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Organische, lichtemittierende Dioden (OLEDs) bezeichnen neuartige Lichtquellen, welche zur Beleuchtung oder für Displayanwendungen nutzbar sind. Im Allgemeinen ist die Lichtausbeute durch den hohen Brechungsindex und die Dünnschichtgeometrie der OLED begrenzt. Der hohe Brechungsindex sorgt dafür, dass ein signifikanter Anteil des emittierten Lichts in der OLED durch Totalreflexion (TIR) gefangen ist. Durch den Dünnschichtaufbau der OLED wird außerdem die Lichterzeugung für resonante Moden der kohärenten optischen Mikrokavität erhöht. Dies gilt im Besonderen für die nichtstrahlenden Moden. In dieser Arbeit wurden zwei Methoden untersucht, um die Lichtausbeute aus OLEDs zu erhöhen. Zuerst wurde die Implementierung von Materialien mit niedrigem Brechungsindex angrenzend zum undurchsichtigen metallischen Rückkontakt untersucht. Die Modifizierung des Brechungindexes verändert die Dispersionsrelation der an der Grenzfläche zwischen Metall und Dielektrikum angeregten nicht-strahlenden Oberflächenplasmonpolariton-Resonanz (SPP). Dadurch wird der Phasenraum verkleinert, in welchen effizient Strahlung abgegeben werden kann. Da die SPP-Resonanz eine nichtstrahlende Verlustquelle der Mikrokavität darstellt, wird so die Auskopplungseffizienz der OLED erhöht. In experimentellen Umsetzungen konnte die externe Quanteneffizienz (EQE) sowohl für einen Emitter gesteigert werden, welcher eine isotrope Verteilung der Strahlungsquellen besitzt (Ir(ppy)3 , +19 %), als auch für eine vorzugsweise horizontale Ausrichtung (Ir(ppy)2 (acac), +18 %). Die Steigerung der EQE korrespondiert sehr gut mit der berechneten Steigerung der Auskopplungseffizienz für die jeweiligen Mikrokavitäten (+23 %, bzw. +19 %). Weitere optische Simulationen legen den Schluss nahe, dass dieser Ansatz ebenso für perfekt horizontale Ausrichtung der Quellen sowie für weiße OLEDs anwendbar ist. Als zweiter Ansatz wurde die erhöhte Lichtausbeute durch Bragg-Streuung an periodische Linienstrukturen untersucht. In dieser Arbeit wurden Methoden untersucht, bei denen die Oberflächen strukturiert wurde, auf welche die organischen Halbleiterschichten der OLEDs aufgebracht wurden. Für bottom-OLEDs (durch ein Substrat emittierende OLEDs), wurde direkt die transparente Elektrode durch ein Laserinterferenzablationsverfahren (DLIP) modifiziert. Zusätzlich wurden top-OLEDs untersucht (direkt aus der Mikrokavität Licht emittierende OLEDs), für welche alle Schichten auf eine periodisch strukturierte Photolackschicht aufgedampft wurden. Für die bottom-OLEDs konnte für eine Gitterkonstante von 0.71 μm eine Steigerung der EQE um 27 %, verglichen zu einer optimierten unstrukturierten Referenz, ermittelt werden. Eine Vergrößerung der Gitterkonstante führt zu einer Abnahme der EQE. Die erhöhte EQE wird auf die Überlagerung des planaren Emissionsspektrums mit Beiträgen von Bragg-gestreuten, ursprünglich nicht-strahlenden Moden zurückgeführt, wobei die Intensitäten der Anteile von der Gitterkonstante und der Strukturhöhe abhängen. Für die top-OLEDs konnte eine Steigerung der EQE um 13 % für eine Gitterkonstante von 1.0 μm festgestellt werden. Im Gegensatz zu den bottom-OLEDs wird für kleinere Gitterkonstanten (0.6 μm) hier die EQE nicht erhöht. Vielmehr kommt es durch die starke Veränderung des Emissionsspektrums zu einer Erhöhung der photometrischen Lichtausbeute um 13.5 %. Die starke Veränderung des Emissionspektrums wird auf eine kohärente Kopplung zwischen den Bragg-gestreuten Moden zurückgeführt, bedingt durch die starke optische Mikrokavität dieses OLED-Typs. Um diese Effekte quantitativ zu beschreiben, wurde ein entsprechendes Modell entwickelt und implementiert. Die Qualität der Simulationsergebnisse wird anhand von Literaturreferenzen überprüft, wobei eine gute Übereinstimmung zu experimentell gemessenen Spektren erzeugt wird. Mit dem Simulationsmodell werden Vorhersagen über das Emissionspektrum und die resultierenden Effizienzen möglich. Für bottom-OLEDs wurde festgestellt, dass eine starke Veränderung des Emissionspektrums für Gitterkonstanten unterhalb von 0.5 μm erzeugt werden kann. Hingegen sind für top-OLEDs sehr schwache Strukturen oder große Gitterkonstanten notwendig, um eine nur schwache Veränderung des Emissionsspektrums und damit einen allgemeinen Effizienzgewinn zu erzeugen. Bezüglich der Gitterkonstante, ist diese Erkenntnis ist im Gegensatz zur üblichen Herangehensweise zur Implementierung periodischer Streuschichten in OLEDs. Mit der implementierten Simulationsmethode werden jedoch Aussagen bzgl. Emissionspektrum und Effizienz für eine breite Spanne an OLED-Strukturen vor der experimentellen Umsetzung möglich. / Organic light-emitting diodes (OLEDs) are an attractive new light source for display and lighting applications. In general, the light extraction from OLEDs is limited due to the high refractive index of the active emitter material and the thin film geometry. The high refractive index causes the trapping of a significant portion of the emitted light due to total internal reflection (TIR). Due to the thin film layout, the light emission is enhanced for resonant modes of the coherent optical microcavity, in particular for light affected by TIR. In this work two approaches are investigated in detail in order to increase the light extraction efficiency of OLEDs. In a first approach, the implementation of a low refractive index material next to the opaque metallic back-reflector is discussed. This modifies the dispersion relation of the non-radiative surface plasmon polariton (SPP) mode at the metal / dielectric interface, causing a shift of the SPPs dispersion relation. Thereby, the phase space into which power can be efficiently dissipated by the emitter is reduced. For the SPP this power would have been lost to the cavity, such that in total the outcoupling efficiency is increased. In experiment, an increased external quantum efficiency (EQE) is observed for an emitter exhibiting isotropic orientation of the sources (Ir(ppy)3 ,+19 %), as well as for an emitter which shows preferential horizontal orientation (Ir(ppy)2 (acac), +18 %), compared to an optimized device which uses standard material. This corresponds very well to the enhancement of the outcoupling efficiencies of the corresponding microcavities (+23 %, resp. +19 %) reducing the refractive index of the hole transport layer by 15 %. Optical simulations indicate that the approach is generally applicable to a wide range of device architectures. These in particular include OLEDs with emitters showing a perfectly horizontal alignment of their transition dipole moments. Furthermore, the approach is suitable for white OLEDs. Bragg scattering was investigated as second option to increase the light extraction from OLEDs. The method requires a periodically structured surface. For the bottom-emitting OLEDs, this is achieved by a direct laser interference patterning (DLIP) of the transparent electrode. Additionally, top-emitting devices were fabricated onto periodically corrugated photoresist layers. Using a periodic line pattern with a lattice constant of 0.71 μm, the EQE of the bottom-emitting devices was enhanced by 27 % compared to an optimized planar reference. For the bottom-emitting layout, increasing the lattice constant leads to lower EQEs. The increased EQE is attributed to the superposition of the radiative cavity resonances by Bragg scattered intensities of trapped modes. The intensities depend on the lattice constants as well as the height of the periodic surface perturbation. For top-emitting OLEDs comprising a lattice constant of 1.0 μm the EQE was increased by 13 %. Reducing the lattice constant (0.6 μm) decreases the EQE, albeit the luminous efficacy is increased by 13.5 % due to a heavily perturbed emission spectrum. The perturbation is attributed to a coherent interaction of the Bragg scattered modes due to the strong optical microcavity for the top-emitting OLEDs. Thus, for strong perturbation specific emission patterns can be achieved, but an overall enhanced efficiency is difficult to obtain. To investigate the observed results theoretically, a detailed simulation approach is outlined. The simulation method is carefully evaluated using reference data from literature. Using the simulation approach, the emission patterns as well as the efficiencies of the devices can be estimated. The emission spectra reproduced from simulation are in good agreement with the experiment. Furthermore, for the bottom-emitting layout, a strong interaction can be found from simulations for lattice constants below 0.5 μm. For top-emitting OLEDs, the weak interaction regime seems to be more likely to result in an overall enhanced emission. This requires, in contrast to conventional opinion, very shallow perturbations or lattice constants which exceed the peak wavelength of the emission spectrum. However, with the established simulation approach a-priori propositions on the emission spectrum or particular beneficial device layouts become feasible.

Thanks to its compatibility with the current CMOS technology and its potential of seamless integration with electronics, silicon photonics has been attracting an ever-increasing interest in recent years from both the academia and industry. By applying silicon photonic technology in microwave photonics, on-chip integration of microwave photonic systems could be implemented with improved performance including a much smaller size, better stability and lower power consumption. This thesis focuses on developing silicon-based photonic integrated circuits for microwave photonic applications. Two types of silicon-based on-chip devices, waveguide Bragg gratings and optical micro-cavity resonators, are designed, developed, and characterized, and the use of the developed devices in microwave photonic applications is studied. After an introduction to silicon photonics and microwave photonics in Chapter 1 and an overview of microwave photonic signal generation and processing in Chpater2, in Chapter 3 a silicon-based on-chip phase-shifted waveguide Bragg grating (PS-WBG) is designed, fabricated and characterized, and its use for the implementation of a photonic temporal differentiator is experimentally demonstrated. To have a waveguide grating that is wavelength tunable, in Chapter 4 a tunable waveguide grating is proposed by incorporating a PN junction across the waveguide grating, to use the free-carrier plasma dispersion effect in silicon to achieve wavelength tuning. The use of a pair of wavelength-tunable waveguide gratings to form a wavelength-tunable Fabry-Perot resonator for microwave photonic signal processing is studied. Thanks to its electrical tunability, a high-speed electro-optic modulator, a tunable fractional-order photonic temporal differentiator and a tunable optical delay line are experimentally demonstrated. To increase the bandwidth of a waveguide grating, in Chapter 5 a linearly chirped waveguide Bragg grating (LC-WBG) is designed, fabricated and evaluated. By incorporating two LC-WBGs in two arms of a Mach-Zehnder interferometer (MZI) structure, an on-chip optical spectral shaper is produced, which is used in a photonic microwave waveform generation system based on spectral-shaping and wavelength-to-time (SS-WTT) mapping for linearly chirped microwave waveform (LCMW) generation. To enable the LC-WBG to be electrically tuned, in Chapter 6 a lateral PN junction is introduced in the grating and thus an electrically tunable LC-WBG is realized. By incorporating two tunable LC-WBGs in a Michelson interferometer structure, an electrically tunable optical spectral shaper is made. By applying the fabricated spectral shaper in an SS-WTT mapping system, a continuously tunable LCMW is experimentally generated. Compared with a waveguide Bragg grating device, an on-chip optical micro-cavity resonator usually has a much smaller dimension, which is of help to increase the integration density and reduce the power consumption. Different on-chip optical micro-cavity resonators are studied in this thesis. In Chapter 7, an on-chip symmetric MZI incorporating multiple cascaded microring resonators is proposed. By controlling the radii of the rings, the MZI could be designed to have a spectral response with a linearly-varying free spectral range (FSR), which could be used in photonic generation of an LCMW, and to have a multi-channel spectral response with identical channel spacing, which could be used in the implementation of an independently tunable multi-channel fractional-order temporal differentiator. To further reduce the footprint of an optical micro-cavity resonator, in Chapter 8 an ultra-compact microdisk resonator (MDR) with a single-mode operation and an ultra-high Q-factor is proposed, fabricated and evaluated, and its use for the implementation of a microwave photonic filter and an optical delay line is experimentally demonstrated. To enable the MDR to be electrically tunable, in Chapter 9 an electrically tunable MDR is realized by incorporating a lateral PN junction in the disk. The use of the fabricated MDR in microwave photonic applications such as a high-speed electro-optic modulator, a tunable photonic temporal differentiator and a tunable optical delay line is experimentally demonstrated.

The unique properties, such as large direct bandgap, excellent thermal stability, high μH × ns, of III-nitrides make them ideal candidates for both optoelectronic and high-speed electronic devices. In the past decades, great success has been achieved in commercialization of GaN based light emitting diodes (LEDs) and laser diodes (LDs). However, due to the lack of native substrates, thin films grown on sapphire or SiC substrates have high defect densities that degrade the device performance and reliability. Conventional epitaxy lateral overgrowth (ELO) can reduce dislocation densities down to ∼10-6 cm-2 in the lateral growth area, but requires ex situ photolithography steps. Hence, an in situ method using a SiNx interlayer (nano-scale ELOG) has emerged as a promising technique. The GaN templates prepared by this method exhibit a very low dislocation density (low-10-7 cm-2) and excellent optical and electrical properties. As a cost, such high quality GaN templates containing SiN, nanonetworks are not suitable for heterojunction field effect transistor (HFET) applications due to degenerate GaN:Si layer which serves as parallel conduction channel. This dissertation discusses the growth of low dislocation density GaN templates, by using the in situ SiNx nanonetwork for conductive templates, and the AIN buffer for semi-insulating templates. On SiN x nanonetwork templates, double-barrier RTD and superlattice (SL) exhibited negative differential resistances. Moreover, the injection current of Blue LEDs (450 nm) was improved ∼30%. On semi-insulating GaN templates, nearly lattice matched AlInN/AIN/GaN HFETs were successfully demonstrated and exhibited ∼ 1600 cm2/Vs and 17 600 cm2/Vs Hall mobilities at 300 K and 10 K, respectively. Those mobility values are much higher than literature reports and indicate that high quality HFETs can be realized in lattice matched AlInN/AIN/GaN, thereby solving the strain related issue. The attempt to use InGaN as the 2DEG channel has also been successfully implemented. A Hall mobility (1230 cm2/Vs) was achieved in a 12 nm InGaN channel HFET with AlInGaN barrier, which demonstrates the viability of InGaN channel HFETs.

Les microcavités à grand facteur de qualité et faible volume modal permettent, grâce à un fort effet de confinement de la lumière, le renforcement des interactions lumière-Matière et la réalisation de futurs dispositifs pour le traitement optique de l’information à faible énergie de commande. Ce travail de thèse traite du fonctionnement de microcavités à cristal photonique en régime d’excitation cohérente, basé sur des impulsions dont la relation temps-Fréquence est contrôlée afin de renforcer les interactions non linéaires intracavité.La modélisation de la dynamique non linéaire de ces cavités à l'aide de la théorie des modes couplés, a permis de mettre en avant le rôle des non-Linéarités réfractives sur la réduction des effets de localisation au cours de l'excitation.Nous proposons alors de contrôler la dynamique du champ intracavité par un contrôle de la relation temps-Fréquence des impulsions.Cette excitation dite cohérente, repose sur la mise en œuvre d'un montage de mise en forme d'impulsions, constitué d'un étireur d'impulsions et d'un dispositif de filtrage spectral.La caractérisation non linéaire de nanoguides en silicium a permis, en complément du modèle, la détermination précise des paramètres des impulsions.Nous avons ensuite réalisé la toute première démonstration expérimentale de l'excitation cohérente de microcavités, menant à la fois à un renforcement des interactions non linéaires et une réduction des distorsions subies par les impulsions transmises par la cavité. / High quality factor and small modal volume microcavities allow, thanks to a strong light confinement, an enhancement of light matter interactions and the realization of low energy consumption devices for optical signal processing.In this work, we study the coherent excitation of nonlinear photonic crystal resonators, which is achieved by controlling the pulse time-Frequency relation, enabling nonlinear interaction enhancement.A modeling of the intra-Cavity nonlinear dynamics is conducted using the coupled mode theory, underlying the nonlinear refractive effects contribution in the intra-Cavity pulse energy reduction and distortion.We show that an appropriate pulse time-Frequency relation allow to compensate for the cavity resonance frequency shift, and to maintain the benefit of light localization during the entire excitation.The pulse shaper, made of a pulse-Stretcher combined with a spectral filter, has been specifically designed.Preliminary nonlinear characterizations of silicon nanowires enable to determine the shaped pulses parameters.A very first experimental coherent excitation of an optical resonator is reported, leading to a nonlinear interaction enhancement, and to the control of both the optical bandwidth and nonlinear dynamics of the cavity.

Organische, lichtemittierende Dioden (OLEDs) bezeichnen neuartige Lichtquellen, welche zur Beleuchtung oder für Displayanwendungen nutzbar sind. Im Allgemeinen ist die Lichtausbeute durch den hohen Brechungsindex und die Dünnschichtgeometrie der OLED begrenzt. Der hohe Brechungsindex sorgt dafür, dass ein signifikanter Anteil des emittierten Lichts in der OLED durch Totalreflexion (TIR) gefangen ist. Durch den Dünnschichtaufbau der OLED wird außerdem die Lichterzeugung für resonante Moden der kohärenten optischen Mikrokavität erhöht. Dies gilt im Besonderen für die nichtstrahlenden Moden. In dieser Arbeit wurden zwei Methoden untersucht, um die Lichtausbeute aus OLEDs zu erhöhen. Zuerst wurde die Implementierung von Materialien mit niedrigem Brechungsindex angrenzend zum undurchsichtigen metallischen Rückkontakt untersucht. Die Modifizierung des Brechungindexes verändert die Dispersionsrelation der an der Grenzfläche zwischen Metall und Dielektrikum angeregten nicht-strahlenden Oberflächenplasmonpolariton-Resonanz (SPP). Dadurch wird der Phasenraum verkleinert, in welchen effizient Strahlung abgegeben werden kann. Da die SPP-Resonanz eine nichtstrahlende Verlustquelle der Mikrokavität darstellt, wird so die Auskopplungseffizienz der OLED erhöht. In experimentellen Umsetzungen konnte die externe Quanteneffizienz (EQE) sowohl für einen Emitter gesteigert werden, welcher eine isotrope Verteilung der Strahlungsquellen besitzt (Ir(ppy)3 , +19 %), als auch für eine vorzugsweise horizontale Ausrichtung (Ir(ppy)2 (acac), +18 %). Die Steigerung der EQE korrespondiert sehr gut mit der berechneten Steigerung der Auskopplungseffizienz für die jeweiligen Mikrokavitäten (+23 %, bzw. +19 %). Weitere optische Simulationen legen den Schluss nahe, dass dieser Ansatz ebenso für perfekt horizontale Ausrichtung der Quellen sowie für weiße OLEDs anwendbar ist. Als zweiter Ansatz wurde die erhöhte Lichtausbeute durch Bragg-Streuung an periodische Linienstrukturen untersucht. In dieser Arbeit wurden Methoden untersucht, bei denen die Oberflächen strukturiert wurde, auf welche die organischen Halbleiterschichten der OLEDs aufgebracht wurden. Für bottom-OLEDs (durch ein Substrat emittierende OLEDs), wurde direkt die transparente Elektrode durch ein Laserinterferenzablationsverfahren (DLIP) modifiziert. Zusätzlich wurden top-OLEDs untersucht (direkt aus der Mikrokavität Licht emittierende OLEDs), für welche alle Schichten auf eine periodisch strukturierte Photolackschicht aufgedampft wurden. Für die bottom-OLEDs konnte für eine Gitterkonstante von 0.71 μm eine Steigerung der EQE um 27 %, verglichen zu einer optimierten unstrukturierten Referenz, ermittelt werden. Eine Vergrößerung der Gitterkonstante führt zu einer Abnahme der EQE. Die erhöhte EQE wird auf die Überlagerung des planaren Emissionsspektrums mit Beiträgen von Bragg-gestreuten, ursprünglich nicht-strahlenden Moden zurückgeführt, wobei die Intensitäten der Anteile von der Gitterkonstante und der Strukturhöhe abhängen. Für die top-OLEDs konnte eine Steigerung der EQE um 13 % für eine Gitterkonstante von 1.0 μm festgestellt werden. Im Gegensatz zu den bottom-OLEDs wird für kleinere Gitterkonstanten (0.6 μm) hier die EQE nicht erhöht. Vielmehr kommt es durch die starke Veränderung des Emissionsspektrums zu einer Erhöhung der photometrischen Lichtausbeute um 13.5 %. Die starke Veränderung des Emissionspektrums wird auf eine kohärente Kopplung zwischen den Bragg-gestreuten Moden zurückgeführt, bedingt durch die starke optische Mikrokavität dieses OLED-Typs. Um diese Effekte quantitativ zu beschreiben, wurde ein entsprechendes Modell entwickelt und implementiert. Die Qualität der Simulationsergebnisse wird anhand von Literaturreferenzen überprüft, wobei eine gute Übereinstimmung zu experimentell gemessenen Spektren erzeugt wird. Mit dem Simulationsmodell werden Vorhersagen über das Emissionspektrum und die resultierenden Effizienzen möglich. Für bottom-OLEDs wurde festgestellt, dass eine starke Veränderung des Emissionspektrums für Gitterkonstanten unterhalb von 0.5 μm erzeugt werden kann. Hingegen sind für top-OLEDs sehr schwache Strukturen oder große Gitterkonstanten notwendig, um eine nur schwache Veränderung des Emissionsspektrums und damit einen allgemeinen Effizienzgewinn zu erzeugen. Bezüglich der Gitterkonstante, ist diese Erkenntnis ist im Gegensatz zur üblichen Herangehensweise zur Implementierung periodischer Streuschichten in OLEDs. Mit der implementierten Simulationsmethode werden jedoch Aussagen bzgl. Emissionspektrum und Effizienz für eine breite Spanne an OLED-Strukturen vor der experimentellen Umsetzung möglich.:1. Introduction 1.1. Motivation 1.2. Scope and outline of this work 2. Organic light emitting diodes - basic concepts 2.1. Amorphous organic semiconductors – electronic properties and transport of charge carriers 2.2. Charge injection into organic semiconductors 2.3. Doping of organic semiconductors and the p-i-n concept for OLEDs 2.4. Charge carrier recombination mechanisms 2.4.1. Displaced harmonic oscillator model for the photoluminescence spectrum of organic emitters 3. OLEDs from thin homogeneous films - theoretical introduction into the optics 3.1. Maxwell’s equations 3.1.1. Boundary conditions 3.1.2. Poynting’s theorem, energy density, and energy flux density 3.2. Optics of thin planar films 3.2.1. Plane waves solution for the homogeneous Maxwell’s equations 3.2.2. Transfer-matrix formalism 3.3. Radiation from electric dipoles embedded into stratified media 3.4. Remarks on the normalized power dissipation 3.5. Description of outcoupled light as resonances 3.6. Basics of optimizing efficiency of OLEDs 3.6.1. Efficiencies for OLED characterization 3.6.2. Optimization of light outcoupling of OLEDs 3.6.2.1. Optimization of the basic cavity layout 3.6.2.2. Optimization of the emitter distribution 3.6.3. Enhancing OLED efficiency beyond the planar limit 4. Experimental fabrication and characterisation methods 4.1. Fabrication methods for organic semiconductors 4.2. Electrical and optical characterisation 4.3. Experimental realization of periodic corrugated surfaces 5. Enhancing the outcoupling efficiency by introducing low-refractive index layers 5.1. Dispersion relations of surface plasmon polaritons in thin film optical microcavities 5.1.1. Bulk surface plasmon polaritons 5.1.2. Coupled surface plasmon polariton states for thin film geometries 5.2. Theoretical potential for outcoupling enhancement due to low refractive index interlayers 5.3. Experimental validation for top-emitting OLEDs with isotropic or anisotropic green phosphorescent emitter 6. Bragg scattering for improved light outcoupling from OLEDs 6.1. Field expansion for periodic photonic crystals 6.2. Bragg scattering in weakly periodically perturbed bottom-emitting monochrome OLEDs 6.2.1. Device details and experimental characterization 6.2.2. Quantitative assignment of Bragg scattering effects within electroluminescence spectrum 6.3. Bragg scattering in top-emitting monochrome OLEDs 6.3.1. Device details and experimental characterization 6.3.2. Analysis of electroluminescence spectrum and description of scattered light from resonance model 6.4. Simulation of the spectral radiant intensity for periodically corrugated OLEDs 6.4.1. Theoretical flowchart 6.4.2. Preliminaries and source representation 6.4.2.1. Plane wave expansion and z-depended field coefficient representation 6.4.2.2. Pseudo-periodic polarization source 6.4.2.3. Solution to the inhomogeneous Maxwell’s equations for a pseudo-periodic source 6.4.3. Field propagation and scattering matrix 6.4.3.1. Reducing the Maxwell’s equation 6.4.3.2. Representation-transformation matrices 6.4.3.3. Formulation of transfer-matrix formalism for periodically perturbed media 6.4.3.4. Iterative calculation of the scattering matrix in plane wave basis 6.4.4. From electromagnetic fields to measurement 6.4.4.1. Far-field solutions in superstrate/substrate media 6.4.4.2. System matrix for pseudo-periodic sources within periodically corrugated cavity 6.4.4.3. Radiant intensity from far-field solutions 6.4.4.4. Treatment of incoherent thick superstrate and substrate 6.4.4.5. Including electroluminescence spectra of organic emitter materials 6.5. Simulation of light emission from emitters embedded into periodically perturbed microcavities 6.5.1. Comparison to experimental data and existing simulation approaches 6.5.2. Simulated light emission for periodically perturbed microcavities 6.5.2.1. Simulation of light emission from corrugated bottom-emitting OLEDs 6.5.2.2. Comparing simulation to experiment for top-emitting OLEDs on corrugated photoresist 6.5.3. A-priori simulation of optical microcavities 6.5.3.1. Variation of lattice constant and aspect ratio to maximize total radiant intensity 7. Conclusions 8. Outlook Appendices A. Materials – Abbreviations and optoelectronic modeling parameters A.1. Organic semiconductors and ZnO:Al A.1.1. Active emitter materials A.1.2. Dielectric functions A.2. Metals B. Power dissipation spectra and oSPP shifts for top- and bottom-emitting OLEDs incorporating silver and aluminum anode layers C. Further comments on theoretical derivations leading to the simulation of emission from photonic crystal optical microcavities C.1. Numerical approximation of the integration of Maxwell’s equation C.2. Details on the far-field approximation of the periodic plane wave expansion C.3. Derivation of the efficient iterative calculation scheme for the scattering-matrix C.4. On the equality of the two system matrices C.5. Calculation of the complete scattering-matrix for the passive periodically perturbed microcavity Bibliography / Organic light-emitting diodes (OLEDs) are an attractive new light source for display and lighting applications. In general, the light extraction from OLEDs is limited due to the high refractive index of the active emitter material and the thin film geometry. The high refractive index causes the trapping of a significant portion of the emitted light due to total internal reflection (TIR). Due to the thin film layout, the light emission is enhanced for resonant modes of the coherent optical microcavity, in particular for light affected by TIR. In this work two approaches are investigated in detail in order to increase the light extraction efficiency of OLEDs. In a first approach, the implementation of a low refractive index material next to the opaque metallic back-reflector is discussed. This modifies the dispersion relation of the non-radiative surface plasmon polariton (SPP) mode at the metal / dielectric interface, causing a shift of the SPPs dispersion relation. Thereby, the phase space into which power can be efficiently dissipated by the emitter is reduced. For the SPP this power would have been lost to the cavity, such that in total the outcoupling efficiency is increased. In experiment, an increased external quantum efficiency (EQE) is observed for an emitter exhibiting isotropic orientation of the sources (Ir(ppy)3 ,+19 %), as well as for an emitter which shows preferential horizontal orientation (Ir(ppy)2 (acac), +18 %), compared to an optimized device which uses standard material. This corresponds very well to the enhancement of the outcoupling efficiencies of the corresponding microcavities (+23 %, resp. +19 %) reducing the refractive index of the hole transport layer by 15 %. Optical simulations indicate that the approach is generally applicable to a wide range of device architectures. These in particular include OLEDs with emitters showing a perfectly horizontal alignment of their transition dipole moments. Furthermore, the approach is suitable for white OLEDs. Bragg scattering was investigated as second option to increase the light extraction from OLEDs. The method requires a periodically structured surface. For the bottom-emitting OLEDs, this is achieved by a direct laser interference patterning (DLIP) of the transparent electrode. Additionally, top-emitting devices were fabricated onto periodically corrugated photoresist layers. Using a periodic line pattern with a lattice constant of 0.71 μm, the EQE of the bottom-emitting devices was enhanced by 27 % compared to an optimized planar reference. For the bottom-emitting layout, increasing the lattice constant leads to lower EQEs. The increased EQE is attributed to the superposition of the radiative cavity resonances by Bragg scattered intensities of trapped modes. The intensities depend on the lattice constants as well as the height of the periodic surface perturbation. For top-emitting OLEDs comprising a lattice constant of 1.0 μm the EQE was increased by 13 %. Reducing the lattice constant (0.6 μm) decreases the EQE, albeit the luminous efficacy is increased by 13.5 % due to a heavily perturbed emission spectrum. The perturbation is attributed to a coherent interaction of the Bragg scattered modes due to the strong optical microcavity for the top-emitting OLEDs. Thus, for strong perturbation specific emission patterns can be achieved, but an overall enhanced efficiency is difficult to obtain. To investigate the observed results theoretically, a detailed simulation approach is outlined. The simulation method is carefully evaluated using reference data from literature. Using the simulation approach, the emission patterns as well as the efficiencies of the devices can be estimated. The emission spectra reproduced from simulation are in good agreement with the experiment. Furthermore, for the bottom-emitting layout, a strong interaction can be found from simulations for lattice constants below 0.5 μm. For top-emitting OLEDs, the weak interaction regime seems to be more likely to result in an overall enhanced emission. This requires, in contrast to conventional opinion, very shallow perturbations or lattice constants which exceed the peak wavelength of the emission spectrum. However, with the established simulation approach a-priori propositions on the emission spectrum or particular beneficial device layouts become feasible.:1. Introduction 1.1. Motivation 1.2. Scope and outline of this work 2. Organic light emitting diodes - basic concepts 2.1. Amorphous organic semiconductors – electronic properties and transport of charge carriers 2.2. Charge injection into organic semiconductors 2.3. Doping of organic semiconductors and the p-i-n concept for OLEDs 2.4. Charge carrier recombination mechanisms 2.4.1. Displaced harmonic oscillator model for the photoluminescence spectrum of organic emitters 3. OLEDs from thin homogeneous films - theoretical introduction into the optics 3.1. Maxwell’s equations 3.1.1. Boundary conditions 3.1.2. Poynting’s theorem, energy density, and energy flux density 3.2. Optics of thin planar films 3.2.1. Plane waves solution for the homogeneous Maxwell’s equations 3.2.2. Transfer-matrix formalism 3.3. Radiation from electric dipoles embedded into stratified media 3.4. Remarks on the normalized power dissipation 3.5. Description of outcoupled light as resonances 3.6. Basics of optimizing efficiency of OLEDs 3.6.1. Efficiencies for OLED characterization 3.6.2. Optimization of light outcoupling of OLEDs 3.6.2.1. Optimization of the basic cavity layout 3.6.2.2. Optimization of the emitter distribution 3.6.3. Enhancing OLED efficiency beyond the planar limit 4. Experimental fabrication and characterisation methods 4.1. Fabrication methods for organic semiconductors 4.2. Electrical and optical characterisation 4.3. Experimental realization of periodic corrugated surfaces 5. Enhancing the outcoupling efficiency by introducing low-refractive index layers 5.1. Dispersion relations of surface plasmon polaritons in thin film optical microcavities 5.1.1. Bulk surface plasmon polaritons 5.1.2. Coupled surface plasmon polariton states for thin film geometries 5.2. Theoretical potential for outcoupling enhancement due to low refractive index interlayers 5.3. Experimental validation for top-emitting OLEDs with isotropic or anisotropic green phosphorescent emitter 6. Bragg scattering for improved light outcoupling from OLEDs 6.1. Field expansion for periodic photonic crystals 6.2. Bragg scattering in weakly periodically perturbed bottom-emitting monochrome OLEDs 6.2.1. Device details and experimental characterization 6.2.2. Quantitative assignment of Bragg scattering effects within electroluminescence spectrum 6.3. Bragg scattering in top-emitting monochrome OLEDs 6.3.1. Device details and experimental characterization 6.3.2. Analysis of electroluminescence spectrum and description of scattered light from resonance model 6.4. Simulation of the spectral radiant intensity for periodically corrugated OLEDs 6.4.1. Theoretical flowchart 6.4.2. Preliminaries and source representation 6.4.2.1. Plane wave expansion and z-depended field coefficient representation 6.4.2.2. Pseudo-periodic polarization source 6.4.2.3. Solution to the inhomogeneous Maxwell’s equations for a pseudo-periodic source 6.4.3. Field propagation and scattering matrix 6.4.3.1. Reducing the Maxwell’s equation 6.4.3.2. Representation-transformation matrices 6.4.3.3. Formulation of transfer-matrix formalism for periodically perturbed media 6.4.3.4. Iterative calculation of the scattering matrix in plane wave basis 6.4.4. From electromagnetic fields to measurement 6.4.4.1. Far-field solutions in superstrate/substrate media 6.4.4.2. System matrix for pseudo-periodic sources within periodically corrugated cavity 6.4.4.3. Radiant intensity from far-field solutions 6.4.4.4. Treatment of incoherent thick superstrate and substrate 6.4.4.5. Including electroluminescence spectra of organic emitter materials 6.5. Simulation of light emission from emitters embedded into periodically perturbed microcavities 6.5.1. Comparison to experimental data and existing simulation approaches 6.5.2. Simulated light emission for periodically perturbed microcavities 6.5.2.1. Simulation of light emission from corrugated bottom-emitting OLEDs 6.5.2.2. Comparing simulation to experiment for top-emitting OLEDs on corrugated photoresist 6.5.3. A-priori simulation of optical microcavities 6.5.3.1. Variation of lattice constant and aspect ratio to maximize total radiant intensity 7. Conclusions 8. Outlook Appendices A. Materials – Abbreviations and optoelectronic modeling parameters A.1. Organic semiconductors and ZnO:Al A.1.1. Active emitter materials A.1.2. Dielectric functions A.2. Metals B. Power dissipation spectra and oSPP shifts for top- and bottom-emitting OLEDs incorporating silver and aluminum anode layers C. Further comments on theoretical derivations leading to the simulation of emission from photonic crystal optical microcavities C.1. Numerical approximation of the integration of Maxwell’s equation C.2. Details on the far-field approximation of the periodic plane wave expansion C.3. Derivation of the efficient iterative calculation scheme for the scattering-matrix C.4. On the equality of the two system matrices C.5. Calculation of the complete scattering-matrix for the passive periodically perturbed microcavity Bibliography

Ce manuscrit est consacré à la physique des polaritons dans deux matériaux semiconducteurs à grand gap : ZnO et GaN. Les paramètres polaritoniques de ces matériaux ont été déterminés avec précision grâce à une étude combinant différentes techniques spectroscopiques linéaires et non-linéaires (réflectivité continue, autocorrélation, photoluminescence et mélange à quatre ondes dégénérées). L’interprétation de ces résultats conduit à une meilleure compréhension des processus d’interaction au sein du semiconducteur : le rôle important des interactions polariton-phonon LO dans l’élargissement polaritonique a notamment pu être mis en évidence. Ce travail effectué sur des échantillons massifs est indispensable pour mener au mieux l’étude de l’effet laser à polaritons dans des microcavités présentée dans la seconde partie de ce manuscrit. Pour cette étude, deux microcavités massives semblables, une à base de ZnO l’autre de GaN, ont été réalisées. Les qualités photoniques de ces structures sont à l’état de l’art : elles présentent un bon facteur de qualité (Q ≈ 1000) et un faible désordre photonique. Le régime de couplage fort ainsi que l’effet laser à polaritons sont observés jusqu'à température ambiante. Enfin, l’établissement de diagrammes de phases permet de mettre en exergue le rôle important des phonons LO dans l’abaissement du seuil laser. / This manuscript is devoted to the physics of polaritons in two wide band gap semiconductor : ZnO and GaN. The polaritonic parameters of these materials have been accurately determined through a study which combines linear and non-linear spectroscopies (continuous reflectivity, autocorrelation, photoluminescence and degenerate four-wave mixing). The interpretation of these results lead to a better understanding of the interaction processes in the semiconductor : the important role played by the polariton-LO phonon interactions in the polaritonic damping is highlighted and particularly for ZnO. This preliminary work on bulk samples is essential for a suitable study of polariton lasing in microcavities like it is presented in the second part of this manuscript. For this study, two similar microcavities, one based on ZnO and another on GaN. The photonic properties of these structures are at the state of the art : they have a good quality factor (Q ≈ 1,000) and have a low photon disorder. The strong coupling regime and the polariton lasing are observed to room temperature. Finally, the establishment of phase diagrams allows to highlight the important role of LO phonons in reduction of the laser threshold.

Avec l’évolution rapide des techniques de nanofabrication et les besoins croissants d’intégration et d’utilisation à moindre cout énergétique, l’étude et la manipulation de résonances électromagnétiques d’objets de faibles dimensions représentent des enjeux cruciaux. Un des objectifs de ce travail de thèse a donc été d’approfondir nos connaissances de l’interaction entre le champ électromagnétique et la matière. Dans ce but la réalisation conjointe d’expériences en champ proche optique et le développement numérique de modèles associés nous ont permis d’étudier différentes résonances électromagnétiques basées sur l’interaction lumière-matière au sein d’objets de dimensions sub-micrométriques. Dans une première partie, ce manuscrit présente les phénomènes mis en jeu en microscopie champ proche optique et décrit le fonctionnement du microscope SNOM utilise. La seconde partie est dédiée à l’étude de l’interaction d’une sonde champ proche avec une nano-cavité Fabry-Perot en régime non-linéaire. Dans un premier temps, on présente l’étude des non-linéarités de nano-cavités en Silicium à grand facteur de qualité et faible volume modal, démontrant ainsi l’obtention d’un régime de fonctionnement bistable pour de très faibles puissances. Dans un deuxième temps, on démontre la modulation possible via la sonde champ proche de ce régime de bistabilité. Enfin, on étudie dans la troisième partie de ce manuscrit les résonances de films minces métalliques. L’étude complète des modes propres et de l’excitation optique de cette structure a permis de connaitre avec précision les modes résonants et les angles de Brewster du film mince. Cette étude a été prolongée expérimentalement par l’étude en champ proche optique des modes résonants de demi-films minces métalliques. Lors de ces deux études, les mesures expérimentales ont été systématiquement accompagnées par l’analyse théorique et le développement numérique de modèles que les expériences réalisées ont permis de valider et de discuter. / Within the quick nano-fabrication techniques evolution and the increasing needs in low space and energy opto-electronic functions on-chip integration, studies and control of electromagnetic resonances of sub-micrometric objects are crucial issues. One aim of this work was then to improve our knowledge of the light-matter interaction. To this end, optical near-field experiments and complementary numerical development of models have been performed to study electromagnetic resonances due to light-matter interaction in sub-micrometric resonators. As an introduction, the first part of the manuscript presents the main phenomena involved in near-field optical microscopy and the used SNOM operation. The second part is dedicated to nearfield tip/Fabry-Perot micro-resonator interaction in the non-linear regime. In this part, we first present the study of high-Q/small volume Silicon nano-cavity non-linearities, showing possible bistable operation at very low incident power. We then demonstrate the cavity stability modulation obtain with the near-field tip. In the third part of the manuscript, we consider thin metallic film resonances. As a beginning, we realize an exhaustive study of the film eigenmodes and then discuss the resonant optical excitation of the film as well as precise determination of Brewster angle. These theoretical studies have been extended experimentally with the optical near-field determination of the resonant modes of semi-infinite thin films. For the different studies, experimental measures have been systematically associated with theoretical analyses and numerical developments of models, which have then been confirmed or discussed in light of the experimental results.