No description available.

No description available.

Une des sources d'énergie les plus abondantes est le soleil, d'où l'importance de développer des techniques efficaces pour convertir les rayons solaires en électricité. Plusieurs dispositifs peuvent être employés, dont les cellules photovoltaïques électrochimiques (CPE). Le fonctionnement de certains types de CPE repose sur une jonction entre un semi-conducteur de type n et un électrolyte gel. Le semi-conducteur, une des composantes majeures des CPE, peut être amélioré. Dans ce travail, il est question du développement d'une nouvelle méthode de préparation du semi-conducteur CulnS₂ en couche mince. Elle consiste à électrodéposer galvanostatiquement le film sur un substrat de titane. L'optimisation de la méthode inclut le choix du courant de déposition, de la méthode de recuit et du traitement chimique au KCN. Le courant de déposition a été optimisé à -40 mA, menant à des films homogènes possédant des pourcentages de CulnS₂ et de cristallinité intéressants. Un recuit sous vide à 425°C permet d'obtenir des films plus cristallins, pratiquement non-oxydés et plus purs. Enfin, un traitement chimique au KCN 0,25 M à température pièce pendant environ 10 secondes, qui permet de diminuer la quantité de cuivre dans les films, a donné les meilleurs résultats. La structure du CulnS₂ a été définie comme étant tétragonale chalcopyrite avec des paramètres de maille de 5,549 Å pour a et b, et de 11,02 Å pour c. Le facteur de rugosité moyen des films est de 19 avant traitement chimique et de 13 après traitement au KCN, avec une épaisseur moyenne de 4,2 µm. La valeur de la bande interdite a été déterminée à 1,51 eV, ce qui est comparable à la théorie. Pour les films ayant subi un traitement au KCN, une densité de porteurs de charge majoritaires de 3,8x10¹⁹ cm⁻³ a été calculée, ainsi qu'un potentiel de bandes plates de -0,45 V vs ENH. Deux piles de configuration n-CuInS₂ | PVdF (20% massique) / DMF/DMSO (60%/40% volumique), CsT 1,3 M/T₂ 0,13 M (80 % massique) | ITO ont été caractérisées dans l'obscurité. PVdF représente le polyvinylidène de fluor, CsT le 5-mercapto-1-méthyltétrazolate de césium et T₂ son disulfure. Une semi-conductivité de type n a été observée, comme attendue, avec un facteur de rectification de 2,82 (à 0,5 V) lorsque le CuInS₂ était traité au KCN. La densité de courant d'échange a été calculée à 2,7 µA/cm₂, la résistance shunt à 46 kΩ et la constante d'idéalité à 2,6 pour la même cellule. Les résultats montrent que les films ayant subi un traitement au KCN présentent une interface CulnS₂/électrolyte gel de meilleure qualité. Les films semi-conducteurs préparés dans ce projet semblent améliorer la qualité de cette interface par rapport aux films obtenus par électrodéposition potentiostatique. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Semi-conducteur, CuInS₂, pile solaire, électrodéposition galvanostatique.

The development of next generation devices for high speed switching, high efficiency energy conversion, spintronic devices require the development of advanced material systems. While conventional group IV, group II-VI and group III-V based materials systems have served as a base material in many modern device structures, they posses fundamental materials properties that limit their suitability in next generation device structures. The group III-N material system is very promising for the development of advanced device structures. GaN is currently widely used in high efficiency lighting applications. However, the development of this material system has been limited to material systems with limited indium. The growth of high indium concentration materials such as InN and GaxIn1-xN has proven difficulty due to the high thermal decomposition pressure of InN. In response to this difficulty, a high pressure chemical vapor deposition reactor system has been developed for the growth of InN which enables elevated processing temperatures as compared to conventional low-pressure growth techniques. The design criteria and implementation of this unique design is presented here. In addition, the results of in-situ real time optical characterization capabilities of this reactor system are presented as applied to thermal characterization, flow dynamics, gas phase kinetics and surface reactions. Ex-situ InN thin films grown on sapphire substrates and GaN epilayers have been analyzed by x-ray diffraction, transmission spectroscopy and raman spectroscopy. These results indicated single crystal indium nitride films with an optical absorption edge which varies between 0.7 and 1.9 eV as a function of precursor flow stoichiometry.

The purpose of the thesis is to investigate the improvement of single-crystal Si solar cell efficiency using porous Indium tin oxide (ITO)/ITO double layer antireflection(AR) coating. The resistivity, transmittance and refraction index of the porous ITO films prepared by supercritical CO2 treatment were investigated. At a 2000 psi pressure and 60¡CC, the resistivity of porous ITO films is 15 £[-cm, the average transmittance is better than 95 %, and the refraction index is 1.54. In addition, the resistivity of ITO thin films fabricated by reactive ratio-frequency magnetron sputtering is 7¡Ñ10-4 £[-cm, the average transmittance are 85 %, and the refraction index is 2.0. For the single crystal-Si solar cell with porous ITO/ITO double layer AR coating, the open circuit voltage, short circuit current, fill factor and efficiency are measured.

In this studing, application of the digital image correlation method (DIC) for determining the coefficient of thermal expansion (CTE) of Indium Tin Oxide/Polyethylene Terephthalate(ITO/PET) thin film/flexible substrate was proposed and the effects of thinkness variations of ITO and PET, respectively, on the CTE of the specimens was disscussed. The observation range of experimental temperature was chosen from room temperature to the glass transfer temperature of PET, 70¢J. A novel DIC experimental process for reducing the errors caused from the variations of the refractive index of the surrounding heated air was proposed. As a result, the experimental error of CTE measurement was reduced form 10~17% to less than 5%. The experimental results showed that the CTE of ITO/PET specimen is anisotropic. Futhermore, the CTE of an ITO/PET specimen will be increased by decreasing the thinkness of PET flexible substrate, and increased by increasing the thinkness of ITO film - which means decreasing the surface resistance of ITO film.

In the study, conductive distributed Bragg reflectors (DBRs) fabricated at room temperature based on porous indium tin oxide (ITO) on dense ITO bilayers were proposed for resonant cavity organic light emitting diodes (RCOLEDs). In the fabrication of the ITO DBRs, the low refractive index porous ITO films were obtained by applying supercritical CO2 treatment at different temperature and pressures on the spin-coated sol-gel ITO films. On the other hand, the high refractive index ITO films were grown at room temperature by long-throw reactive ratio-frequency magnetron sputtering. The refractive index of the porous ITO film and ITO films were 1.54 and 2.0, respectively. For the DBR with 4 pairs ITO bilayers, the optical reflectance of more than 70 % was achieved. The stop band and the average resistivity is 140 nm and 2.2¡Ñ10-3 £[-cm, respectively. Finally, electrical and optical characteristics of the RCOLEDs fabricated on the ITO DBR were investigated and compared with those of the conventional OLEDs. The maximum luminous efficiency of 3.79 cd/A was obtained at 347 mA/cm2 for the RCOLED. This luminous efficiency was 26 % higher than that of the conventional OLED.

No description available.

This thesis describes the development of III-Nitride materials for light emitting applications. The goals of this research were to create and optimize a green light emitting diode (LED) and laser diode (LD). Metalorganic chemical vapor deposition (MOCVD) was the technique used to grow the epitaxial structures for these devices. The active regions of III-Nitride based LEDs are composed of InₓGa₁₋ₓN, the bandgap of which can be tuned to attain the desired wavelength depending on the percent composition of Indium. An issue with this design is that the optimal growth temperature of InGaN is lower than that of GaN, making the growth temperature of the top p-layers critical to the device performance. Thus, an InGaN:Mg layer was used as the hole injection and p-contact layers for a green led, which can be grown at a lower temperature than GaN:Mg in order to maintain the integrity of the active region. However, the use of InGaN comes with its own set of drawbacks, specifically the formation of V-defects. Several methods were investigated to suppress these defects such as graded p-layers, short period supper lattices, and native GaN substrates. As a result, LEDs emitting at ~532 nm were realized. The epitaxial structure for a III-Nitride LD is more complicated than that of an LED, and so it faces many of the same technical challenges and then some. Strain engineering and defect reduction were the primary focuses of optimization in this study. Superlattice based cladding layers, native GaN substrates, InGaN waveguides, and doping optimization were all utilized to lower the probability of defect formation. This thesis reports on the realization of a 454 nm LD, with higher wavelength devices to follow the same developmental path.

A logical progression from the maturing field of colloidal semiconductor quantum dots to the emerging subclass of impurity-doped colloidal semiconductor nanoparticles is underway. To this end, the present work describes the formation and analysis of a new form of Tin-doped Indium Oxide (ITO). The form is that of a colloidal dispersion comprised of pure-phase, 4-6 nanometer ITO particles possessing an essentially single crystalline character. This system forms a non-agglomerated, optically clear solution in a variety of non-polar solvents and can remain in this state, at room temperature, for months and potentially, years. ITO is the most widely used member of the exotic materials family known as Transparent Conductive Oxides (TCOs) and is the primary enabling material behind a wide variety of opto-electronic device technologies. Material synthesis was achieved by initiating a series of interrelated nucleophilic substitution reactions that provided sufficient intensity to promote doping efficiencies greater than 90% for a wide range of tin concentrations. The optical clarity of this colloidal system allowed the intrinsic properties of single crystalline ITO particles to be evaluated prior to their use in thin-films or composite structures. Monitoring the temporal progression of n-type degeneracy by its effects on the optical properties of colloidal dispersions shed light on the fundamental issues of particle formation, band filling (Burstein-Moss) dynamics, and the very origin of n-type degeneracy in ITO. Central to these studies was the issue of excess electron character. The two limiting cases of entirely free and entirely confined electron motion were evaluated by application of bulk-like band dispersion analysis and the effective mass approximation, respectively. This provided a means to estimate the number of excess conduction band electrons present within an individual particle boundary. The ability to control and optimize the level of n-type degeneracy within the colloidal ITO nanoparticle form by compositional variation was also demonstrated. A key to the widespread adoption of a new material by industry is an ability to produce multi-gram and perhaps, kilogram quantities with no significant sacrifice in quality. Accordingly, a modified synthesis process was developed to allow for the mass production of high-quality colloidal ITO nanocrystals.