MSc & PhD Thesis

    • Duplan, V., “CONCEPTION D’UN BIOCAPTEUR BASÉ SUR LA PHOTOLUMINESCENCE DU GAAS (001) POUR LA DÉTECTION DE MICRO-ORGANISMES“, MSc in Electrical Engineering, 2011, Université de Sherbrooke, Sherbrooke, Canada [pdf(fr)].

      Pendant que la menace potentielle du bioterrorisme augmente, il y a grand besoin d’un outil qui peut détecter les agents biologiques contaminants dans l’environnement de façon rapide, fiable et précise. Par contre, les méthodes traditionnelles utilisées nécessitent l’utilisation de laboratoires d’analyse sophistiquée, souvent dans des installations centralisées, ce qui demande un capital considérable et une main-d’œuvre hautement qualifiée. Les biocapteurs peuvent essentiellement servir en tant que dispositif à faible coût et très efficace à cet effet. De plus, ils peuvent être utilisés dans d’autres domaines, au jour le jour, tel pour la surveillance de contaminants dans les produits comestibles.
      Dans le but de résoudre ce problème, une nouvelle approche pour la fabrication d’un biocapteur optique a été développée. Celui-ci serait capable de détecter, de façon directe, des micro-organismes pathogénes qui seraient immobilisés à sa surface plus rapidement et plus aisément qu’avec les méthodes conventionnelles. En effet, les expériences présentées visent la fabrication d’un biocapteur suite à la déposition de molécules biochimiques sur une hétérostructure de GaAs/AlGaAs. Le biocapteur ainsi produit tire parti de l’émission de la photoluminescence émise par ce semi-conducteur quantique III-V pour la détection de micro-organismes immobilisés spécifiquement et négativement chargés.
      La présente recherche est basée sur des techniques novatrices de biocapteurs pour lesquelles il existe peu de littérature. Les travaux expérimentaux et les explications théoriques se révèlent ainsi de nature très exploratoires. Les résultats préliminaires obtenus ont d’ailleurs été similaires aux prédictions initiales. De plus, les détails théoriques et explications physiques permettent de comprendre l’origine des résultats obtenus et d’établir, de manière convaincante, les procédures à suivre pour une architecture optimale.

    • Marshall, G.M, “ELECTRO-OPTIC INVESTIGATION OF THE n-ALKANETHIOL GaAs(001) INTERFACE: SURFACE PHENOMENA AND APPLICATIONS TO PHOTOLUMINESCENCE-BASED BIOSENSING“, PhD in Electrical Engineering, 2011, Université de 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 practical interest are self-assembled monolayers (SAMs) comprised 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 terms of the requisite sensor chemistry and the passivation effect such coupling is known to afford. In this thesis, the SAM-GaAs interface is investigated in the context of a photonic biosensor based on photoluminescence (PL) variation. The scope of the work is categorized into three parts: i) the structural and compositional analysis of the surface using X-ray photoelectron spectroscopy (XPS), ii) the investigation of electronic properties at the interface under equilibrium conditions using infrared (IR) spectroscopy, the Kelvin probe method, and XPS, and iii) the analysis of the electro-optic response under steady-state photonic excitation, specifically, the surface photovoltage (SPV) and PL intensity.

      Using a partial overlayer model of angle-resolved XPS spectra in which the component assignments 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 theoretical surface morphologies. Modal analysis of transmission IR spectra show 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 the SAM.
      Lastly, the surface Fermi level position is determined by XPS and is used to interpret SPV results in terms of a thiol-induced reduction of the surface cross-section for minority carrier-capture. Numerical analysis confirms this result based on the carrier transport theory of PL intensity by means of a reduction of the surface recombination velocity.

    • Stanowski, R.W, “Nano-ingéniérie de bande interdite des semiconducteurs quantiques par recuit thermique rapide au laser“, PhD in Electrical Engineering, 2011, Université de Sherbrooke, Sherbrooke, Canada. [pdf]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/AlGaAs 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.

    • Carrier, D., SELF-REFERENCED SURFACE PLASMONS INTERFEROMETRY: A WAY TOWARDS BIOSENSING“, MSc in Electrical Engineering, 2010, Université de Sherbrooke, Sherbrooke, Canada. [pdf(fr)]
      Accessibility to advanced analysis techniques is often problematic when establishing diagnostics by medical personel. Classical techniques often require considerable infrastructures or needs large and hard-to-obtain instruments.
      To solve this problem, the usage of a technological platform composed of the partial integration of a biosensor upon a self-emitting structure is an interesting starting point. This platform address directly the technology accessibility problem by reducing the size and price of the technology. The usage 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.
      On the other hand, non-integrated systems are usually more flexible regarding the possible detection processes but are also more sensitive, using extensive and complex optical systems. The integration of an interferometric system and its linkage to the existing technological platform allows the implementation of a novel measurement technique, presenting both a phase shift measurement scheme and the conventional SPR shift measurement, leading to an increase in measurement accuracy and therefore sensitivity.
      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. [pdf(FR)]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.

  • Lepage, D., 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 presented is based on very innovative biosensing techniques, on which only very a small amount of literature exists. The experimental and theoretical works presented have therefore been very exploratory and the initial results even went against preliminary expectations. Nonetheless, theoretical details have been developed afterwards to describe the origin of the obtained results and allowed to establish, in a convincing manner, the procedure to follow for an optimal architecture. Critical parameters where identified and their inter-relations established through experimental results and a second round of theoretical analysis. Subsequently, final measurements showed a strong correlation with the latest theoretical model.