L'énergie solaire est une source d'énergie renouvenable, peu polluante, disponible universellement et abondante. Elle est donc une solution de choix pour résoudre les problèmes énergétiques et environnementaux de l'humanité. Cependant, les panneaux solaires couramment utilisés pour transformer l'énergie solaire en électricité sont encore trop dispendieux pour une utilisation répandue. L'utilisation de lumière concentrée se veut une méthode de réduire les coûts de l'électricité produite, mais cette réduction n'est pas encore atteinte. Ce projet propose d'explorer des matériaux et des structures semiconductrices fabriqués par épitaxie par jets chimiques qui pourraient être utilisés dans des cellules solaires optimisées pour la très haute concentration. En premier lieu, plusieurs designs de cellules solaires sont simulés avec une approche multiphysique pour identifier des structures permettant de minimiser les coûts de l'électricité à travers une maximisation du facteur de concentration. Basé sur ces structures de cellules solaires, plusieurs designs de jonctions tunnels sont simulés et une jonction tunnel standard (GaAs:Te/AlGaAs:C) est choisie. Le GaAs dopé au Te présente un problème de morphologie de surface à haut dopage. Ce problème est étudié et éliminé à travers l'optimisation des conditions de croissance. Dans le cas de l'AlGaAs dopé au C, le niveau de dopage est maximisé à travers l'utilisation d'un précurseur chimique qui n'est pas utilisé en CBE, le TMA. Suite à l'optimisation de ces deux matériaux, des jonctions tunnels avec d'excellentes performances sont crûes. Par la suite, une tentative de croissance de jonction tunnel GaInP/AlGaAs avec des boîtes quantiques en InAs permet d'améliorer le courant tunnel par rapport à une jonction tunnel sans boîtes, mais sans atteindre des performances satisfaisantes pour l'inclusion dans une cellule solaire. Ensuite, un matériau alternatif pouvant servir de jonction p-n dans les structures de cellules solaires, le GaInAsP, est caractérisé par photoluminescence pour explorer l'effet des paramètres de croissance sur la séparation de phase et l'influence de cette séparation sur les propriétés du matériau. On en découvre qu'une forte séparation de phase induit la présence d'états localisés sous le bandgap qui affecterait les performances d'une cellule solaire. Ensuite, il est démontré que le dopage de type n idéal est le Te alors que celui de type p est au Zn. Cependant, les temps de vie obtenus pour le GaInAsP dopé n ou p sont très bas et donneraient de mauvaises performances de cellules solaires. Ces temps de vie sont néamoins meilleurs que ceux obtenus pour l'AlGaAs, l'alternative au GaInAsP.

Cette thèse décrit l’incorporation de fer dans l’hétérostructure InGaAsP/InP par implantation ionique à haute énergie (MeV) suivi d’un recuit thermique rapide. L’alliage quaternaire InGaAsP est tout indiqué pour fabriquer des couches photoconductrices qui peuvent absorber dans le proche-infrarouge, à 1.3 µm ou 1.55 µm. Ce procédé vise à développer de nouveaux matériaux de forte résistivité pour l’holographie photoréfractive et la spectroscopie térahertz pulsée. À notre connaissance, cette investigation représente les premiers essais détaillés de l’implantation de fer dans le matériau InGaAsP/InP. Les principaux paramètres de fabrication, tels la fluence d’ions de fer, la température d’implantation et la température de recuit ont été explorés. Les propriétés physiques des matériaux produits ont été étudiées avec des mesures électriques (résistivité et effet Hall avec l’analyse de Van der Pauw), optiques (photoluminescence, absorption et réflectivité différentielle résolue en temps) et structurales (diffraction de rayons X, canalisation de la rétrodiffusion Rutherford et microscopie électronique en transmission). Pour fabriquer des couches à forte résistivité pour des applications holographiques à 1.3 µm, nos résultats ont montré qu’il est préférable d’éviter l’amorce de l’amorphisation lors de l’implantation du quaternaire pour maintenir une bonne qualité cristalline après recuit. Ceci favoriserait une compensation par l’activation du fer comme impureté profonde. Une résistivité de l’ordre de 10[indice supérieur 4] Ωcm est mesurée après recuit. Pour fabriquer des couches à forte résistivité pour des applications de spectroscopie térahertz pulsée à 1.55 µm, nous privilégions l’amorphisation par implantation froide et la recristallisation, ce qui réduit le temps de recombinaison des photoporteurs sous la picoseconde. L’émission d’ondes térahertz par ce matériau est démontrée sur une largeur de bande de 2 THz. L’évidence expérimentale montre la formation d’une microstructure polycrystalline dans la couche d’InGaAsP, ayant une forte densité de fautes planaires et une taille de grains nanométrique qui varient avec la température de recuit, ce qui suggère une connexion avec les propriétés optoélectroniques du matériau.

This thesis reports on an extensive investigation into the intrinsic frequency response of various MQW lasers as determined from parasitic-free relative intensity noise (RIN) measurements. Eleven structures were designed, grown and fabricated at Nortel Technology's Advanced Technology Laboratory in Ottawa. Five of the laser structures had active regions containing 10 QWs. The barrier layer composition for these structures was varied such that the emission wavelength corresponding to the barrier band-gap increased from 1.0 pm to 1.2 pm in 0.05 pm steps. The remaining six structures had a constant barrier layer emission wavelength of 1.1 pm but the number of quantum wells was varied from 5, 7, 8 to 14 in 2 well steps. In all structures the QWs were embedded in a graded- index-separate-confinement-heterostructure waveguiding region and were strained to 1.0 percent in compression. The devices processed from these structures were Fabry-Perot type lasers having cavity lengths ranging from 254 pm to 1016 pm. Resonance frequency and damping values as a function of injection current and single facet optical power, as well as optical spectra just below threshold, were obtained for over one hundred devices. From this data the response coefficient D, K factor, group velocity (vg), photon energy (hv), mirror loss (am), and internal absorption (aint) were characterized. Using these characterized parameters dg/dN, dg/ds, and the maximum theoretical intrinsic 3 dB bandwidth (fmax) were calculated. The effects of varying QW number, barrier height, and cavity length on all these parameters was investigated. Limitations with using the single mode rate equation model for these characterizations is discussed. As well, potential limitations with the basic design of the structures studied in this thesis as revealed by the results are explored. / Thesis / Candidate in Philosophy

The effect of strain (stress) on the below threshold output of InGaAsP diode lasers has been investigated theoretically and experimentally. The degree of polarization (DOP) and the polarization- resolved spectral output (PRSO) were obtained as a function of the external stress applied to the device. A correlation between the DOP and the peak of the PRSO as a function of the stress was found. This correlation suggests that below threshold, DOP can be used to measure the strain in the active region of lasers. A model based on a strain modified Shockley matrix for the band calculation and a strain modified dipole moment for the optical emission has been constructed to bridge the correlation between the DOP and PRSO. / Thesis / Master of Engineering (ME)

Le travail présenté dans cette thèse porte sur la conception, la fabrication et la caractérisation de sources prévues pour fonctionner à la fois comme diode laser et comme oscillateur paramétrique optique. Ces lasers sont conçus pour émettre sur un mode d’ordre supérieur afin de permettre une conversion de fréquence paramétrique avec les modes fondamentaux du guide à la fréquence moitié. La diode laser et l’OPO partagent la même cavité optique ; pour assurer l’accord de phase et corriger les écarts à la structure nominale induits lors de l’élaboration par épitaxie, la largeur de ruban est utilisée comme paramètre de contrôle des indices efficaces. Les diodes proposées sont donc étroites (3-5 µm) et gravées profondément. En conséquence, il est potentiellement intéressant d’utiliser des boîtes quantiques pour limiter les recombinaisons non radiatives sur les flancs. Dans le cadre de ce travail, nous avons conçu des diodes basées sur ce principe pour les deux systèmes GaAs/AlGaAs et InGaAsP/InP, qui permettent respectivement d’obtenir potentiellement une émission OPO au voisinage de 2 µm ou de 3 µm. Dans le cas de l’InGaAsP/InP, nous avons étudié au préalable l’indice de réfraction des alliages InGaAsP dans une plage de longueur d’onde jusque-là non couverte par la littérature. Ces données ont été acquises via des mesures d’indice efficace (m-lines) de couches guidantes d’InGaAsP épitaxiées en accord de maille sur un substrat d’InP. Pour des structures laser-OPO optimisées, les simulations montrent que le seuil OPO devrait être obtenu pour une puissance de pompe intracavité de quelques centaines de mW, qu’il est réaliste d’atteindre pour des diodes laser à l’état de l’art. Nous avons étudié les propriétés électro-optiques de diodes lasers à puits quantiques GaAs/AlGaAs réalisées sur la base de nos dessins; l’observation de l’effet laser sur le mode TE2 valide le dessin vertical original de nos diodes lasers. En vue de la fabrication de laser-OPO à ruban étroit, nous avons développé des procédés de fabrication nouveaux sur la Plateforme Technologique Amont (CEA – Grenoble), notamment la gravure profonde (>10 µm) par ICP-RIE. Enfin, nous avons proposé un concept alternatif de diode-OPO, comprenant des cavités laser et OPO distinctes couplées par un taper adiabatique / The work presented in this thesis deals with the design, fabrication and characterization of sources intended to function as both laser diodes and optical parametric oscillators. These lasers are designed to emit on a higher order mode to allow parametric frequency conversion with fundamental modes of the guide at half frequency. The laser diode and OPO share the same optical cavity; to ensure phase matching and correct nominal structure deviations induced during epitaxial processing, the ridge width is used as a control parameter of the effective indices. The proposed diodes are therefore narrow (3-5 μm) and etched deeply. Consequently, it is potentially interesting to use quantum dots to limit non-radiative recombination on the sidewalls. In the context of this work, we have designed diodes based on this principle for the two GaAs/AlGaAs and InGaAsP/InP systems, which respectively allow to potentially obtain an OPO emission in the vicinity of 2 μm or 3 μm. In the case of InGaAsP/InP, we previously studied the refractive index of InGaAsP alloys in a wavelength range not covered by literature to this day. This data was acquired via effective m-line index measurements of InGaAsP guiding layers epitaxially grown on and lattice-matched to an InP substrate. For optimized laser-OPO structures, simulations show that the OPO threshold should be obtained for an intracavity pump power of a few hundred mW, which is realistic to achieve for state-of-the-art laser diodes. We have studied the electro-optical properties of GaAs/AlGaAs quantum well laser diodes made on the basis of our designs; the observation of the laser effect on the TE2 mode validates the original vertical design of our laser diodes. For the manufacture of narrow-ridge lasers-OPOs, we have developed new manufacturing processes on the Plateforme Technologique Amont (Upstream Technology Platform, CEA - Grenoble), including deep etching (> 10 μm) by ICP-RIE. Finally, we have proposed an alternative diode-OPO concept, comprising distinct laser and OPO cavities coupled by an adiabatic taper

A detailed characterization of the Ini-xGaxAsyP1-j, quaternary material system lattice matched to GaAs, grown by gas source Molecular Beam Epitixy (MBE) has been performed. Photoluminescence, X-ray diffraction and Transmission Electron Microscopy (TEM) were used to study the lateral composition modulation (LCM) which was observed in this material system. Optimization of the growth process and the substrate orientation resulted in a significant reduction of the LCM. Additionally, a comprehensive analysis of the optical constants was performed which resulted in the first publication of wavelength and composition dependent index of refraction data for this material system. The combination of growth optimization and index of refraction data lead to the demonstration of efficient, low threshold operation of InGaAsP/GaAs based multiple quantum well lasers. In order to efficiently couple the above laser diodes to an external cavity to facilitate the generation of ultrashort pulses, antireflection facet coatings were required. As such, optical interference filters have been fabricated using a plasma enhanced chemical vapor deposition system, based on the SiOxNy material system. High quality antireflection facet coatings, suitable for application to the InGaAsP/GaAs diode lasers have been designed and fabricated, resulting in modal reflectivities of 1-2 x 10-4. Finally, an ultrashort-pulse external-cavity diode laser system was designed and manufactured which allowed the laser diode to be wavelength tuned and emit mode-locked ultrashort optical pulses. Pulses with sub 2 ps duration and greater than 1 mW average output power have been achieved. A study of the novel application of an asymmetric quantum well structure to the generation of ultrashort optical pulses has been proposed and initiated. / Thesis / Doctor of Philosophy (PhD)

III-V semiconductors are compounds made of elements from groups III and V of the periodic table. Most of these materials exhibit a direct bandgap, which makes them suitable for light emission and detection. Furthermore, ternary and quaternary III-V semiconductors offer some freedom in adjusting their material compositions, which also allows one to modify their bandgap energies, refractive indices, and other optical properties. This quality makes such materials suitable for the monolithic integration of laser sources with passive optical devices and detectors on a single chip. For example, such integration is used in indium phosphide (InP) technology for large-scale photonic integration in optical communication networks. Commercial integrated photonic circuits' functionality can be augmented by the implementation of nonlinear optical devices, enabling all-optical signal processing, frequency conversion, and on-chip sources of quantum light. This doctoral thesis focuses on design, fabrication, and testing of passive optical components based on III-V semiconductors. We explored various fabrication approaches for III-V nonlinear photonic devices. Among the III-V semiconductor platforms used in nonlinear photonics, we focused on AlGaAs as the most studied nonlinear optical platform, and InP and its quaternary derivatives as the most commercially developed platform. The fabrication processes for III-V photonic devices usually require the deposition of silica and chromium layers, and then three etch steps to etch the chromium, silica, and, finally, the III-V layer. In the thesis, we demonstrate a process which allows one to eliminate the chromium deposition and the associated etch step, thereby reducing the process complexity. We implemented this newly developed hard-mask process for etching numerous AlGaAs and InP photonic devices. This work was not only an important contribution to the University of Ottawa's cleanroom facility. The shared recipe can be used to recreate etch recipes for silica using soft masks like ZEP520a, PMMA, etc., at other similar university and research facilities around the world. The silica mask created using this process was later used to fabricate InP/InGaAsP-based half-core-etched and nanowire waveguides, which were used to perform the first reliable measurement of the nonlinear refractive index coefficient n₂ of InGaAsP/InP waveguides. We explored improved fabrication processes for AlGaAs waveguides, photonic crystals, and ring resonators. InP-based integrated optical devices are relatively difficult to fabricate because the etch byproducts are only volatile at elevated temperatures. Using a silica mask, we developed a very smooth etching process for InP waveguides with aspect ratios greater than 1:10. Suspended waveguide structures, where the guiding layer is surrounded by the air, are of great interest as they can exhibit large refractive index contrast for superior compactness and for achieving high intensity at low optical powers. We demonstrated fabrication process flows for creating suspended air-bridge structures in a 500-nm AlGaAs slab, which can be used in mid-IR sensing applications. The processes developed as part of this project cover a wide range of AlGaAs passive photonic devices such as waveguides, photonic crystals and ring resonators. Additionally, we demonstrated plasma etching selectivity improvements for AlGaAs etching using only a soft ZEP mask and were able to achieve a selectivity of 1:2.9. All these developments can be beneficial to other researchers working on III-V photonic devices. We also completed the first theoretical study of third-harmonic generation in dispersion-engineered AlGaAs suspended photonic crystal waveguide. Most importantly, we introduced a reliable and efficient method for modelling higher-order modes in photonic crystal waveguides that is less computationally intensive and far more accurate compared to the 3D FDTD method. We also experimentally demonstrate guided modes lying above the light line in AlGaAs photonic crystal waveguides. In one of the addition projects, we experimentally demonstrate third-harmonic generation (THG) in Silicon Nitride waveguides. In summary, this thesis presents details of the design and testing of different passive nonlinear III-V semiconductor photonic devices. In addition, this thesis presents the fabrication processes which can be used to reliably and repeatably fabricate photonic devices in these materials.

This work describes multiband photon detection techniques based on novel semiconductor device concepts and detector designs with simultaneous detection of dierent wavelength radiation such as UV and IR. One aim of this investigation is to examine UV and IR detection concepts with a view to resolve some of the issues of existing IR detectors such as high dark current, non uniformity, and low operating temperature and to avoid having additional optical components such as filters in multiband detection. Structures were fabricated to demonstrate the UV and IR detection concepts and determine detector parameters: (i) UV/IR detection based on GaN/AlGaN heterostructures, (ii) Optical characterization of p-type InP thin films were carried out with the idea of developing InP based detectors, (iii) Intervalence band transitions in InGaAsP/InP heterojunction interfacial workfunction internal photoemission (HEIWIP) detectors. Device concepts, detector structures, and experimental results are discussed. In order to reduce reflection, TiO2 and SiO2 nanostructured thin film characterization and application of these as anti-reflection coatings on above mentioned detectors is also discussed.

<p>Metamorphic buffer (MB) layers were studied as a means to grow epilayers on top of a GaAs substrate which have different lattice constant than the GaAs. Growths were done by molecular beam epitaxy on a GaAs (001) substrate. The growths of step-graded InGaAs and InGaAsP MBs have been investigated using both linear and logarithmic grading profiles. The logarithmic grading profile shows slight improvement in the crystal quality over the linear grading profiles. This is an indication that instead of increasing the strain with the same grading rate, it may be helpful to have higher grading rate at the beginning and lower grading rate at the end of the buffer. InGaAsP graded buffers were grown where group III ratio was kept fixed. However due to the existence of phase separation and lower relaxation the quaternary growths exhibited no performance improvement as might have been expected from growths with only group V grading. Also, the effects of using an InGaP layer grown at low temperature before the MB were determined. Quantum wells (QW), which were grown on top of the MBs, were used to probe the optical emission properties. No significant difference was observed in photoluminescence between the samples with a low temperature layer and without a low temperature layer. Annealing enhanced the PL intensity but the crystal quality degraded due to the appearance of surface defects. Surface undulations, known as “cross-hatch” (CH), were observed in the top MB layers. Atomic force microscopy (AFM) was used to analyze the surface morphology and degree of polarization (DOP) measurement was used to analyze the strain features in the final MB layer. Similar patterns of both surface morphology and strain field indicate a correlation between these two. From analysis of the periodicity of strain field and the CH, evidence was found in the support of one of the existing models of CH evolution which implies that the CH appears before the formation of MDs and subsequently MDs form at some troughs in the undulation.</p> / Master of Applied Science (MASc)