Résumé : Les circuits photoniques intégrés qui combinent des dispositifs photoniques pour la génération, la détection, la modulation, l'amplification, la commutation et le transport de la lumière dans une puce, ont été rapportés comme étant une innovation technologique importante qui simplifie la conception du système optique et qui réduit l'espace et la consommation de l'énergie en améliorant ainsi la fiabilité. La capacité de modifier la bande interdite des zones sélectives des différents dispositifs photoniques à travers la puce est la clé majeure pour le développement de circuits photoniques intégrés. Comparé à d'autres méthodes d’épitaxie, l’interdiffusion de puits quantiques a attiré beaucoup d'intérêt en raison de sa simplicité et son efficacité en accordant la bande interdite durant le processus de post-épitaxie. Cependant, l’interdiffusion de puits quantiques a subi des problèmes reliés au manque de précision pour modifier convenablement la bande interdite ciblée et à l’incontrôlabilité de l’absorption des impuretés au cours du processus qui peut dégrader la qualité du matériel interdiffusé. Dans cette thèse, nous avons utilisé les lasers excimer pour créer des défauts à proximité de la surface (~ 10 nm) des microstructures à base de puits quantiques III-V (par exemple InP et GaAs) et pour induire l’interdiffusion après le recuit thermique. L'irradiation par les lasers excimer (ArF et KrF) des microstructures à puits quantiques a été réalisée dans différents environnements, y compris l'air, l'eau déionisée, les couches diélectriques (SiO2 et Si3N4) et les couches d’InOx. Pour proposer un bon contrôle de la technique d’interdiffusion de puits quantiques par laser excimer, nous avons étudié la génération et la diffusion de défauts de surface en utilisant différentes méthodes de caractérisation de surface/interface, comme l'AFM, SEM, XPS et SIMS qui ont été utilisées pour analyser la modification de la morphologie de surface/interface et la modification chimique de la microstructure de ces puits quantiques. La qualité des microstructures à puits quantiques étudiées a été représentée par des mesures de photoluminescence et de luminescence des diodes lasers ainsi fabriqués. Les résultats montrent que le laser excimer induit des quantités d'oxydes de surface dans les surfaces des microstructure à puits quantiques InP/InGaAs/InGaAsP dans l'air et des impuretés d'oxygène des couches d'oxydes diffusées dans la région active de la microstructure lors du recuit, ce qui améliore l’interdiffusion, mais réduit l'intensité de la photoluminescence. Par contre, l’irradiation dans un environnement d'eau déionisée n’a pas démontré de diffusion des impuretés évidentes d'un excès d'oxygène vers les régions actives, mais la stœchiométrie de surface a été restaurée après l’interdiffusion. L’InOx a été trouvé avec un grand coefficient de dilatation thermique dans la microstructure interdiffusée qui était supposée d’augmenter la contrainte de compression dans la région active et ainsi d’augmenter l'intensité de photoluminescence de 10 fois dans l’échantillon irradié dans l'eau déionisée. Concernant les microstructures avec une couche diélectrique, la modification de la bande interdite a été toujours réalisée sur des échantillons dont les couches diélectriques ont été irradiées et la surface de InP a été modifiée par le laser excimer. Pour l'échantillon avec une couche de 243 nm de SiO2, les variations de la photoluminescence ont été mesurées sans l’ablation de cette couche de SiO2 lors de l'irradiation par le laser KrF. Cependant, la morphologie de l'interface d’InP a été modifiée, les oxydes d'interface ont été générés et les impuretés d'oxygène se sont diffusées à l'intérieur des surfaces irradiées. Les améliorations de l’interdiffusion dans les deux surfaces non irradiées et irradiés de l'échantillon couvert de couche d’InOx ont démontré l'importance des oxydes dans l’interdiffusion des puits quantiques. Les diodes laser fabriquées à partir d’un matériau interdiffusé par un laser KrF ont montré un seuil de courant comparable à celui des matériaux non interdiffusés avec un décalage de photoluminescence de 100 nm. En combinant un masque d'aluminium, nous avons créé un déplacement uniforme de photoluminescence de 70 nm sur une matrice rectangulaire de 40 μm x 200 μm ce qui présente un potentiel d’application de l’interdiffusion des puits quantiques par les lasers excimer dans les circuits photoniques intégrés. En outre, les lasers excimer ont été utilisés pour créer des structures de nano-cônes auto-organisées sur des surfaces de microstructure de InP/InGaAs/InGaAsP en augmentant l'intensité de PL par ~ 1.4 fois. Les lasers excimer ont été aussi utilisés pour modifier la mouillabilité sélective des zones d’une surface de silicium par une modification chimique de surface induite par laser dans différents milieux liquides. Ainsi, la fluorescence des nanosphères a été réussie pour des fonctions de configuration spécifique avec une surface de silicium. // Abstract : Photonic integrated circuits (PICs) which combine photonic devices for generation, detection, modulation, amplification, switching and transport of light on a chip have been reported as a significant technology innovation that simplifies optical system design, reduces space and power consumption, improves reliability. The ability of selective area modifying the bandgap for different photonic devices across the chip is the important key for PICs development. Compared with other growth methods, quantum well intermixing (QWI) has attracted amounts of interest due to its simplicity and effectiveness in tuning the bandgap in post-growth process. However, QWI has suffered problems of lack of precision in achieving targeted bandgap modification and uncontrollable up-taking of impurities during process which possibly degrade the quality of intermixed material. In this thesis, we have employed excimer laser to create surface defects in the near surface region (~ 10 nm) of III-V e.g. InP and GaAs, based QW microstructure and then annealing to induce intermixing. The irradiation by ArF and KrF excimer lasers on the QW microstructure was carried out surrounded by different environments, including air, DI water, dielectric layers (SiO2 and Si3N4) and InOx coatings. To propose a more controllable UV laser QWI technique, we have studied surface defects generation and diffusion with various surface/interface characterization methods, like AFM, SEM, XPS and SIMS, which were used to analyse the QW surface/interface morphology and chemical modification during QWI. The quality of processed QW microstructure was represented by photoluminescence measurements and luminescence measurements of fabricated laser diodes. The results shows that excimer laser induced amounts of surface oxides on the InP/InGaAs/InGaAsP microstructure surface in air and the oxygen impurities from oxides layer diffused to the active region of the QW microstructure during annealing, which enhance intermixing but also reduce the PL intensity. When irradiated in DI water environment, no obvious excessive oxygen impurities were found to diffuse to the active regions and the surface stoichiometry has been restored after intermixing. InOx with large coefficient of thermal expansion was found inside the intermixed QW microstructure, which was supposed to increase the compressive strain in active region and enhance the PL intensity to maximum 10 times on sample irradiated in DI water. On microstructure coated with dielectric layers, bandgap modifications were always found on samples whose dielectric layers were ablated and InP surface was modified by excimer laser. On sample coated with 243 nm SiO2 layer, the PL shifts were found on sample without ablation of the SiO2 layer when irradiated by KrF laser. However, the InP interface morphology was modified, interface oxides were generated and oxygen impurities have diffused inside on the irradiated sites. The enhancements of interdiffusion on both non irradiated and irradiated sites of sample coated with InOx layer have verified the importance of oxides in QWI. The laser diodes fabricated from KrF laser intermixed material have shown comparable threshold current density with as grown material with PL shifted by 133 nm. Combined aluminum mask, we have created uniform 70 nm PL shifts on 40 μm x 200 μm rectangle arrays which presents UV laser QWI potential application in PICs. In addition, excimer lasers have been used to create self organized nano-cone structures on the surface of InP/InGaAs/InGaAsP microstructure and enhance the PL intensity by ~1.4x. Excimer lasers have selective area modified wettability of silicon surface based on laser induced surface chemical modification in different liquid environments. Then the fluorescence nanospheres succeeded to specific pattern functions with silicon surface.

The ability to fabricate semiconductor wafers with spatially selected regions of different bandgap material is required for the fabrication of monolithic photonic integrated circuits (PIC's). Although this subject has been studied for three decades and many semiconductor engineering approaches have been proposed, the problem of achieving reproducible results has constantly challenged scientists and engineers. This concerns not only the techniques relaying on multiple sequential epitaxial growth and selective area epitaxy, but also the conventional quantum well intermixing (QWI) technique that has been investigated as a post-growth approach for bandgap engineering. Among different QWI techniques, those based on the use of different lasers appear to be attractive in the context of high-precision and the potential for cost-effective bandgap engineering. For instance, a tightly focused beam of the infrared (IR) laser could be used for the annealing of small regions of a semiconductor wafer comprising different quantum well (QW) or quantum dot (QD) microstructures. The precision of such an approach in delivering wafers with well defined regions of different bandgap material will depend on the ability to control the laser-induced temperature, dynamics of the heating-cooling process and the ability to take advantage of the bandgap engineering diagnostics. In the frame of this thesis, I have investigated IR laser-induced QWI processes in QW wafers comprising GaAs/A1GaAs and InP/InGaAsP microstructures and in InAs QD microstructures grown on InP substrates. For that purpose, I have designed and set up a 2-laser system for selective area rapid thermal annealing (Laser-RTA) of semiconductor wafers. The advantage of such an approach is that it allows carrying out annealing with heating-cooling rates unattainable with conventional RTA techniques, while a tightly focused beam of one of the IR lasers is used for `spot annealing'. These features have enabled me to introduce a new method for iterative bandgap engineering at selected areas (IBESA) of semiconductor wafers. The method proves the ability to deliver both GaAs and InP based QW/QD wafers with regions of different bandgap energy controlled to better than « 1nm of the spectral emission wavelength. The IBESA technique could be used for tuning the optical characteristics of particular regions of a QW wafer prepared for the fabrication of a PIC. Also, this approach has the potential for tuning the emission wavelength of individual QDs in wafers designed, e.g., for the fabrication of single photon emitters. In the 1st Chapter of the thesis, I provide a short review of the literature on QWI techniques and I introduce the Laser - RTA method. The 2nd Chapter is devoted to the description of the fundamental processes related to the absorption of laser light in semiconductors. I also discuss the results of the finite element method applied for modeling and semi-quantitative description of the Laser - RTA process. Details of the experimental setup and developed procedures are provided in the 3rd Chapter. The results concerning direct bandgap engineering and iterative bandgap engineering are discussed in the 4th and 5th Chapters, respectively.

Functional crystalline oxides with perovskite structure have a wide range of electrical properties such as ferroelectric, ferromagnetic, and superconductive, as well as unique properties that make them suited for a wide variety of applications including electro-optics, high-k dielectrics, and catalysis. Therefore, in order to realize the potential of perovskite oxides it is desirable to integrate them with semiconductors. Due to the high surface energy of oxides compared to that of semiconductors and the low number of oxides that are thermodynamically stable against SiO₂ formation, it has been extremely difficult to integrate epitaxial oxides with Si directly. However, in 1998, McKee and co-workers finally succeeded in depositing SrTiO₃ on Si directly using a Sr template via molecular beam epitaxy. This breakthrough opened the possibility of integrating the perovskite oxides with Si to realize potential device applications. In this dissertation, alkaline earth metal (Sr and Ba) templates on semiconductors, which enable epitaxial growth of complex oxides on semiconductors, are investigated using molecular beam epitaxy (MBE) for growth and in-situ X-ray/ultraviolet photoemission spectroscopy (XPS/UPS) for the electronic structure analysis. An epitaxial layer of SrTiO₃ on Si using such alkaline earth templates is used as a pseudo-substrate for the integration of perovskite oxides on Si. Through the use of post-deposition annealing as a function of oxygen pressure and annealing time, the strain relaxation behavior of epitaxial SrTiO₃ films grown on Si is also investigated to determine how the SiO₂ interlayer thickness affects the SrTiO₃ lattice constant. This ability to control strain relaxation can be used as a way to manipulate the properties of other perovskite oxides grown on SrTiO₃/Si. Additionally, SrTiO₃ can be made conductive by doping with La. Conductive SrTiO₃ can be used as a thermoelectric, a transparent conductive layer, and a quantum metal layer in a quantum metal field-effect transistor (QMFET). The structural, electrical, and optical properties of strained conductive La-doped SrTiO₃ are studied in order to understand the relation between elastic strain and electrical properties for electronic device applications. Oxide quantum well systems based on LaAlO₃/SrTiO₃ are also investigated using spectroscopic ellipsometry to understand how the quantum well layer structure affects the electronic structure. Such quantum well systems are good candidates for the monolithic integration of functional perovskites on semiconductors. Oxides quantum wells can be used in various device applications such as in quantum well cascade lasers, laser diodes and high performance transistors. As part of the growth optimization for high quality complex oxide heterostructures, the surface preparation of SrTiO₃ substrates using several different methods was also extensively studied using angle-resolved photoemission spectroscopy (ARPES). We found that acid-free water-based surface preparation is actually more effective at removing SrOx̳ crystallites and leaving the surface TiO₂-terminated compared to the more commonly used acid-based methods. / text

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

Neste trabalho, apresentamos estudos sobre o magnetotransporte em um sistema de bicamadas com uma rede de antipontos triangulares em campos magnéticos baixos sob a aplicação de campos elétricos externos, que são produzidos por voltagens de porta. A bicamada é feita em poços quânticos largos (wide quantum well) de alta densidade eletrônica, formado em heteroestruturas semicondutoras de AlxGa1xAs=GaAs. Oscila- ções magneto-inter-sub-banda (MIS) são observadas em poços quânticos largos de alta densidade eletrônica com duas sub-bandas ocupadas. Estas são originadas pelo espalhamento inter-sub-bandas e tem um máximo para campos magnéticos B que satisfazem a condição de alinhamento entre os leques dos níveis de Landau de cada sub-banda. Oscila- ções de comensurabilidade são observadas na magnetoresistência que é sensível ao arranjo do potencial dos antipontos. A aplicação de campos elétricos faz diminuir o número de oscilações na magnetoresistência para campos magnéticos compreendidos entre 0; 1T e 0; 4T, observando-se uma transição das oscilações MIS aos efeitos de comensurabilidade. Aplicando voltagens de porta podemos variar a amplitude do potencial dos antipontos. / In this work, we present studying about magnetotransport in a bilayer system with triangular antidot lattices in low magnetic elds under the application of external electric eld. The bilayer forms inside a wide quantum well of high electron density in semiconductor heterostructures formed by AlxGa1xAs=GaAs. Magneto-inter-subband (MIS) oscillations are observed in a wide quantum wells of high electron density with two subbands occupied, and they are caused by intersubband scattering and have a maximum for a magnetic eld B that satises the alignment condition between the staircase of Landau level. Commensurability oscillations are observed in magnetoresistance, which is sensitive to the potential of antidot arrangements. The application of electric elds decrease the number of oscillations in the magnetoresistance for magnetic elds between 0; 1T and 0:4T, showing a transition of MIS oscillations to commensurability oscillations. We varied the amplitude of the potential of the antidots applying dierent gate voltages.

Single-photon sources are essential building blocks in quantum photonic networks, where quantum-mechanical properties of photons are utilised to achieve quantum technologies such as quantum cryptography and quantum computing. In this thesis, a single-photon source driven by a surface acoustic wave (SAW) is developed and characterised. This single-photon source is based on a SAW-driven lateral n-i-p junction in a GaAs quantum-well structure. On this device, the lateral n-i-p junction is formed by gate-induced electrons and holes in two adjacent regions. The SAW potential minima create dynamic quantum dots in a 1D channel between these two regions, and are able to transport single electrons to the region of holes along the channel. Single-photon emission can therefore be generated as these electrons consecutively recombine with holes. After characterisation and optimisation in four batches of devices, clear SAW-driven charge transport and the corresponding electroluminescence (EL) can be observed on an optimised SAW-driven n-i-p junction. Time-resolved measurements have been carried out to study the dynamics of SAW-driven electrons. Time-resolved EL signals indicate that a packet of electrons is transported to the region of holes in each SAW minimum. In addition, the carrier lifetime of SAW-driven electrons in the region of holes is shown to be $\sim 100$ ps, which is much shorter than the SAW period of $860$ ps. Hence, it is promising to observe single-photon emission in the optimised device. In order to test single-photon emission, a Hanbury Brown-Twiss experimental setup has been employed to record an autocorrelation histogram of the SAW-driven EL signal at the single-electron regime. Suppression of autocorrelation coincidences at time delay $\Delta t = 0$ is evidence of photon antibunching. By fitting theoretical functions describing the SAW-driven EL signal, it is found that the second-order correlation function shows $g^{(2)}(0) = 0.39 \pm 0.05$, which is lower than the common criterion for a single-photon source $g^{(2)}(0) < 0.5$. Moreover, theoretical calculation and simulation suggest that, if a constant background signal can be filtered out, $\sim 80 \%$ of the SAW-driven EL is single-photon emission.

Vertical-cavity lasers (VCLs) are of great interest as lightsources for fiber-optic communication systems. Such deviceshave a number of advantages over traditional in-plane laserdiodes, including low power consumption, efficient fibercoupling, on-chip testability, as well as potential low-costfabrication and packaging. To date, GaAs-based VCLs operatingat 850 nm are the technology of choice for short-distance,high-speed data transmission over multimode fiber. Forlong-distance communication networks, long-wavelength (LW) VCLsoperating in the 1.3 and 1.55-&amp;#956m transmission windowsof standard singlemode fibers are desired. However, despiteconsiderable worldwide development efforts, the commercialbreakthrough of such devices has still to be achieved. This ismainly due to shortcomings of the intrinsic material propertiesof InP-based material systems, traditionally employed in LWlaser diodes. While LW quantum well (QW) active regions basedon InP are well established, efficient distributed Braggreflectors (DBRs) are better built up in the AlGaAs/GaAsmaterial system. Therefore, earlier work on LW VCLs has focusedon hybrid techniques such as bonding between InP-based QWs andAlGaAs/GaAs DBRs using waferfusion. More recently, however, themain interest in this field has shifted towards all-epitaxialGaAs-based devices employing novel 1.3-&amp;#956m activematerials with strained GaInNAs QWs as one of the mostpromising candidates. The main focus of this thesis is on the characterization andanalysis of LW VCLs and building blocks thereof, based on bothInP and GaAs substrates. This includes a theoretical study on1.3-&amp;#956m InGaAsP/InP multiple QW active regions, as wellas an experimental investigation of novel, highly strained1.2-&amp;#956m InGaAs/GaAs single QWs. Two high-accuracyabsolute reflectance measurement setups were built for thecharacterization of various DBRs. Reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs/GaAs DBRs than previously anticipated.Near-room temperature operation of a single-fused1.55-&amp;#956m VCL with an InP/InGaAsP bottom DBR wasobtained. A thermal analysis of this device structure clearlyindicated its limited capabilities in terms of high-temperatureoperation. As a result, further efforts were directed towardsall-epitaxial GaAs-based VCLs. Record-long emission wavelengthsto above 1260 nm were obtained from InGaAs VCLs based on anextensive gain–cavity detuning. These devices showed verypromising performance characteristics in terms of thresholdcurrent and light output power, indicating good potential forbeing a viable alternative to GaInNAs-based VCLs.

In this work, we have reported the design, MBE-growth and fabrication of strain-balanced n-type modulation-doped (MD) InGaAlAs/InGaAs multiple quantum wells laser/SOAs on InP. The quantum well contains a lattice-matched InGaAs core, a compressive-strained InGaAs padding, and a tensile-strained InGaAlAs spacer. Two kinds of samples having similar structure but different fundamental transition wavelength of 1.55 £gm and 1.48 £gm are separately prepared for investigating their characteristics in optical amplification under forward bias and electro-absorption under reversed bias. Also, the technique of growing high-quality InGaAlAs with solid-source molecular beam epitaxy has been established and the resulting InGaAlAs bulk and QWs samples are extensively characterized by double-crystal X-ray diffraction, transmission electron microscopy, electroluminescence, and photoluminescence measurements. For £f = 1.55 £gm samples, ridge-waveguide lasers of Fabry-Perot (FP) type and tilted-end-facet (TEF) type were fabricated by a new developed multi-step wet-etching process. When injection current density > 20A/cm^2, electroluminescence spectra show higher optical gain for the quantum well e1-hh2 transition at £f = 1460 nm than the e1-hh1 transition at £f = 1550 nm. The FP laser shows a lasing peak of £f = 1514 nm at threshold. Additional lasing wavelength at £f =1528 nm and 1545 nm were observed sequentially as the injection current increased. However, for the TEF laser, only the emission at £f = 1511 nm was observed. These TE-polarized lasing wavelengths are consistent with the £_-like absorption peaks in photocurrent spectra. The lasing performance is possible attributed to optical transitions within quantum dots/wires which are formed by the strain-field profile and alloy segregation/migration. For £f = 1.48 £gm samples, the differential absorption spectroscopy, which measures the change of transmission (£GT/T) in the presence of electric field, is used to study the electro-absorption modulation behavior of MD-SOA¡¦s. A sample with n-type modulation-doping amounting to a sheet density of 3.5 ¡Ñ 10^11 cm^-2 per QW and combining with a hole-stopping barrier represents the largest chirp parameter (£Gn/£Gk) under reversed bias, which offers an excellent platform to realize electro-refractive devices with larger refractive index changes (£Gn) but lower differential absorption (£G£\) near £f = 1.55 £gm, which is also our interested region of operation. In addition, we have succeeded in reducing the length of conventional constant-width multimode interference (MMI) coupler of K = 0.15 and 0.28 more than 32% by a novel stepped-width design concept. By extending the stepped-with idea, we show that it is possible to obtain 2x2 waveguide couplers with new power splitting ratios of 7%, 64%, 80% and 93% for cross coupling by cascading two short MMI sections. We further realize freely chosen power splitting ratio by interconnecting a pair of unequal-width waveguides as the phase-tuning section into the middle of two short MMI sections. These compact and low loss MMI-based devices use only rectangular geometry without any bent, curved, and tapered waveguides. They offer valuable new possibilities for designing waveguide-based photonic integrated circuits.

The objective of this work was to study the noise in semiconductors and relate the transport mechanisms in the devices with the noise from the devices. The main part of the work was to set up a system for the measurement of noise in semiconductor devices. To establish the sensitivity of the system, it was calibrated at different temperatures. Some of the results from GaAs pn-junction showed some anomaly from that available in the literature. But certain points are yet to be clarified. This requires certain developments in the measurement system. In the case of QWIPS structures, studies on some samples with varying number of wells are required and in order to study the GR noise spectra and other activated processes, we need to study the temperature dependence of the noise and a larger bias variation for studying the low frequency current noise.

<p>Vertical-cavity lasers (VCLs) are of great interest as lightsources for fiber-optic communication systems. Such deviceshave a number of advantages over traditional in-plane laserdiodes, including low power consumption, efficient fibercoupling, on-chip testability, as well as potential low-costfabrication and packaging. To date, GaAs-based VCLs operatingat 850 nm are the technology of choice for short-distance,high-speed data transmission over multimode fiber. Forlong-distance communication networks, long-wavelength (LW) VCLsoperating in the 1.3 and 1.55-&#956m transmission windowsof standard singlemode fibers are desired. However, despiteconsiderable worldwide development efforts, the commercialbreakthrough of such devices has still to be achieved. This ismainly due to shortcomings of the intrinsic material propertiesof InP-based material systems, traditionally employed in LWlaser diodes. While LW quantum well (QW) active regions basedon InP are well established, efficient distributed Braggreflectors (DBRs) are better built up in the AlGaAs/GaAsmaterial system. Therefore, earlier work on LW VCLs has focusedon hybrid techniques such as bonding between InP-based QWs andAlGaAs/GaAs DBRs using waferfusion. More recently, however, themain interest in this field has shifted towards all-epitaxialGaAs-based devices employing novel 1.3-&#956m activematerials with strained GaInNAs QWs as one of the mostpromising candidates.</p><p>The main focus of this thesis is on the characterization andanalysis of LW VCLs and building blocks thereof, based on bothInP and GaAs substrates. This includes a theoretical study on1.3-&#956m InGaAsP/InP multiple QW active regions, as wellas an experimental investigation of novel, highly strained1.2-&#956m InGaAs/GaAs single QWs. Two high-accuracyabsolute reflectance measurement setups were built for thecharacterization of various DBRs. Reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs/GaAs DBRs than previously anticipated.Near-room temperature operation of a single-fused1.55-&#956m VCL with an InP/InGaAsP bottom DBR wasobtained. A thermal analysis of this device structure clearlyindicated its limited capabilities in terms of high-temperatureoperation. As a result, further efforts were directed towardsall-epitaxial GaAs-based VCLs. Record-long emission wavelengthsto above 1260 nm were obtained from InGaAs VCLs based on anextensive gain–cavity detuning. These devices showed verypromising performance characteristics in terms of thresholdcurrent and light output power, indicating good potential forbeing a viable alternative to GaInNAs-based VCLs.</p>