Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 106-116).

Thesis (M.S.)--Ohio University, June, 2005. / Title from PDF t.p. Includes bibliographical references (p. 46-50)

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 157-165).

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 63-66).

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 80-84). Also available on the Internet.

Made available in DSpace on 2014-10-09T12:41:26Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:26Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Le transfert des données est le principal défi pour répondre à la demande croissante d’échange d’informations au 21eme siècle. Une amélioration possible des dispositifs actuels réside dans le passage vers une technologie d’interconnexions optiques. Cette thèse explore le développement de lasers à semi-conducteurs III-V à base de GaSb (III-Sb) épitaxiés par jets moléculaires (EJM) pour obtenir des sources laser émettant vers 1,55 µm, la gamme des télécommunications, et leur intégration sur substrat Si. Les III-Sb présentent des propriétés intéressantes en termes de relaxation des contraintes, mais sont plutôt adaptés pour une émission dans le moyen – infrarouge. Grâce à un nouveau dessin de zone active basé sur l’insertion de plans atomiques d’Al0.68In0.32Sb dans des puits quantiques Ga0.8In0 .2Sb nous avons obtenu par technologie en voie humide à l'Université de Montpellier des lasers GaSb fonctionnant en continu à température ambiante à 1,55 µm avec des performances comparables à l’état de l’art dans ce domaine. Par la suite, j'ai développé et optimisé au III – V Lab et à l’Université de Montpellier deux technologies basées sur la gravure sèche des structures. Cela a permis de réduire la largeur du ruban laser jusqu’à 1,5 µm, ce qui d’après mes simulations est nécessaire pour obtenir un fonctionnement monomode transverse du laser indispensable pour les applications en télécommunications. Nous avons également étudié la croissance EJM des III-Sb sur substrat Si pour intégrer directement les lasers sur ce substrat. Nous avons obtenu les premiers lasers GaSb intégrés sur Si fonctionnant en continu à température ambiante vers 1.55 µm. Pour un composant de 1 mm x 10 µm, le courant de seuil est de 300 mA et la puissance optique par facette non-traitée est de 3,2 mW à 500 mA de courant injecté. Ces résultats ouvrent la voie à l’intégration monolithique de lasers III-Sb sur plateformes Si pour des applications télécom. / The transfer of information is the main challenge to meet the growing demand of IT capacities in the 21st century. A possible improvement of existing devices is shifting to optical interconnects technology.This PhD explores the molecular-beam epitaxy (MBE) growth and development of antimonide (III-Sb) III-V semiconductor lasers for emission in the telecom range, near 1.55 µm, and their integration on Silicon substrates. III-Sb present interesting properties in term of strain relaxation but they are characterized by a natural emission in the mid – infrared range. Thanks to a new active zone design based on inserting monolayer-thin Al0.68In0.32Sb layers inside Ga0.8InSb QWs, we have obtained by wet processing at Université de Montpellier GaSb-based lasers working in continuous wave above room temperature, at the target wavelength. In addition, their performances were comparable to the performances of the well – established InP technology used in commercial telecom devices. Next, I have developed and optimized at both III-V Lab and Université de Montpellier new process flows based on dry etching of the structures. This allowed reducing the laser ridge width down to 1.5 µm, a value that modeling shows to be needed for single transverse-mode operation. In addition, we have investigated the MBE growth of III-Sb on Si substrates for the direct integration of lasers. We demonstrated the first cw, room temperature laser emission near 1.55 µm from GaSb devices integrated onto Si. For a 1 mm x 10µm diodes the threshold current was of 300 mA and the optical power per uncoated facet was 3.2 mW under 500 mA injected current. These results open the way to the monolithic integration on Si platforms of III-Sb devices for telecom applications.

abstract: The thesis studies new methods to fabricate optoelectronic Ge1-ySny/Si(100) alloys and investigate their photoluminescence (PL) properties for possible applications in Si-based photonics including IR lasers. The work initially investigated the origin of the difference between the PL spectrum of bulk Ge, dominated by indirect gap emission, and the PL spectrum of Ge-on-Si films, dominated by direct gap emission. It was found that the difference is due to the supression of self-absorption effects in Ge films, combined with a deviation from quasi-equilibrium conditions in the conduction band of undoped films. The latter is confirmed by a model suggesting that the deviation is caused by the shorter recombination lifetime in the films relative to bulk Ge. The knowledge acquired from this work was then utilized to study the PL properties of n-type Ge1-ySny/Si (y=0.004-0.04) samples grown via chemical vapor deposition of Ge2H6/SnD4/P(GeH3)3. It was found that the emission intensity (I) of these samples is at least 10x stronger than observed in un-doped counterparts and that the Idir/Iind ratio of direct over indirect gap emission increases for high-Sn contents due to the reduced gamma-L valley separation, as expected. Next the PL investigation was expanded to samples with y=0.05-0.09 grown via a new method using the more reactive Ge3H8 in place of Ge2H6. Optical quality, 1-um thick Ge1-ySny/Si(100) layers were produced using Ge3H10/SnD4 and found to exhibit strong, tunable PL near the threshold of the direct-indirect bandgap crossover. A byproduct of this study was the development of an enhanced process to produce Ge3H8, Ge4H10, and Ge5H12 analogs for application in ultra-low temperature deposition of Group-IV semiconductors. The thesis also studies synthesis routes of an entirely new class of semiconductor compounds and alloys described by Si5-2y(III-V)y (III=Al, V= As, P) comprising of specifically designed diamond-like structures based on a Si parent lattice incorporating isolated III-V units. The common theme of the two thesis topics is the development of new mono-crystalline materials on ubiquitous silicon platforms with the objective of enhancing the optoelectronic performance of Si and Ge semiconductors, potentially leading to the design of next generation optical devices including lasers, detectors and solar cells. / Dissertation/Thesis / Ph.D. Chemistry 2013

abstract: I studied the properties of novel Co2FeAl0.5Si0.5 (CFAS), ZnGeAs2, and FeS2 (pyrite) thin films for microelectronic applications ranging from spintronic to photovoltaic. CFAS is a half metal with theoretical spin polarization of 100%. I investigated its potential as a spin injector, for spintronic applications, by studying the critical steps involved in the injection of spin polarized electron populations from tunnel junctions containing CFAS electrodes. Epitaxial CFAS thin films with L21 structure and saturation magnetizations of over 1200 emu/cm3 were produced by optimization of the sputtering growth conditions. Point contact Andreev reflection measurements show that the spin polarization at the CFAS electrode surface exceeds 70%. Analyses of the electrical properties of tunnel junctions with a superconducting Pb counter-electrode indicate that transport through native Al oxide barriers is mostly from direct tunneling, while that through the native CFAS oxide barriers is not. ZnGeAs2 is a semiconductor comprised of only inexpensive and earth-abundant elements. The electronic structure and defect properties are similar in many ways to GaAs. Thus, in theory, efficient solar cells could be made with ZnGeAs2 if similar quality material to that of GaAs could be produced. To understand the thermochemistry and determine the rate limiting steps of ZnGeAs2 thin-film synthesis, the (a) thermal decomposition rate and (b) elemental composition and deposition rate of films were measured. It is concluded that the ZnGeAs2 thin film synthesis is a metastable process with an activation energy of 1.08±0.05 eV for the kinetically-limited decomposition rate and an evaporation coefficient of ~10-3. The thermochemical analysis presented here can be used to predict optimal conditions of ZnGeAs2 physical vapor deposition and thermal processing. Pyrite (FeS2) is another semiconductor that has tremendous potential for use in photovoltaic applications if high quality materials could be made. Here, I present the layer-by-layer growth of single-phase pyrite thin-films on heated substrates using sequential evaporation of Fe under high-vacuum followed by sulfidation at S pressures between 1 mTorr and 1 Torr. High-resolution transmission electron microscopy reveals high-quality, defect-free pyrite grains were produces by this method. It is demonstrated that epitaxial pyrite layer was produced on natural pyrite substrates with this method. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2013

Made available in DSpace on 2014-10-09T12:41:26Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:26Z (GMT). No. of bitstreams: 0 / No presente trabalho foi estudada a resposta de diodos epitaxiais (EPI) e fusão zonal (FZ) como dosímetros on-line em tratamentos radioterápicos com feixe de fótons na faixa de megavoltagem (diodo tipo EPI)e ortovoltagem (diodos tipo EPI e FZ). Para serem usados como dosímetros os diodos foram encapsulados em sondas de polimetilmetacrilato preto (PMMA). Para as medidas da fotocorrente os dispositivos foram conectados a um eletrômetro Keithley® 6517B no modo fotovoltaico. As irradiações foram feitas com feixes de fótons de 6 e 18 MV (acelerador Siemens Primus®),6 e 15 MV (acelerador Novalis TX®) e 10, 25, 30 e 50 kV de um equipamento de Radiação X Pantak/Seifert. Nas medidas com o acelerador Siemens Primus® os diodos foram posicionados entre placas de PMMA a uma profundidade de 10,0 cm e com o acelerador Novalis TX® mantidos entre placas de água sólida a uma profundidade de 5cm. Em ambos os casos, os diodos foram centralizados em campos de radiação de 10 × 10 cm2, com distância fonte superfície (DFS) mantida fixa em 100 cm. Para as medidas com os feixes de fótons deortovoltagem os diodos foram posicionados a 50 cm do tubo em um campo de radiação circular de 8 cm de diâmetro. A linearidade com a taxa de dose foi avaliada para as energias de 6 e 15MV do acelerador Novalis TX® variando-se a taxa de dose de 100 a 600 unidades monitoras por minuto e para o feixe de 50 kV variando-se a corrente do tubo de 2 a 20 mA. Todos os dispositivos apresentaram respostas lineares com a taxa de dose e dentro das incertezas, independência da carga com a mesma. Os sinais de corrente mostraram boa repetibilidade, caracterizada por coeficientes de variação em corrente (CV) inferiores a 1,14%(megavoltagem) e 0,15%(ortovoltagem) e em carga menores que 1,84% (megavoltagem) e 1,67% (ortovoltagem). Foram obtidas curvas dose-resposta lineares com coeficientes de correlação linear melhores que 0,9999 para todos os diodos. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP