- Nazemi, E., “PHOTONIC MONITORING OF BIOLOGICAL ACTIVITIES OF BACTERIA IMMOBILIZED ON BIOFUNCTIONALIZED SURFACES OF QUANTUM SEMICONDUCTORS “, PhD in Electrical Engineering, 2017, Université de Sherbrooke. [ pdf. ]
Monitoring the viability, growth and cellular metabolism of bacteria can contribute significantly to the early diagnosis of disease, but can also help improve yield of bacterial products in industrial- or small-scale experiments. Conventional methods applied for investigation of antibiotic sensitivity of bacteria are mostly culture-based techniques that are time-consuming and take at least 12 h to reveal results. This delay leads to overtreatment of a wide range of infections with broad spectrum antibiotics which is costly and may lead to the development of resistance to these precious antibiotics, whereas rapid detection of a viral infection or absence of bacteria could prevent such treatments and, in the case of bacterial infection, identification of antibiotic susceptibility could allow use of narrow spectrum antibiotics. The project outlined in this document aims at monitoring biological activities of live bacteria immobilized on biofunctionalized surfaces of quantum semiconductor (QS) microstructures. The method takes advantage of the sensitivity of photoluminescence (PL) emitting semiconductors to the perturbation of the electric field induced by the electric charge of bacteria immobilized on the surface of these structures. Our hypothesis was that bacteria growing on the surface of biofunctionalized QS biochips would modify their PL in a different, and measurable way in comparison with inactivated bacteria. In the first phase of the project, we investigated an innovative method involving PL monitoring of the photocorrosion effect in GaAs/AlGaAs heterostructures. Maintaining the balance between device sensitivity and stability in the biosensing (aqueous) environment allowed us to detect Escherichia coli K12 in phosphate buffered saline solutions (PBS) at an attractive limit of detection of 103 CFU/mL in less than 2 hours. Following this research, we hypothesised that these heterostructures could be employed to develop a method for inexpensive and quasi-real time monitoring of the growth and antibiotic susceptibility of bacteria. One of the key elements in the development of this biosensing platform was to demonstrate that GaAs (001), normally used for capping PL emitting GaAs/AlGaAs heterostructures, would not inhibit the growth of bacteria. In the second phase of the project, we explored the capture and growth of E. coli K12 on bare and biofunctionalized surfaces of GaAs (001). It has been determined that the initial coverage, and the subsequent bacterial growth rates are dependent on the biofunctionalization architecture used to capture bacteria, with antibody biofunctionalized surfaces exhibiting significantly higher capture efficiencies. Moreover, for suspensions containing bacteria at less than 105 CFU/mL, it has been found that the surface of GaAs wafers could not support the growth of bacteria, regardless of the type of biofunctionalization architecture. In the third phase of the project, we used PL to monitor the growth and antibiotic susceptibility of E. coli K12 and E. coli HB101 bacteria. While immobilization of bacteria on the surface of GaAs/AlGaAs heterostructures retards the PL monitored photocorrosion, growth of these bacteria further amplifies this effect. By comparing the photocorrosion rate of QS wafers exposed to bacterial solutions with and without antibiotics, the sensitivity of bacteria to the specific antibiotic could be determined in less than 3 hours. Due to the small size, low cost and rapid response of the biosensor, the proposed approach has the potential of being applied in clinical diagnostic laboratories for quick monitoring of antibiotic susceptibility of different bacteria.
- Lacour, V., “OPTIMISATION D’UN MICROCAPTEUR GAAS A ONDES ACOUSTIQUES ET DE SA BIOINTERFACE POUR LA DETECTION DE PATHOGENES EN MILIEU LIQUIDE”, PhD in Electrical Engineering 2016, Thèse en cotutelle à l’Université de Franche-Comté et à l’Université de Sherbrooke. [ pdf (fr). ]
Les besoins croissants dans différents domaines et dans de nombreuses situations, de donner une information en temps réel sur la présence d‘un organisme biologique dans un environnement spécifique, ont motivé le développement d‘une multitude de technologies de détection. Ces technologies se regroupent sous le terme de « biocapteur », outil de mesure employé pour détecter des éléments biologiques dans les domaines de l‘agro- alimentaire, de l‘environnement, du biomédical et de la biosécurité. L‘industrialisation et le développement des échanges commerciaux alimentaires ont entraîné, ces dernières années, plusieurs crises sanitaires associées à une mauvaise gestion des produits de consommation (exemple : « crise du concombre » en France et en Allemagne en mai 2011) ou à un mauvais entretien des installations de conditionnement ou de traitement des eaux et/ou des aliments (exemple : crise de la légionellose à Québec au Canada en 2012). Ainsi, l‘utilisation de biocapteurs pour une détection rapide, sensible et sélective, d‘organismes pathogènes répond aux inquiétudes quant aux risques d‘infection pour la population. Ces raisons expliquent leur plein essor ces trente dernières années.Les performances et les caractéristiques d‘un biocapteur vont dépendre des technologies employées pour la capture de l‘élément biologique (biointerface) et la conversion de cet évènement en un signal mesurable (transducteur). Nous nous sommes focalisés sur l‘étude d‘un transducteur à ondes élastiques, celui-ci permettant d‘effectuer des analyses directes (sans l‘intervention de marqueurs) et en temps réel. Ils ont également l‘avantage d‘être facilement miniaturisables et peuvent être l‘objet d‘application portative. Historiquement, les premiers capteurs acoustiques utilisés sont les résonateurs à ondes élastiques de cisaillement dans le volume (TSM) dont la microbalance à quartz (QCM) est un exemple. Les premiers travaux sur le QCM ont été initiés par Sauerbrey en 1959. Dès lors, la structure, les matériaux employés et les procédés de fabrication pour les TSMs n‘ont eu de cesse d‘évoluer et de s‘élargir. Dans ce rapport, nous présentons un biocapteur à onde de cisaillement de volume conçu en arséniure de gallium (GaAs). Ce choix de matériau est motivé par plusieurs années de développement et d‘étude de celui-ci, au sein de notre groupe, pour des applications acoustiques. Les plus récents travaux de recherche dans ce domaine ont été conclus par la thèse d‘Alex Bienaimé intitulée « Microcapteur en arséniure de gallium pour la détection de molécules dans un fluide ». Ces travaux donnèrent de solides bases sur la modélisation, la fabrication, la fonctionnalisation et le test de ces dispositifs. Cependant, les premiers résultats sur ce biocapteur ont montré les limites dans l‘obtention des performances escomptées. Nous nous appuierons sur ces travaux et ces résultats pour développer des pistes d‘optimisation en termes de sensibilité et spécificité à travers l‘étude de nouvelles structures, géométries et procédés pour la biointerface et le transducteur. Dans le chapitre 1, nous énoncerons l‘état de l‘art des domaines explorés menant à la justification des choix sélectionnés pour la suite des travaux. Nous positionnerons, au préalable, le capteur étudié pour l‘application ciblée dans un contexte global et par rapport aux autres technologies existantes. Dans le chapitre 2, nous rappellerons les relations et modèles théoriques permettant de comprendre le fonctionnement du capteur et de prévoir, notamment via la simulation, les performances de celui-ci. Nous détaillerons également les techniques de fabrication employées au cours de ce travail pour l‘élaboration du transducteur et de sa cellule fluidique. Dans le chapitre 3, nous analyserons et caractériserons l‘interface de bio- reconnaissance utilisée pour la capture d‘éléments biologiques. Après une étude des techniques employées, nous effectuerons les caractérisations fines de l‘interface dans le but de comprendre les phénomènes à l‘interface GaAs-biomolécule. Enfin nous discuterons des améliorations possibles pour augmenter le nombre de sites de reconnaissance, et par conséquent, pour optimiser la sensibilité du capteur. Dans le chapitre 4, nous décrirons les procédés mis en oeuvre pour la régénération de la biointerface caractérisée précédemment, dans l‘objectif de réduire le coût global d‘utilisation du capteur. Nous prendrons soin de choisir des techniques permettant de préserver autant que possible la nature, le volume et la qualité du substrat régénéré afin qu‘il conserve les mêmes propriétés de transduction. Enfin dans le chapitre 5, nous donnerons les résultats de test du transducteur. Nous analyserons notamment les paramètres environnementaux pouvant influencer, de façon critique, les performances et la fiabilité du résonateur. Nous confronterons également les valeurs caractéristiques du dispositif réel avec les modèles étudiés dans le chapitre 2. L‘ensemble des analyses effectuées dans ce chapitre, nous permettra de conclure sur l‘efficacité d‘un tel capteur pour l‘application visée et de dégager les perspectives d‘optimisation.
- Béal, R., “LASER INDUCED QUANTUM WELL INTERMIXING: REPRODUCIBILITY STUDY AND FABRICATION OF SUPERLUMINESCENT DIODES”, PhD in Electrical Engineering, 2015, Université de Sherbrooke. [ pdf (fr). ]
Photonic Integrated Circuits (PIC) are of tremendous interest for photonics system in order to reduce their power consumption, size, fabrication cost and improve their reliability of fiber optics linked discrete component architecture. However, unlike for microelectronics, in photonics different heterostructures are required depending on the type of device (laser sources, detectors, modulators, passive waveguides…). Therefore photonics integration needs a technology able to produce multiple bandgap energy wafers with a suitable final material quality in a reproducible manner and at a competitive cost: a technological challenge that has not been completely solved yet. Quantum Well Intermixing (QWI) is a post growth bandgap tuning process based on the localized and controlled modification of quantum well composition profile that aims to address these matters. UV laser induced QWI (UV-Laser-QWI) relies on high power excimer laser to introduce point defects near the heterostructure surface. By adjusting the laser beam shape, position, fluence and the number of pulse delivered, the different regions to be intermixed can be defined prior to a rapid thermal annealing step that will activate the point defects diffusion across the heterostructure and generate quantum well intermixing. UV-LaserQWI presents the consequent advantage of allowing the patterning of multiple bandgap regions without relying on photolithographic means, thus offering potentially larger versatility and time efficiency than other QWI processes. UV-Laser-QWI reproducibility was studied by processing samples from an InGaAs/InGaAsP/InP 5 quantum well heterostructure emitting at 1.55 µm. 217 different sites on 12 samples were processed with various laser doses. The quantum well intermixing generated was then characterized by room temperature photoluminescence (PL) mapping. Under those experimental conditions, UV-Laser-QWI was able to deliver heterostructures with a PL peak wavelength blue shift controlled within a +/- 15 % range up to 101.5nm. The annealing temperature proved to be the most critical parameter as the PL peak wavelength in the laser irradiated areas varied at the rate of 1.8 nm per degree Celsius. When processing a single wafer, thus limiting the annealing temperature variations, the bandgap tuned regions proved to be deliverable within ± 7.9%, hence establishing the potential of UV-Laser-QWI as a reproducible bandgap tuning solution. The UV-Laser-QWI was used to produce multiple bandgap wafers for the fabrication of broad spectrum superluminescent diodes (SLD). Multiple bandgap energy profiles were tested and their influence on the SLDs’ performances was measured. The most favorable bandgap modifications for the delivery of a very broadband emitting SLD were analyzed, as well as the ones to be considered for producing devices with a flat top shaped spectrum. The intermixed SLDs spectra reached full width at half maximum values of 100 nm for a relatively flattop spectrum which compare favorably with the ≈ 40nm of reference devices at equal power. The light-intensity characteristics of intermixed material made devices were very close to the ones of reference SLD made from as-grown material which let us think that the alteration of material quality by the intermixing process was extremely limited. These results demonstrated that the suitability of UV-Laser-QWI for concrete application to photonic devices fabrication. Finally, an alternative laser QWI technique was evaluated for SLD fabrication and compared to the UV laser based one. IR-RTA relies on the simultaneous use of two IR laser to anneal local region of a wafer: a 980 nm laser diode coupled to a pigtailed fiber for the wafer background heating and a 500 µm large beam TEM 00 Nd:YAG laser emitting at 1064 nm to anneal up to intermixing temperature a localized region of the wafer. The processed samples exhibited a 33 % spectral width increase of the spectrum compare to reference device at equal power of 1.5 mW. However, the PL intensity was decreased by up to 60 % in the intermixed regions and the experiments proved the difficulty to avoid these material degradations of material quality with IR-RTA.
- Jimenez, A., “ UNE BIOCAPTEUR A BASE DE RESONANCE DE PLASMONS DE SURFACE INTÉGRÉ MONOLITHIQUEMENT AVEC UNE SOURCE D’EXCITATION”, PhD in Electrical Engineering, 2015, Université de Sherbrooke. [ pdf (en). ]
Le champ biomédical n’a pas échappé à l’évolution de la technologie, elle cherche aussi à intégrer plusieurs fonctions dans un espace restreint. Un des points forts du développement est la massification de points de service, afin d’obtenir un diagnostic rapide des maladies. Le diagnostique aux premières étapes de son évolution permettra réduire considérablement les coûts associés aux traitements des patients. Le présent document exprimera une alternative à l’évolution de la technologie des biocapteurs qui sont basés sur le phénomène optique appelé résonance par plasmons de surface. Ce projet de recherche vise l’étude de l’intégration monolithique des deux tiers des composants principaux qui conforment normalement à ce type de biocapteurs optiques. Tandis que d’autres projets de recherche ont centré leurs travaux sur l’intégration de la surface de réaction et le détecteur, notre travail a pris en compte l’intégration de la source de lumière et la surface de réaction biologique. Deux types de sources ont été employés au moment de faire la conception, l’étude de matériaux, la fabrication et la caractérisation de la performance de notre dispositif. La première source a employé des puits quantiques à l’intérieur d’une gaufre de GaAs qui nécessitait un pompage optique pour son fonctionnement. La deuxième source a eu une gaufre commerciale employée pour la fabrication des diodes d’émission lumineuse verticale, qui a dû être excitée par un courant électrique. On a découvert que les deux types de sources sont complémentaires. La source avec des puits quantiques a démontré une amélioration de la performance en comparaison à notre système commercial de référence. La deuxième source a démontré la faisabilité d’intégration monolithique en permettant se rapprocher à la fabrication d’un prototype commercial. La porte reste donc ouverte pour la poursuite du développement de cette technologie en cherchant un nouveau système employant ces deux sources, mais usant de meilleures caractéristiques.
- Liu, N., “ON THE ORIGIN OF UV LASER-INDUCED QUANTUM WELL INTERMIXING IN III-V SEMICONDUCTOR HETEROSTRUCTURES”, PhD in Electrical Engineering, 2013, Université de Sherbrooke. [ pdf (en). ].
The research project presented here aims to study the applicability of an integrated plasmonic sensor through semiconductor nanostructures with quantum and luminescent properties. The approach presented is global; that is, to answer fundamental questions involving the understanding of photonic phenomena, device development and fabrication, possible characterization methods, and the application of an integrated SPR transducer to biodetection . In other words: under what circumstances and how should an integrated plasmonic transducer be performed for application to the delocalized detection of pathogenic elements? In order to generate a simple instrument at the user level, the
Thus, monolithic plasmonic sensors are designed using theoretical models presented here. A conjugated hyperspectral measuring instrument for directly mapping the dispersion relationship of the diffracted plasmons was constructed and tested. This instrument is used to map diffusion elements. Finally, a demonstration of the operation of the device, applied to the biocharacterization of simple events, such as bovine serum albumin and the detection of a specific strain of influenza A. is delivered. This therefore answers the question of feasibility of a plasmonic nanosystem applicable to the detection of pathogens.
- Lepage, D., ” SEMICONDUCTOR DEVICES FOR PHOTONIC BIODETECTION AND HYPERSPECTRAL IMAGING “, PhD in Electrical Engineering, 2012, Université de Sherbrooke. [ pdf (en). ].
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 show 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.
Duplan, V., ”DESIGNING A BIOSENSOR BASED ON GAAS PHOTOLUMINESCENCE (001) FOR THE DETECTION OF MICROORGANISMS “, MSc in Electrical Engineering, 2011, University of Sherbrooke, Sherbrooke, Canada [ pdf (en) ].
As the potential threat of bioterrorism increases, there is a great need for a tool that can detect biological contaminants in the environment quickly, reliably and accurately.In contrast, the traditional methods used require the use of sophisticated analytical laboratories, often in centralized facilities, which requires considerable capital and a highly skilled workforce. Biosensors can essentially serve as a low cost and highly efficient device for this purpose. In addition, they can be used in other fields, day-to-day, such as for monitoring contaminants in edible products.
In order to solve this problem, a new approach for the fabrication of an optical biosensor has been developed. This one would be able to detect, in a direct way, pathogenic microorganisms which would be immobilized on its surface more quickly and more easily than with the conventional methods. Indeed, the experiments presented aim at the fabrication of a biosensor following the deposition of biochemical molecules on a GaAs / AlGaAs heterostructure. The biosensor thus produced takes advantage of the emission of photoluminescence emitted by this III-V quantum semiconductor for the detection of specifically immobilized and negatively charged microorganisms.
The present research is based on novel biosensor techniques for which there is little literature. Experimental work and theoretical explanations are thus very exploratory in nature. The preliminary results obtained were similar to the initial predictions. In addition, the theoretical details and physical explanations make it possible to understand the origin of the results obtained and to establish, in a convincing way, the procedures to follow for an optimal architecture.
Marshall, GM, ” ELECTRO-OPTICAL INVESTIGATION OF THE N-ALKANETHIOL GaAs (001) INTERFACE: PHENOMENA SURFACE AND APPLICATIONS TO PHOTOLUMINESCENCE-BASED BIOSENSING “, PhD in Electrical Engineering, 2011, University of Sherbrooke, Canada. [ pdf]
Semiconductor surfaces coupled to molecular structures derived from organic chemistry form the basis of an emerging class of field-effect devices.In addition to molecular electronics research, these interfaces are developed for a variety of sensor applications in the electronic and optical domains.Of self-assembled monolayers (SAMs) consisting of n-alkanethiols [HS (CH2) nR], which couple to the GaAs (001) surface through S-GaAs covalent bond formation.These SAMs offer potential functionality in the field of sensory chemistry and passivation.In this thesis, the SAM-GaAs interface is investigated in the context of a photonic biosensor-based photoluminescence (PL) variation. The scope of the work is categorized into three parts: Using a partial overlayer model of angle-resolved XPS spectra in which the component parts are shown to be quantitatively valid, the coverage fraction of methyl-terminated SAMs is shown to exceed 90%. Notable among the findings are a low-oxide, Ga-rich surface with elemental as present in sub-monolayer quantities consistent with surface morphology. Modal analysis of transmission IR spectra shows that the SAM molecular order is sufficient to support a Beer-Lambert determination of the IR optical constants, which yields the observation of a SAM-specific absorbance enhancement. By correlation of the IR absorbance with the SAM dipole layer potential, the enhancement mechanism is attributed to the vibrational moments added by the electronic polarizability in the static field of SAM.Lastly, the surface of the surface is determined by XPS and is used to interpret the surface cross-section for minority carrier-capture. Numerical analysis confirms this result based on the carrier theory of velocity recombination.
- Stanowski, RW, ” Nano-band Engineering of Quantum Semiconductors by Rapid Laser Thermal Annealing “, PhD in Electrical Engineering, 2011, University of Sherbrooke, Sherbrooke, Canada. [ pdf]
The ability to fabricate semiconductor wafers is a requirement for the production of monolithic photonic integrated circuits (PICs). The subject of the study has been proposed, the problem of achieving reproducible results has constantly challenged scientists and engineers. This issue is one of multiple sequential epitaxial growth and selective epitaxy, but also the standard quantum well intermixing (QWI) technique that has been investigated as a post-growth approach for bandgap engineering. Among different QWI techniques, those based on 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 wafer semiconductor comprising different quantum well (QW) or quantum dot (QD) microstructures. The accuracy of such an approach in the field of laser-induced temperature and temperature dependence of the laser-induced temperature, the dynamics of the heating-cooling process and the ability to take advantage of the diagnostics.In diagnosis. the frame of this thesis, I have investigated IR laser-induced QWI processes in QW wafers including GaAs / AlGaAs and InP / InGaAsP microstructures and in-grown QD microstructures grown on InP substrates. For this purpose, I have designed and set up a 2-laser system for selective rapid thermal annealing (Laser-RTA) of semiconductor wafers. The advantage of such an approach is that it allows for unattainable RTA techniques, while a tightly focused one of the IR lasers is used for “spot annealing”. These features have enabled me to introduce a new method for iterative bandgap engineering (IBESA) of semiconductor wafers. The method has 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 features of a QW wafer prepared for the manufacturing of a PIC. Also, this approach has the potential for tuning the emission wavelength of individual QDs in wafers designed, eg, for the manufacture of single photon emitters.
- ” SELF-REFERENCED SURFACE PLASMONS INTERFEROMETRY: A WAY TOWARDS BIOSENSING “, MSc in Electrical Engineering, 2010, University of Sherbrooke, Sherbrooke, Canada. [ pdf (en)]
Accessibility to advanced analysis techniques is often problematic when establishing diagnostics by medical personnel. Classical techniques often require considerable infrastructure or needs large and hard-to-obtain instruments.To solve this problem, the use of a biosensor approach to a self-emitting structure is an interesting starting point. This platform addresses the technology accessibility problem and reduces the size of the technology. The use of a structure compatible with microfabrication techniques widely used in microelectronics industry leaves the way to the possibility of upscaling production easily and with minimal costs.The other hand, non-integrated systems are generally more flexible than the possible detection processes. The integration of an interferometric system and its linkage to the existing technical platform allows the implementation of a technical measurement, presenting both a phase shift measurement scheme and the standard measurement technique.Using the Electromagnetic Theory of Coupled Modes within laminar structures to create the theoretical background and FEM (Finite element method) modelization to provide preliminary demonstrations, the objective of this project is to study the characteristics of a SPR (surface plasmon resonance) biosensor where the surficial refractive index change is measured with an interferometric approach. To do so, a microstructure is added to the biosensor surface in order to couple incident light to the plasmon surface modes.Those surface modes are resulting from the interaction and interference of the diffracted surface plasmons by the different microstructure components. In the case of a simple microstructure (e.g. a pair of finite adjacent gratings), the detailed analysis of the diffracted plasmons’ interaction is possible and demonstrated. This interaction is then linked to the inherent resonance shape of the microstructure and compared to other simple cases, like the classical SPR structure.This transformation of the sensor’s resonance shape increases the global precision achievable by the biosensor without greatly increasing its complexity. The interferometric method proposed here promise very interesting results under certain conditions, also defined and highlighted.
Genest, J., “QUANTUM WELL INTERMIXING CONTROLLED BY EXCIMER LASER FOR PHOTONIC DEVICE INTEGRATION“, PhD in Electrical Engineering, 2008, Université de Sherbrooke, Sherbrooke. Canada. [pdf]
Integration of discrete components into a single system, such as an electronic chip,increases the system total performance; makes new functionalities appear and lowers the overallmanufacturing cost. In microelectronics, theses important improvements have been largelyresponsible for enabling the recent advancements in information and communicationtechnologies. Because the fabrication of photonic integrated circuits requires the integration ofmultiple bandgap structures within a single semiconductor chip, their integration level is far fromthe one achieved in a common microprocessor chip.Among the potential techniques to achieve monolithic photonic integrated circuitspostgrowth quantum well intermixing in selected areas locally increases the effective band gapenergy of a semiconductor heterostructures. The thermally activated intermixing process isaccelerated by the diffusion of impurities and of point defects such as vacancies and interstitials.For this thesis work, we hypothesised that UV laser irradiation modulates point defect diffusionand generation in GaAs and InP based heterostructures and therefore controls quantum wellintermixing in specific areas.
This was verified by patterning GaAs and InP quantum well heterostructures with KrFand ArF laser pulses in various gaseous environments at different fluences and number of pulses.The intermixing was then activated during a rapid thermal annealing step. We demonstrated that in GaAs based heterostructure, excimer laser irradiation inhibitsquantum well intermixing by growing a surface stressor which prevents the diffusion of pointdefects toward the well. We highlighted the influence of physiorbed water vapour on the stressorgrowth and determined the spatial resolution of the technique. In InP based heterostructure, evenbelow ablation threshold, UV laser absorption in InP favours desorption of surface atoms whichgenerates an extra concentration of point defects. During the annealing, these point defectsparticipate to the intermixing process under the irradiated areas.
Dion, J., “MICROMACHINING OF PHOTOSENSITIVE GLASS WITH AN ARF EXCIMER LASER”, MSc in Electrical Engineering, 2008, Université de Sherbrooke, Sherbrooke, Canada. [pdf]
Glass is a technologically important material finding numerous applications in photonicsand optoelectronics. In the recent decade, we have also observed a growing interest inexploring the potential of this material for the manufacture of micro-electro-mechanicalsystems (MEMS). Conventional methods for micromachining of glass are prohibitivelyslow, and laser ablation leads to macrocracks and rough surfaces morphologies. In thatcontext, photosensitive glass ceramics, such as FoturanTM, offer significant advantages infabrication of commercial grade, optically transparent, two- and three-dimensional (2Dand 3D) microstructures. To address the problem of rapid fabrication of such microstructureswith smooth surface morphology, we have undertaken a study of micromachiningof FoturanTM with an ArF excimer laser (λ = 193nm) mask projection system. To ourknowledge, this is the shortest wavelength laser ever used for processing of FoturanTM.The applied micromachining technique consists of three major steps: 1) Irradiationwith the laser, 2) High-temperature annealing and, 3)Wet etching to remove the irradiatedand annealed glass volume. Due to the strong optical absorption at 193 nm, it wasexpected that a better control could be achieved of the machined surface morphologywhen compared to the previously reported results obtained with 266 and 355 nm lasers,or with femtosecond lasers. At the same time, the application of the excimer laser maskprojection should allow processing of relatively large dimension wafers.We have demonstrated that a one-step irradiation approach allows fabricating craterswith the maximum depth not exceeding 35 μm. Deeper craters, up to 120 μm, have beenfabricated following a series of irradiation-annealing-etching steps. We have fabricated aseries of complex 3D microstructures using special masks and a mask scanning technique.The amplitude of the surface roughness of as-fabricated microstructures was, typically,not worse than 100 nm. This is expected to be reduced to less than 10 nm by implementingpost-processing annealing. The results of this study have indicated clearly thefeasibility of the 193 nm excimer laser and the mask projection technique for rapid fabricationof 3D microstructures in photosensitive glass. The proposed method is expectedto find applications in the fabrication of, e.g., shallow microfluidic devices, or a specialtyof optoelectronic devices.
- Shaffer, E., “
EXCIMER LASER-INDUCED CRYSTALLIZATION OF AMORPHOUS CdSe THIN FILMS”, MSc
- in Electrical Engineering, 2007, Université de Sherbrooke, Sherbrooke, Canada. [
- Semiconductor nanocrystals, more specifically quantum dots (QDs), find many and more applications in photonics and, more recently, in the rapidly growing field of biodiagnostics. Research on colloidal QDs for biomedical imagery and biodetection already occupies a very important part of QDs literature. However, due to their instability outside of the solution and the requirement of special passivation procedures, colloidal QDs pose numerous problems in biodiagnostics and they are not well-suited for device integration. Other alternatives are being studied, that are compatible with microfabrication processes and that would allow for laser-induced modification (tuning) of QDs’ surface chemistry and their physical properties by using such techniques as laser irradiation. Two-dimensional (2D) arrays of epitaxial QDs have been proposed as a promising platform for biosensing. Another solution lies in laser-induced crystallization of amorphous thin films of semiconductors or, more precisely CdSe. Excimer laser crystallization technology is already widely used, especially in the thin-films transistors (TFT) industry and is therefore entirely compatible with microfabrication processes. Actually, this technique is used to crystallized amorphous thin films of silicon and its possible application to crystallize II-VI semiconductors has yet to be demonstrated. In this work, we demonstrate that ArF (193 nm) excimer laser irradiation can successfully lead to crystallization of amorphous, 85 nm thick, films of CdSe. We show that the crystallization can be monitored during the irradiation process by a related photoluminescence (PL) emission from the irradiated films. In addition to PL measurements, our films have been characterized by Raman spectroscopy and scanning electron microscopy (SEM). Our SEM images revealed the formation of CdSe nanorods and nanobeads. The presence of such small structures makes us to believe that quantum confinement could be achieved. We demonstrate that the ArF crystallization process is compatible with the integrated circuits fabrication techniques and it allows patterning to obtain photo-luminescent regions defined by the projection mask used in our homogenized beam delivery system. Size-controlled nanobeads or quantum dots could be the key to multiple wavelength-emitting II-VI photonic integrated circuits or biosensing devices.
- “STUDIES ON GOLD-SEMICONDUCTOR ARCHITECTURES FOR SURFACE PLASMON ASSISTED PHOTOLUMINESCENCE“, MSc in Electrical Engineering, 2006, Université de Sherbrooke, Sherbrooke, Canada. [pdf]
Surface plasmons polaritons on metal-semiconductor architecture can play a significant role in nanobiodetection. Those surface plasmons properties are particularly ideal for surface sensing. The general idea of the project is the conception of a biodetector, which probing mechanism is the resonance of surface plasmon polaritons (SPs) with light emitted by the semiconductor substrate via photoluminescence (PL). The measured signal is surface plasmon assisted PL, modulated by presence of biomolecules in the vicinity of the gold film. In addition, surface chemistry of the gold-thiol interface is utilized prior to biofunctionalization, allowing a selective design for the ultra-sensitive detection of different biomolecules. The presented architectures promise strong selectivity, through surface functionalization and enhanced sensivity, from SPs based measurements. The devices fabrication processes are kept simple to offer the benefits of integrated microstructures: miniaturisation, mass fabrication, easy operation and self-alignment between the source and the sensing element. The proposed architectures have open active regions in order to allow a continuous probing and, in addition to be self-referential systems, offer the potential for parallelism, allowing high-throughput screening.Experiments implied the fabrication of subwavelength gold gratings, within an architecture built on a GaAs/AlGaAs heterostructure substrate. Efficient architectures for the integrated infrared SP-PL coupling were designed, built, characterised and their properties analysed to achieve an extensive understanding of the physical processes implied in these integrated biosensors.The research hereby is based on the most recent technical biosensing, on which only a small amount of literature exists. The experimental and theoretical works presented the first exploratory results and the first results. Nonetheless, the following is a description of the results of this study, which is presented in the following table: Critical parameters where identified and their inter-relationships established through experimental results and a second round of theoretical analysis. Subsequently, final measurements showed a strong correlation with the latest theoretical model.