibrational spectroscopy based on plasmonics. Comparing the plasmonic properties of the degenerate semiconductor InAs(Sb):Si and of metals, here gold and gallium, it is found that the degenerate semiconductor is especially suited for surface-enhanced infrared (SEIRA) spectroscopy and that gallium with its plasmonic potential in the UV-VIS range is apt for surface-enhanced Raman spectroscopy (SERS). Both alternative plasmonic materials theoretically outperform gold in their respective spectral ranges. Nevertheless, gold and its chemical inertness remain interesting for enabling plasmonic enhanced vibrational spectroscopy in different chemical environments. The influence of aqueous environments on the material properties of III-V semiconductors is addressed in the second and in the third chapter. It is found that InAs(Sb):Si is chemical stable in water, but GaSb is not. A GaSb/InAsSb:Si compound layer structure was used to demonstrate that the depletion of antimony and the incorporation of oxygen at the GaSb-water interface transform 50 nm of crystalline GaSb to a gallium oxide in less than 14 hours. The gallium oxide has a mid-IR refractive index in the order of n=1.6 and thus less than half of the value of the mid-IR refractive index of GaSb. This change in refractive index upon oxidation can be exploited to blue-shift the localized plasmonic resonance of InAsSb:Si gratings on GaSb-substrates in the range from 5 µm to 20 µm by pedestal formation.In Chapter 4, the controlled chemical bonding of organic molecules to the approximately 3 nm thin native oxide layer of III-V semiconductor surfaces by phosphonic acid chemistry is presented. This paves the way for plasmonic enhanced all-semiconductor mid-IR biophotonic applications. In chapter 5, two different, but equally successful strategies to combine III-V based plasmonic resonators with microfluidic circuits are described. These results demonstrate that lab-on-the-chip applications based on III-V semiconductors are possible. Finally, the possibility to integrate plasmonic Gallium nanoparticles onto the III-V material platform for a potential combination of SEIRA and SERS applications is presented in chapter 6.
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Novel Materials, Grid Design Rule, and Characterization Methods for Multi-Junction Solar CellsJanuary 2012 (has links)
abstract: This dissertation addresses challenges pertaining to multi-junction (MJ) solar cells from material development to device design and characterization. Firstly, among the various methods to improve the energy conversion efficiency of MJ solar cells using, a novel approach proposed recently is to use II-VI (MgZnCd)(SeTe) and III-V (AlGaIn)(AsSb) semiconductors lattice-matched on GaSb or InAs substrates for current-matched subcells with minimal defect densities. CdSe/CdTe superlattices are proposed as a potential candidate for a subcell in the MJ solar cell designs using this material system, and therefore the material properties of the superlattices are studied. The high structural qualities of the superlattices are obtained from high resolution X-ray diffraction measurements and cross-sectional transmission electron microscopy images. The effective bandgap energies of the superlattices obtained from the photoluminescence (PL) measurements vary with the layer thicknesses, and are smaller than the bandgap energies of either the constituent material. Furthermore, The PL peak position measured at the steady state exhibits a blue shift that increases with the excess carrier concentration. These results confirm a strong type-II band edge alignment between CdSe and CdTe. The valence band offset between unstrained CdSe and CdTe is determined as 0.63 eV±0.06 eV by fitting the measured PL peak positions using the Kronig-Penney model. The blue shift in PL peak position is found to be primarily caused by the band bending effect based on self-consistent solutions of the Schrödinger and Poisson equations. Secondly, the design of the contact grid layout is studied to maximize the power output and energy conversion efficiency for concentrator solar cells. Because the conventional minimum power loss method used for the contact design is not accurate in determining the series resistance loss, a method of using a distributed series resistance model to maximize the power output is proposed for the contact design. It is found that the junction recombination loss in addition to the series resistance loss and shadowing loss can significantly affect the contact layout. The optimal finger spacing and maximum efficiency calculated by the two methods are close, and the differences are dependent on the series resistance and saturation currents of solar cells. Lastly, the accurate measurements of external quantum efficiency (EQE) are important for the design and development of MJ solar cells. However, the electrical and optical couplings between the subcells have caused EQE measurement artifacts. In order to interpret the measurement artifacts, DC and small signal models are built for the bias condition and the scan of chopped monochromatic light in the EQE measurements. Characterization methods are developed for the device parameters used in the models. The EQE measurement artifacts are found to be caused by the shunt and luminescence coupling effects, and can be minimized using proper voltage and light biases. Novel measurement methods using a pulse voltage bias or a pulse light bias are invented to eliminate the EQE measurement artifacts. These measurement methods are nondestructive and easy to implement. The pulse voltage bias or pulse light bias is superimposed on the conventional DC voltage and light biases, in order to control the operating points of the subcells and counterbalance the effects of shunt and luminescence coupling. The methods are demonstrated for the first time to effectively eliminate the measurement artifacts. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012
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Exploring the Photoresponse and Optical Selection Rules in the Semiconductor Nanowires, Topological Quantum Materials and Ferromagnetic Semiconductor Nanoflakes using Polarized Photocurrent SpectroscopyPournia, Seyyedesadaf 04 October 2021 (has links)
No description available.
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Physics-Based Technology Computer-Aided Design and Compact Modeling with Special Emphasis on Advanced Indium-Phosphide Heterojunction Bipolar TransistorsMüller, Markus 11 July 2024 (has links)
This work investigates the compact- and TCAD modeling of III-V semiconductor based HBTs for high-power and high-speed applications. It demonstrates an approach for modeling such devices that connects compact- and TCAD modeling of such technologies. Compact model extensions are derived based on TCAD simulation. Compact modeling results for two state-of-the-art technologies are presented.:1. Introduction
2. Physical Models for TCAD Simulation
3. Bulk Calibration of Augmented Drift-Diffusion Solver
4. Device Calibration of aDD Solver
5. Application of the GICCR to III-V HBTs
6. Verification of the HICUM/L2 Model Core
7. Model Application to TSC250 InP/InGaAs HBT
8. Model Application to ETH InP/GaAsSb HBT
9. Conclusion and Outlook
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(Al,Ga)(As,P) structures in the GaP matrixDadgostar, Shabnam 15 August 2016 (has links)
GaP ist ein Halbleiter mit einer großen Bandlückenenergie und infolgedessen transparent im größten Teil der sichtbaren Wellenlängen. GaP hat außerdem die kleinste Gitterfehlanpasung zu Si (weniger als 0.4%). Das macht GaP ein interessantes Material für monolithische Integration zu III–V Lichtsender auf Si. Diese Arbeit ist eine Untersuchung über die strukturellen und optische Eigenschaften von (Al, Ga) (As, P) Heterostrukturen auf GaP (001) -Substrat aufgewachsen. Die Einflüsse des PH3 Fluss und Wachstumstemperatur untersucht auf dem Kristallqualität und Oberflächenqualität von AlGaP/GaP Heterostructure. Experimentelle Ergebnisse deuten darauf hin, dass eine Wachstumstemperatur von 490 oC und ein geknackter (engl. cracked) PH3 Fluss von 2.7 sccm zur besten AlGaP Qualität und gleichzeitig zur guten GaP Qualität führen. Um die ineffiziente Lichtemission von GaP zu überwinden wurde GaAs in der GaP-Matrix gewachsen. Die Entstehung der Quantenpunkte wurde durch die 3.7% Gitterfehlanpassung zwischen GaAs und GaP für GaAs Nenndicke über 1,2 ML. Die optischen Messungen zeigen zwei Peaks im Bereich von 1,7 bis 2,1 eV und die Lumineszenz auf Raumtemperatur für 2,7 und 3,6 ML-Proben. Die hohe Energieemission wird der indirekten Rekombination in den dünnen Quantentröge oder kleine gespannte Quantenpunkte zurückzuführen, Während die niedrige Energie Emission ist aufgrund der direkten Elektron-Loch- Rekombination in der entspannten Quantenpunkte. Die Wirkung von Al wird untersucht auf die energetische Bandausrichtung und auf die elektronische Struktur der (Al,Ga)As Quantenstrukturen. Die optische Spektren zeigten einen blaue Verschiebung (engl. blue shift) mit wachsendem Al-Inhalt und die höchste missionsenergie für die (Al,Ga)As/GaP- Heterostruktur war 2.17 eV die zum indirekten Typ-II-Rekombination zusammenhängt. / Transparency of GaP due to the large indirect bandgap energy and its small lattice mismatch with Si make GaP an interesting candidate for optoelectronic devices in visible wavelength. This thesis is an investigation on the structural and optical characteristics of (Al,Ga)(As,P) heterostructures grown on GaP (001) substrates. The influences of the PH3 flux and growth temperature are studied on the crystal and surface quality of AlGaP/GaP heterostructure. The results indicate the narrow growth window of PH3 = 2.7 sccm and growth temperature = 490oC as the optimized conditions. To overcome the inefficient light emission of indirect GaP, direct bandgap GaAs was grown as the quantum structures in the GaP matrix. The QD formation is driven by the 3.7% lattice mismatch between GaAs and GaP for GaAs nominal thickness above 1.2 ML. The optical measurements show two peaks in the range of 1.7 to 2.1 eV and the luminescence up to room temperature for 2.7 and 3.6 ML samples. The high energy emission is attributed to indirect carrier recombination in the thin quantum wells or small strained quantum dots, whereas the low energy red emission is due to the direct electron-hole recombination in the relaxed quantum dots. The influence of the Al content on the band alignment and electronic structure of (Al,Ga)As quantum structures is studied. The optical spectra illustrate the blueshift of the radiative emission with increasing the Al content and the highest emission energy of 2.17 eV is observed for the (Al,Ga)As/GaP system that is related to the indirect type-II radiative recombination.
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Optical properties of InAs/InP nanowire heterostructures / Propriétés optiques des InAs/InP hétérostructures de nanofilsAnufriev, Roman 22 November 2013 (has links)
Ce travail de thèse porte sur l’étude des propriétés optiques de nanofils InP et d’hétérostructures nanofils InAs/InP épitaxiés sur substrat silicium. Ce travail de thèse a été réalisé principalement dans le cadre du projet ANR «INSCOOP». / This thesis is focused upon the experimental investigation of optical properties of InAs/InP NW heterostructures by means of photoluminescence (PL) spectroscopy. First, it was demonstrated that the host-substrate may have significant impacts on the optical properties of pure InP NWs, as due to the strain, created by the difference in the LTECs of the NWs and the host-substrate, as due to some other surface effects. Next, the optical properties of such nanowire heterostructures as quantum rod (QRod) and radial quantum well (QWell) NWs were investigated. The features of obtained spectra were explained using theoretical simulation of similar NW heterostructures. The polarization properties of single InP NWs, InAs/InP QWell-NWs, InAs/InP QRod-NWs and ensemble of the InAs well ordered NWs were studied at different temperatures. Further, we report on the evidences of the strain-induced piezoelectric field in WZ InAs/InP QRod-NWs. Finally, PL QE of NW heterostructures and their planar analogues are measured by means of a PL setup coupled to an integrating sphere. In general, the obtained knowledge of the optical and mechanical properties of pure InP NWs and InAs/InP NW heterostructures will improve understanding of the electrical and mechanical processes taking place in semiconductor NW heterostructures and will serve for the fabrication of future nanodevice applications.
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Nanofils de semiconducteurs III-V épitaxiés sur Si(111) pour la photonique sur silicium / III-V semiconductors nanowires grown by VLS-MBE on Si(111) for silicon photonicsMavel, Amaury 28 February 2017 (has links)
La microélectronique rencontre des difficultés croissantes avec la miniaturisation des composants. La photonique sur silicium propose de les contourner en choisissant le photon comme vecteur de l'information, mais les sources de ces photons restent des verrous. Cette thèse s'est donc attachée à la réalisation par épitaxie par jets moléculaire en mode vapeur-liquide-solide et la caractérisation par spectroscopie de photoluminescence (PL) de boîtes quantiques en nanofils (NFs-BQ) d'InP/InAs crûs sur silicium orienté (111), dans le but d'une intégration monolithique de sources lumineuses. Des NFs d'InP de phase cristalline pure wurtzite ont d'abord été crûs verticaux sur Si(111), à partir d'un catalyseur sous forme de gouttelettes or-indium. La formation préalable d'un piédestal d'InP par la cristallisation de ces gouttelettes, ainsi que la migration de l'or au sommet de ce piédestal pour catalyser la croissance, ont été mise en évidence. Le diamètre de ces NFs a ensuite été augmenté pour qu'ils se comportent comme un matériau massif du point de vue des propriétés optomécaniques. Ils ont été soumis à une pression hydrostatique allant jusqu'à quelques GPa pour déterminer des paramètres mal connus de l'InP Wz. L'optimisation de la croissance du système NF-BQ d'InP/InAs a ensuite été réalisée. Des BQs de hauteur variable ont été obtenues, avec des interfaces très abruptes. Les études de PL sur un ensemble de NFs-BQ montrent des spectres plus ou moins complexes suivant la hauteur des BQs, ainsi qu'une polarisation de l'émission accordable avec cette hauteur. Le dernier objectif a été d'améliorer l'efficacité de l'émission des NFs-BQs d'InP/InAs grâce à l'effet photonique d'une coquille en silicium amorphe (a-Si). Les études de PL ont révélé une forte perte d'intensité de PL et la disparition de l'anisotropie de polarisation de l'émission des NFs-BQ après dépôt. Plusieurs raisons sont discutées pour expliquer ceci. / Microelectronics encounter growing issues with components miniaturization. Silicon photonics offer to avoid them by taking the photon as the information carrier, but the sources are challenging to make. This thesis thus focused on the realization by vapor-liquid-solid assisted molecular beam epitaxy and the characterization by photoluminescence spectroscopy (PL) of InAs/InP quantum dots in nanowires (QD-NW) on (111) oriented silicon, with the aim of monolithic integration of light sources. Pure wurtzite InP NWs have first been vertically grown on Si(111) with a gold-indium droplet catalyst. The preliminary formation of InP pedestals by the crystallization of the droplets, and the migration of gold at the top of the pedestals to catalyze the growth, have been evidenced. The NWs diameter has then been increased so they behave as bulk InP regarding optomechanical properties. The NWs have been put under hydrostatic pressure to several GPa to determine little known InP wurtzite parameters. The growth optimization of the InAs/InP QD-NW system has then been realized. QDs with various height and very sharp interfaces have been obtained. PL studies show more or less complex spectra, according to the QDs' height, as well as a height-tunable polarization. The last goal was to enhance the efficiency of the InAs/InP QD-NWs thanks to the photonic effect brought by an amorphous silicon shell. PL studies revealed a high signal loss and the disappearance of the polarization anisotropy of the QD-NWs emission after deposition. Several hypothesis are discussed.
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