Au cours de ce travail, nous nous sommes intéressés à l'élaboration de cristaux photoniques colloïdaux d'architecture contrôlée afin d'étudier leur effet sur les spectres de photoluminescence de luminophores. Notre stratégie a été d'incorporer les émetteurs au sein des particules de silice composant les cristaux colloïdaux de façon à les répartir de manière homogène dans l'ensemble des matériaux. Nous présentons la synthèse des précurseurs minéraux et l'élaboration de cristaux colloïdaux d'épaisseur contrôlée à la couche près grâce à la technique de Langmuir-Blodgett. Ces structures sont caractérisées par une bande interdite qui affecte la propagation de la lumière. L'insertion d'une couche de particules de diamètre différent dans un cristal colloïdal induit l'apparition d'une bande passante au sein de la bande interdite. Nous avons ainsi étudié l'influence de la structure de cristaux avec et sans défaut(s) sur les spectres d'émission de différents luminophores. Nous avons observé une inhibition et une exaltation locale de la lumière émise dans les zones spectrales correspondant respectivement aux bandes stoppante et passante. Nous avons également observé des modifications réversibles des spectres de photoluminescence des émetteurs, lorsque ceux-ci sont incorporés au sein de cristaux colloïdaux dont les propriétés optiques peuvent être modulées via l'application d'un stimulus extérieur.

Semiconductor nanowires are nanostructures with lengths up to few microns and small cross sections (10ths of nanometers). In the recent years the development in the field of III-N nanowire technology has been spectacular. In particular they are consider as promising building in nanoscale electronics and optoelectronics devices; such as photodetectors, transistors, biosensors, light source, solar cells, etc. In this work, we present fabrication and the characterization of photodetector and light emitter based devices on III-N nanowires. First we present a study of a visible blind photodetector based on p-i-n GaN nanowires ensembles grown on Si (111). We show that these devices exhibit a high responsivity exceeding that of thin film counterparts. We also demonstrate UV photodetectors based on single nanowires containing GaN/AlN multi-axial quantum discs in the intrinsic region of the nanowires. Photoluminescence and cathodoluminescence spectroscopy show spectral contributions above and below the GaN bandgap according to the variation of the discs thickness. The photocurrent spectra show a sub-band-gap peak related to the interband absorption between the confined states in the large Qdiscs. Finally we present a study of photodetectors and light emitters based on radial InGaN/GaN MQW embedded in GaN wires. The wires used as photodetectors showed a contribution below the GaN bandgap. OBIC measurements demonstrate that, this signal is exclusively generated in the InGaN MQW region. We showed that LEDs based on this structure show a electroluminescence emission and a red shift when the In content present in the QWs increases which is in good agreement with photoluminescence and cathodoluminescence results.

L'insertion de nombreuses impuretés magnétiques dans des matériaux semiconducteurs massifs permet d'obtenir un comportement ferromagnétique. D'autre part, les boîtes quantiques confinent les porteurs dans les trois dimensions, permettant un contrôle individuel de chacun. Le travail présenté ici concerne l'insertion d'une unique impureté magnétique (Manganèse) dans une seule boîte quantique de semiconducteur II-VI. Cet objet permet l'étude directe, par des moyens expérimentaux relativement simples, de l'interaction entre l'impureté magnétique et un porteur confiné dans la boîte quantique. De manière uniquement optique, le spin de l'impureté peut être contrôlé et détecté. Cela en fait un candidat possible pour réaliser un codage quantique de l'information.<br />La réalisation de ces échantillons, en épitaxie par jets moléculaires, est d'abord détaillée. La ségrégation du Mn au cours de la croissance est utilisée pour réduire la densité d'atomes Mn tout en la contrôlant. Des expériences de micro-spectroscopie optique permettent de valider cette méthode. Ensuite, une étude fine de l'interaction impureté-porteur est réalisée. Les spectres expérimentaux sont analysés à l'aide d'un modèle simple des fonctions d'onde des porteurs dans la boîte. Des valeurs quantitatives de cette interaction sont données en tenant compte de la position de l'impureté dans la boîte ainsi que de sa réduction, induite par le confinement des porteurs. <br />Finalement, les possibilités pour contrôler cette interaction sont présentées: la modification de l'interaction par l'ajout de porteurs dans la boîte quantique, puis une augmentation possible de cette interaction grâce à un meilleur confinement des trous.

No description available.

<p>Currently, fossil fuels and nuclear power are our primary energy sources. However, both have critical disadvantages due to the limited supply and the hazard issues. Renewable energy research becomes one of most important research topics in the 21st century. Nanostructured materials show unique electrochemical properties in various energy conversion or storage devices. This dissertation starts with fundamental optical studies of nanomaterials (carbon nanotubes), followed by synthesizing novel nanomaterials for energy conversion (solar cells) and storage (lithium ion batteries) devices. </p><p> (1) There is an on-going debate concerning the ability of double walled carbon nanotubes (DWNTs) to exhibit photoluminescence (PL). We aim to clearly resolve this debate through the study of carefully separated DWNTs using density gradient ultra-centrifugation (DGU). Here, we clearly show that light is emitted from the inner wall of DWNTs. Interestingly, it was found that a very narrow range of diameters of the inner walls of DWNTs is required for photoluminescence (PL) to be observable. All other diameters led to complete PL quenching in DWNTs. (2) Inexpensive dye sensitized solar cells (DSSCs) on flexible plastic substrates have a bright future, but they require low temperature annealing (< 200°C). The method to fabricate low temperature DSSCs should resolve poor electron transfer between titanium dioxide (TiO2) nanoparticles (NPs) due to their incomplete contiguity and insulating layer of organic residues from binders in the photoactive film. Here, we have developed uniform CNTs/TiO2 composites for low temperature DSSCs by using modified sol gel method. DSSCs were fabricated to study incorporating functionalized few walled carbon nanotubes (f-FWNTs) effect on TiO2 NPs. Incorporating f-FWNTs can be beneficial for the low temperature annealing process of DSSCs to overcome extremely poor electron transport through TiO2 photoactive film. Incorporating f-FWNTs with TiO2 active layer improves electrons transport in some degree, but this advantage is limited. (3) Conductive fillers, such as amorphous carbon, carbon nanotube and graphene, have been mixed with nanostructured metal oxide materials to improve the performance of electrode materials in energy storage devices. However, ineffective junctions between conductive fillers are limiting the overall conductivity of the electrode. Therefore, we developed a convenient, inexpensive and scalable method for synthesizing hybrid carbon and titanium dioxide (C/TiO2) co-gels and co-aerogels to improve their electrochemical capacity in lithium ions batteries (LIBs). The monolith of the hybrid C/TiO2 co-aerogel can be directly used as active electrodes without the addition of binders. As a result, the capacitance of LIB anodes using the hybrid co-aerogel is significantly improved over current LIBs based on carbon/titanium oxide composite. Other metal oxides could also form co-gels with carbon to improve their potentials in numerous electrochemical, photocatalytic, and photoelectronic devices.</p> / Dissertation

The development of state-of-the-art AlGaN/GaN high electron mobility transistors (HEMTs) has shown much promise for advancing future RF and microwave communication systems. These revolutionary devices demonstrate great potential and superior performance and many commercial companies have demonstrated excellent reliability results based on multiple temperature accelerated stress testing. However, a physical understanding of the various reliability limiting mechanisms is lacking and the role and relative contribution of the various intrinsic material factors, such as physical stress and strain has not been clearly explained in the literature. Part of issues that impact device reliability are the mechanical stresses induced in the devices as well as the self-heating that also limit device performance. Thus, quantification of stress and temperature in AlGaN/GaN HEMTs is of great importance. To address some of the needs for metrology to quantify stress in AlGaN/GaN HEMTs, micro-Raman spectroscopy and micro-photoluminescence (micro-PL) were utilized to quantify the residual stress in these devices. Through the use of micro-Raman and micro-PL optical characterization methods, mapping of the vertical and lateral stress distributions in the device channels was performed. Results show that stress can be influenced by the substrate material as well as patterned structures including metal electrodes and passivation layers. Previously developed and reported micro-Raman thermometry methods require an extensive calibration process for each device investigated. To improve the implementation of micro-Raman thermometry, a method was developed which offers both experimental simplicity and high accuracy in temperature results utilizing a universal calibration method that can be applied to a broad range of GaN based devices. This eliminates the need for performing calibration on different devices. By utilizing this technique, it was revealed that under identical power dissipation levels, the bias conditions (combination of Vgs and Vds) alter the heat generation profile across the conductive channel and thus influence the degree of device peak temperature. The role of stress in the degradation of AlGaN/GaN HEMTs was also explored. A combined analysis using micro-Raman spectroscopy, coupled electro-thermo-mechanical simulation, and electrical step stress tests was conducted to investigate the link between performance degradation and the evolution of total stress in devices. It was found that in addition to stresses arising from the inverse piezoelectric effect, the substrate induced residual stress and the operational themo-elastic stress in the AlGaN layer play a major role in determining the onset of mechanically driven device degradation. Overall, these experiments were the first to suggest that a critical level of stress may exist at which point device degradation will start to occur. The optical characterization methods developed in this study show the ability to reveal unprecedented relationships between temperature/stress and device performance/reliability. They can be used as effective tools for facilitating improvement of the reliability of future AlGaN/GaN HEMTs.

L'étude de l'émission intégrée et résolue en temps de quatre configurations d'hétérostructures quantiques de type points-dans-un-fil d'InGaN/GaN nous a permis de déterminer la nature de la localisation et du mécanisme de recombinaison des porteurs de charge dans ces nanofils. Des mesures de comptage de photon unique correlés en temps (TCSPC) étendues sur une plage temporelle allant de 210 à 26000ns ont permis d'observer un comportement fortement non exponentiel de l'émission que nous avons déterminé être une loi de puissance. Nous avons trouvé que le temps de vie de l'émission diminue rapidement avec l'énergie d'émission. Par contre, l'observation d'un effet de la puissance d'excitation sur le temps de vie semble indiquer qu'à une énergie d'émission ne soit pas associée une seule dynamique d'émission à long temps. En utilisant une densité d'excitation laser de seulement quelques dizaines de watt par cm au carré, nous avons pu démontrer, en régime non perturbatif, que le profil des spectres d'émission intégrés en temps ainsi que la dynamique de l'évolution temporelle de l'émission étaient tout à fait compatibles avec une recombinaison radiative centrée sur une distribution de nano-agrégats riches en indium naturellement formés lors de la croissance des nanofils par MBE assistée par plasma. Cette conclusion est supportée par notre incapacité à observer l'effet Stark à confinement quantique, le succès d'un modèle de séparation de charges parfaitement compatible avec l'image des nano-agrégats d'indium et, finalement, par l'observation d'une émission principalement isotrope en polarisation. / We have performed time-integrated and time-resolved photoluminescence measurements on four different configurations of InGaN/GaN dot-in-a-wire heterostructures in order to further our understanding of the localization and radiative recombination mechanism involved in the process of emission. Time correlated single photon counting (TCSPC) measurements from 100 ns to 26000 ns have allowed us to observe a strong non-exponential decay which follows a power law on long time scale. The characteristic exponent of this power law is strongly correlated with the emission energy, causing the life-time of the emission to fall rapidly with increasing of its energies. The observation that the excitation power has an effect on the life-time shows that other factors such as the growth conditions must be involved in the coupling between life-time and energy. Using a low power density of a few tens of watts per cm squared, we have shown, in a non perturbative regime, that the shape of the time-integrated spectra and the dynamics of the time-resolved decay curves were consistent with a radiative recombination process centered on In-rich nanocluster. These nanoclusters naturally occur in the embedded InGaN inclusions during the growth by plasma-assisted MBE. This conclusion is supported by the absence of Quantum confined Stark effect. The success of a charge separation model is perfectly consistent with the emission centered on In-rich nanocluster and the observation of a quasiperfect isotropic emission. / Mesures effectuées dans le laboratoire de caractérisation optique des semi-conducteurs du Prof. Richard Leonelli du département de physique de l'université de Montréal. Les nanofils d'InGaN/GaN ont été fournis par le groupe du Prof. Zetian Mi du département de génie électrique et informatique de l'université McGill.

This thesis reports studies done on single-walled carbon nanotubes (SWNTs) using optical spectroscopy as the primary investigative technique. It focuses on advances in sample preparation which have been made possible through improvements to the method of photo-luminescence excitation (PLE) mapping of nanotubes. An introduction to the field and some theoretical models are presented initially to provide a background to the experimental chapters which follow. A description of the standard procedure for sample preparation in aqueous surfactants is then followed by a detailed introduction to PLE mapping, including modeling of SWNT spectra. The next chapter discusses improvements to the sample preparation method by using organic polymer solutions instead of aqueous surfactants for suspending the nanotubes. The results show reductions in the distribution of SWNT species which are solubilised, leading to significant improvements in the resolution of the optical absorbance spectra and an increased photoluminescence yield. Two experiments which were performed on the novel polymer-SWNT systems are then described. The first shows (via PLE mapping) that energy is transfered to the SWNTs when the polymer is photo-excited. The possible mechanisms behind this, as well as the implications for using carbon nanotubes as an additive in polymer photovoltaics, are discussed. The second experiment details a recent magneto-PL study of SWNTs embedded in films produced from the polymer solutions. Here, the improved optical signatures and absence of strain at low temperatures have revealed a previously unseen high field intensity dependence. The behavior has been explained by the magnetic field induced mixing of the excitonic states.

In this thesis, we investigate optical and electrical properties of dilute nitride semiconductors GaAsN in pulsed magnetic fields up to 62 T. For the most part, the experiments are performed at the Dresden High Magnetic Field Laboratory (HLD). In the first part of this thesis, the electron effective mass of GaAsN is determined with a direct method for the first time. Cyclotron resonance (CR) absorption spectroscopy is performed in Si-doped GaAsN epilayers with a nitrogen content up to 0.2%. For the CR absorption study, we use the combination of the free-electron laser FELBE and pulsed magnetic fields at the HLD, both located at the Helmholtz-Zentrum Dresden-Rossendorf. A slight increase of the CR electron effective mass with N content is obtained. This result is in excellent agreement with calculations based on the band anticrossing model and the empirical tight-binding method. We also find an increase of the band nonparabolicity with increasing N concentration in agreement with our calculations of the energy dependent momentum effective mass. In the second part of this thesis, the photoluminescence (PL) characteristics of intrinsic GaAsN and n-doped GaAsN:Si is studied. The PL of intrinsic and very dilute GaAsN is characterized by both GaAs-related transitions and N-induced features. These distinct peaks merge into a broad spectral band of localized excitons (LEs) when the N content is increased. This so-called LE-band exhibits a partially delocalized character because of overlapping exciton wave functions and an efficient interexcitonic population transfer. Merged spectra dominate the PL of all Si-doped GaAsN samples. They have contributions of free and localized excitons and are consequently blue-shifted with respect to LE-bands of intrinsic GaAsN. The highly merged PL profiles of GaAsN:Si are studied systematically for the first time with temperature-dependent time-resolved PL. The PL decay is predominantly monoexponential and has a strong energy dispersion. In comparison to formerly reported values of intrinsic GaAsN epilayers, the determined decay times of GaAsN:Si are reduced by a factor of 10 because of enhanced Shockley-Read-Hall and possibly Auger recombinations. In the third part of this thesis, intrinsic and Si-doped GaAsN are investigated with magneto-PL in fields up to 62 T. A magneto-PL setup for pulsed magnetic fields of the HLD was built for this purpose. The blue-shift of LE-bands is studied in high magnetic fields in order to investigate its delocalized character. The blue-shift is diminished in intrinsic GaAsN at higher temperatures, which indicates that the interexcitonic population transfer is only active below a critical temperature 20 K < T < 50 K. A similar increase of the temperature has no significant impact on the partially delocalized character of the merged spectral band of GaAsN:Si. We conclude that the interexcitonic transfer of Si-doped GaAsN is more complex than in undoped GaAsN. In order to determine reduced masses of undoped GaAsN and GaAs:Si, the field-induced shift of the free exciton transition is studied in the high-field limit. We find an excellent agreement of GaAs:Si with a formerly published value of intrinsic GaAs which was determined with the same method. In both cases, the reduced mass values are enhanced by 20% in comparison to the accepted reduced mass values of GaAs. The determined GaAsN masses are 1.5 times larger than in GaAs:Si and match the rising trend of formerly reported electron effective masses of GaAsN.

Mesures effectuées dans le laboratoire de caractérisation optique des semi-conducteurs du Prof. Richard Leonelli du département de physique de l'université de Montréal. Les nanofils d'InGaN/GaN ont été fournis par le groupe du Prof. Zetian Mi du département de génie électrique et informatique de l'université McGill. / L'étude de l'émission intégrée et résolue en temps de quatre configurations d'hétérostructures quantiques de type points-dans-un-fil d'InGaN/GaN nous a permis de déterminer la nature de la localisation et du mécanisme de recombinaison des porteurs de charge dans ces nanofils. Des mesures de comptage de photon unique correlés en temps (TCSPC) étendues sur une plage temporelle allant de 210 à 26000ns ont permis d'observer un comportement fortement non exponentiel de l'émission que nous avons déterminé être une loi de puissance. Nous avons trouvé que le temps de vie de l'émission diminue rapidement avec l'énergie d'émission. Par contre, l'observation d'un effet de la puissance d'excitation sur le temps de vie semble indiquer qu'à une énergie d'émission ne soit pas associée une seule dynamique d'émission à long temps. En utilisant une densité d'excitation laser de seulement quelques dizaines de watt par cm au carré, nous avons pu démontrer, en régime non perturbatif, que le profil des spectres d'émission intégrés en temps ainsi que la dynamique de l'évolution temporelle de l'émission étaient tout à fait compatibles avec une recombinaison radiative centrée sur une distribution de nano-agrégats riches en indium naturellement formés lors de la croissance des nanofils par MBE assistée par plasma. Cette conclusion est supportée par notre incapacité à observer l'effet Stark à confinement quantique, le succès d'un modèle de séparation de charges parfaitement compatible avec l'image des nano-agrégats d'indium et, finalement, par l'observation d'une émission principalement isotrope en polarisation. / We have performed time-integrated and time-resolved photoluminescence measurements on four different configurations of InGaN/GaN dot-in-a-wire heterostructures in order to further our understanding of the localization and radiative recombination mechanism involved in the process of emission. Time correlated single photon counting (TCSPC) measurements from 100 ns to 26000 ns have allowed us to observe a strong non-exponential decay which follows a power law on long time scale. The characteristic exponent of this power law is strongly correlated with the emission energy, causing the life-time of the emission to fall rapidly with increasing of its energies. The observation that the excitation power has an effect on the life-time shows that other factors such as the growth conditions must be involved in the coupling between life-time and energy. Using a low power density of a few tens of watts per cm squared, we have shown, in a non perturbative regime, that the shape of the time-integrated spectra and the dynamics of the time-resolved decay curves were consistent with a radiative recombination process centered on In-rich nanocluster. These nanoclusters naturally occur in the embedded InGaN inclusions during the growth by plasma-assisted MBE. This conclusion is supported by the absence of Quantum confined Stark effect. The success of a charge separation model is perfectly consistent with the emission centered on In-rich nanocluster and the observation of a quasiperfect isotropic emission.