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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.

[pt] Este trabalho apresenta os resultados de um estudo que envolve a fabricação e a caracterização de dispositivos orgânicos emissores de luz (OLEDs) baseados em complexos β-dicetonatos de terras-raras. O estudo se coloca como continuação lógica da linha de pesquisa em dispositivos eletroluminescentes baseados em íons terras-raras, começada alguns anos atrás neste grupo de pesquisa. Para a produção dos dispositivos foram empregadas várias técnicas de deposição de filmes finos, tais como deposição térmica resistiva, pulverização catódica assistida por plasma (rf-magnetronsputtering) e spin-coating. A síntese dos compostos orgânicos, bem como alguns estudos adicionais puderam ser realizadas através de colaborações com diversos grupos de pesquisas nacionais, os quais dispõem de recursos e capacitação em áreas complementares. Os complexos orgânicos estudados foram divididos em três conjuntos, que chamamos de sistemas. No sistema 1, estudou-se o complexo Eu(bmdm)3(ttpo)2, onde o ligante orgânico bmdm é um conhecido agente absorvedor de radiação UV bastante usado em protetores solares. Os OLEDs baseados neste complexo apresentaram intensa foto- e eletroluminescência com alta pureza de cor dada apenas pelas finas transições características do íon Eu3+. No sistema 2, estudou-se o complexo chamado de binuclear. Este composto tem dois núcleos terras-raras coordenados numa mesma molécula. O primeiro binuclear estudado, o complexo Eu(btfa)3 phenterpy Tb(acac)3, não apresentou as transições características dos íons Tb3+ e Eu3+ como era esperado inicialmente. Por outro lado, apresentou uma eletroluminescência sintonizável em duas situações distintas, a primeira em função da tensão aplicada e a segunda através de mudanças na arquitetura das camadas constituintes. Por causa desse efeito, mostramos a possibilidade de se construir um dispositivo OLED emissor de luz branca. Ainda nesse sistema, foram estudados OLEDs com complexos modificados quimicamente, chamados de binuclear 2 e trinuclear. O complexo binuclear 2 apresentou as linhas de emissão dos íons Tb3+ e Eu3+. Apesar de menos eficiente que o primeiro complexo binuclear, este estudo mostrou que através de manipulações moleculares (nanotecnologia) é possível sintetizar compostos capazes de emitir as linhas características de emissão dos íons terras-raras, ou seja, com um único complexo é possível obter duas emissões distintas. Por último, ainda como sistema 2, o complexo trinuclear, é uma mistura de compostos orgânicos contendo Tm, Tb e Eu e não formam uma única molécula, como no caso dos compostos binucleares. Este estudo foi iniciado recentemente e ainda não foi completamente explorado. Os primeiros testes mostraram que é possível usar este complexo também para fabricar OLEDs com emissão de cor branca, variando-se as quantidades relativas de Tm, Tb e Eu da mistura. Sabendo-se que os ligantes β-dicetonas são os responsáveis pela transferência de energia para os íons TR3+, através do efeito antena, o sistema 3, despontou como grande novidade, mostrando a construção de dispositivos eletroluminescentes baseados em complexos tetrakis(β-dicetonatos) de TR, ou seja, compostos que possuem quatro ligantes β-dicetonas coordenandos a um único íon TR. Com esse sistema conseguimos pela primeira vez uma emissão eficiente e pura das principais transições do íon Tb à temperatura ambiente. O trabalho apontou, também, que tanto a irradiação com luz UV, quanto a exposição aos agentes atmosféricos (oxigênio, água, umidade, etc.) contribuem para uma rápida degradação dos complexos orgânicos com conseqüente decaimento do desempenho dos dispositivos fabricados. Para tanto, iniciamos um estudo para investigar as causas da degradação de alguns dos compostos orgânicos utilizados na fabricação de OLEDs. Os estudos de fotoabsorção e fotoemissão realizados no Laboratório Nacional de Luz Síncrotron foram fundamentais para uma maior compreensão destes efeitos. Os resultados deste estudo mostraram que as técnicas espectroscópicas empregadas neste trabalho podem ser utilizadas para se investigar a estrutura eletrônica, bem como a fotodegradação de compostos orgânicos usados na fabricação de OLEDs. Utilizando a espectroscopia de fluorescência, se estudou a viabilidade de se construir um dosímetro de radiação ultravioleta portátil e de uso pessoal usando um OLED cuja eletroluminescência é sensível à radiação UV. / [en] In this work we present the results of a study that involves the manufacture and the characterization of organic eletroluminescent devices (OLEDs) based on (beta)-diketonates Rare-Earth complexes. The investigation reported is a continuation of the research in electroluminescent devices based on rare-earth ions, started some years ago in our Group. For the production of the devices were applied several thin films deposition techniques: thermal resistive, rf-magnetronsputtering and spin-coating. The synthesis of organic compounds, as well some additional studies, were carried on through the collaboration with different brazilian research groups, which have resources and qualification in complementary areas. The organic compounds studied in this thesis have been divided in three groups, named systems. In system 1, the studied complex was Eu(bmdm)3(ttpo)2, where the organic bmdm ligand is a known UV sensitive material, frequently used in sunblockers. The OLEDs based on this complex presented intense photo- and electroluminescence with high pure color emission due to the almost atomic transitions characteristic of the Eu3+ ion. In system 2, a binuclear complex, represented by the molecular formula Eu(btfa)3 phenterpy Tb(acac)3 was studied. This complex has two rare-earth nuclei coordinated in the same molecule. The OLEDs based on this complex did not present the Tb3+ and Eu3+ characteristic transitions as expected. On the other hand, the complex gave us the possibility to develop an OLED with white color emission. Probably the major novelty of this thesis is represented by system 3. Indeed, knowing that the (beta)-diketone ligands are the main responsible for the RE3+ ions energy transference through the antenna effect, in system 3, we investigated the possibility to fabricate electroluminescent devices based on RE (beta)-diketonate tetrakis complexes, which have four coordinated (beta)- diketones ligand to an RE ion in order to enchance the energy transfer and the emission efficiency. With this system we obtained, for the first time, an efficient and pure Tb emission at room temperature.

[pt] Neste trabalho são apresentados os resultados da produção e caracterização de novos dispositivos orgânicos eletroluminescentes (OLEDs), que podem ser divididos idealmente em três grupos. O primeiro composto pelos OLEDs que utilizam os distirilbenzenos (DSBs) como camada eletroluminescente. Os DSBs são sistemas utilizados em química supramolecular como pontes para transferência de carga. No segundo colocamos os OLEDs baseados em 2; 6 - bis(dietanolamina) - 4; 8 - dipiperidinopirimida (5; 4-d) pirimidina (DIP), que é uma droga amplamente conhecida e utilizada no tratamento de doenças cardiovasculares, que por possuir uma intensa fluorescência despertou a curiosidade para investigarmos a possibilidade da sua utilização com camada eletroluminescente. A utilização do DIP como camada eletroluminescente resultou em um OLED com a maior luminância dos grupos estudados, 1500 cd/m2. O terceiro grupo é formado por OLEDs que utilizam moléculas de calixarenos ([Al . 1]3+ e [Zn . 1]2+ onde 1 = 8- oxiquinolinacalix[4]areno) como camada transportadora de elétrons e eletroluminescente. Foram estudados dois sistemas calixarenos, o primeiro sistema é coordenado com alumínio (calix[Al]3+) e o segundo coordenado com zinco (calix[Zn]2+). O sistema calix[Al]3+ apresentou uma interessante propriedade de cooperação entre o anel central calix e um grupamento quinolina coordenado com Al. Utilizando este mecanismo de sinergia produzimos um OLED sintonizável, o qual varia o pico de sua banda de eletroluminescência de 510 nm pra 470 nm em função da tensão aplicada. Desta forma a cor da luz emitida pelo dispositivo pode ser variada com continuidade do azul (X=0,26 : Y=0,33 coordenadas CIE) até o verde claro (X=0,18 : Y=0,25).Todos os sistemas orgânicos foram analisados de um ponto de vista térmico através da analise de calorimetria diferencial de varredura (DSC), com a qual determinamos sua temperatura de transição vítrea (Tg). Com o auxilio de medidas eletroquímicas, estabelecemos um procedimento experimental simples e rápido para determinar os níveis energéticos HOMO (highest occupied molecular orbital) dos materiais orgânicos estudados na forma de filmes. Enfim, através da caracterização elétrica foi possível determinar o tipo de injeção de portadores que governa os dispositivos bem como o modelo que controla o transporte de cargas no interior dos OLEDs. / [en] In this work the results of the production and characterization of new organic electroluminescent devices (OLEDs) are presented and discussed. The work can be ideally divided in three parts. The first is composed by the OLEDs that use the distyrilbenzene (DSBs) compounds as electroluminescent layer. The DSBs are systems used in supramolecular Chemistry as bridges for load transfer. This is the first time that they are used in small molecule OLEDs. The second part deals with OLEDs based on dipyridamole (2; 6-bis(diethanolamino) - 4; 8 - dipiperidinopyrimido (5; 4-d)pyrimidine) (DIP) molecule, which is a very well known anti-platelet drug thoroughly used in the treatment of hearth diseases that for possessing an intense fluorescence woke up our curiosity in order to investigate the possibility of its use as electroluminescent layer. The use of DIP as electroluminescent layer resulted in a particular OLED with the highest luminance of the investigated devices, about 1500 cd/m2. Finally, the third part involves OLEDs that use calixarenes molecules [Al . 1]3+ and [Zn . 1] 2+ (1 = 8- oxyquinolinecalix[4]arene) as electroluminescent and electron transporting layer. In this work were studied two calixarenes systems: the first system is coordinated with aluminum (calix[Al]3+) and the second one is coordinated with zinc (calix[Zn]2+). The first one presented an interesting cooperation property among the central calix ring and the quinolina group coordinated with the Al metal. Using this synergic mechanism we were able to produce a tunable OLED, which electroluminescent emission varies continuously from 510 nm to 446 nm as a function of the applied bias voltage. All the organic compounds used in this work were analyzed from a thermal point of view through a Differential Scanning Calorimetry (DSC), in order to determine their transition glass temperature (Tg). By using electrochemistry measurements it was possible to establish a systematic and simple experimental procedure to determine the HOMO (highest occupied molecular orbital) energy levels of the organic materials studied in the form of films. Finally, through the electrical characterization it was possible to determine the type of carrier injection that governs the fabricated devices as well as the model that controls the carrier transport inside the OLEDs.

In this research, we investigated a novel rigid-rod polymer sPBI for mono-layer polymer light emitting diode (PLED) fabrication and luminescence emission. sPBI could be a luminescent polymer with a low threshold voltage of 4.5 V and green light electroluminescence emission (530 nm). Its SO3H pendant attached to the p-phenyl ring improved electronic delocalization along the backbone resulted in a red shift of the absorption spectrum. By attaching propanesulfonated pendants to the heterocyclic moiety of intractable fully conjugated sPBI, water-soluble rigid-rod polyelectrolyte sPBI-PS(Li+) was synthesized to promote its processibility in water or common organic solvent. This water-soluble rigid-rod polyelectrolyte sPBI-PS(Li+) was fabricated for polymer light-emitting electrochemical cells (PLECs) with LiCF3SO3 (LiTf) or LiN(CF3SO2)2 (LiTfSI) dopants for investigating the influence of propanesulfonated pendants as well as dopants on the opto-electronic emission and the room-temperature DC conductivity. The effect of lithium salts (LiTf or LiTfSI) on photoluminescence color of doped sPBI-PS(Li+) films was negligible. sPBI-PS(Li+) PLECs doped with 0.41 and 1.01 wt. % of LiTfSI showed higher green light electroluminescence emission (514 nm) with a lower threshold voltage of 3.0 V and -4.6 V, respectively. Emission brightness of the sPBI-PS(Li+) PLEC did not raise upon increasing the ionic conductivity of the luminescent layer.

ABSTRACT Light emitting diodes of non-fully conjugated coil-like homopolymers and fully conjugated rigid-rod homopolymers with electron withdrawing or donating group were studied. A series of Poly[2,2-(m-2-X-phenylene)-4-4¡A-hexafluoroisopropane- bibenzoxazoles] (6F-PBO-X, with X = amine, hydrogen and nitro) and poly-p-(2-X- phenylene)-benzobisoxazole (PBO-X, with X = amine, hydrogen and nitro) were synthesized for light emitting diode applications to observe electroluminescence emission affected by electron withdrawing or donating group. All polymers were fabricated identically to form bi-layer light emitting diodes. In the devices, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonite)(PEDOT:PSS) was applied to be a hole transport layer; indium tin oxide (ITO) was the anode; and aluminum was the cathode. Devices of the non-fully conjugated coli-like polymers (6F-PBO-X) and the fully conjugated rigid-rod polymers (PBO-X) all showed threshold voltage about 4 V. In the electroluminescence (EL) spectrum, the maximum intensity of non-fully conjugated polymer (6F-PBO-X) with amine (-NH2), hydrogen (-H) or nitro (-NO2) functional group was at 499 nm, 505 nm and 515 nm, respectively, showing a 20 nm wavelength shift. From ¡VNH2, -H and ¡VNO2 groups, their Commission International de l`Eclairage (C. I. E.) coordinates were (0.30, 0.46), (0.34, 0.45) and (0.40, 0.46), respectively. The EL maximum intensity for fully conjugated rigid-rod polymer PBO-X was at 521 nm (-NH2) and 474 nm (-NO2) showing a 50 nm wavelength shift. Their C. I. E. coordinates were (0.42, 0.45) and (0.25, 0.38), respectively. This is attributed to the fully conjugated, collinear, coplanar, rigid-rod polymers (PBO-X) backbone readily affected by the push-pull functional groups showing a large red shift.

Light emitting transistors (LETs) and transistor lasers (TLs) are newly-emerging optoelectronic devices capable of emitting spontaneous or stimulated light while performing transistor actions. This dissertation describes the design, growth, and performances of long wavelength LETs and TLs based on InAlGaAs/InP material system. First, the doping behaviors of zinc (Zn) and carbon (C) in InAlGaAs layers for p-type doping were investigated. Using both dopants, the N-InP/p-In0.52(AlxGa1-x)0.48As/N-In0.52Al0.48As LETs with InGaAs quantum wells (QWs) in the base demonstrate both light emission and current gains (β). The device performances of Zn- and C-doped LETs have been compared, which is explained by a charge control analysis involving the quantum capture and recombination process in the QWs. A TL based on a C-doped double heterostructure (DH-TL) with single QW was designed and fabricated. The device lases at 77 K with a threshold current density (Jth) of 2.25 kA/cm2, emission wavelength (λ) at ~1.55 µm, and β of 0.02. The strong intervalence band absorption (IVBA) is considered as the main intrinsic optical loss that prohibits the device from lasing at room temperature. Based on a threshold condition analysis taking into account the strong IVBA, it is found that room-temperature lasing of a DH-TL is achieved only when the base thickness and doping level are within a specific narrow range and improved performance is expected in a separate confinement heterostructure (SCH) TL.

In dieser Arbeit werden zwei Schwerpunkte behandelt. Zum Einen soll der Einsatz nanoskaliger Materialien als Funktionskomponenten in Elektrolumineszenzbauteilen beschrieben werden. Dabei wird in einem ersten Aufbau ein transparenter Nanokompositfilm als emittierende Schicht in einem, den organischen Leuchtdioden, analogen Aufbau eingesetzt, während in einer zweiten Struktur eine transparente Elektrode, die auf nanoskaligen Kohlenstoffmaterialien (Kohlenstoffnanoröhren bzw. Graphenen) basiert, hinsichtlich ihrer Eignung als Alternative zu etablierten transparenten Elektroden untersucht werden soll. In weiterführenden Arbeiten werden die Erfahrungen aus der Graphensynthese auf die Generierung poröser, funktionalisierter Kohlenstoffmaterialien angewendet. Verbindend, wird die Röntgenkleinwinkelstreuung eingesetzt, um in vergleichenden Untersuchungen möglichst detailierte Informationen über die jeweiligen Systeme zu erhalten.

Ce travail de thèse est une contribution au développement d'afficheurs électroluminescents inorganiques utilisant le luminophore CaTiO3 :Pr3+ comme couche active. Il comporte deux volets. Le premier concerne l'étude du dépôt de CaTiO3 :Pr3+ par pulvérisation cathodique à partir d'une cible céramique élaborée au laboratoire et s'est plus particulièrement attaché à l'influence de la pression de dépôt et aux conditions de recuit (température, type de fours) sur les propriétés morphologiques, structurales, optiques et électriques des films. Les films obtenus sont cristallisés en structure orthorhombique, photoluminescents, transparents sur toute la gamme du visible et possèdent des propriétés électriques compatibles avec l'application visée. Des pistes d'optimisation de ces propriétés sont également avancées. Le second volet du travail utilise le modèle de transfert de charge par intervalence (TCIV) développé ces dernières années au laboratoire, pour orienter la recherche d'autres luminophores dopés par des ions Pr3+ utilisables dans des afficheurs électroluminescents. Sur cette base, des titanates de formulations (Ca,Sr)TiO3 :Pr3+, CaTiO3 :Bi3+ ;Pr3+ et Na1/2Ln1/2TiO3 :Pr3+ (Ln = La, Gd, Y, Lu) ont été synthétisés et caractérisés. L'évaluation détaillée du comportement de ces matériaux en photoluminescence a permis de valider le modèle TCIV, d'initier d'autres modèles et de mettre en évidence l'intérêt d'un codopage au bismuth pour accroître l'intensité de fluorescence de l'ion Pr3+ dans la matrice CaTiO3. Le luminophore rouge CaTiO3 :Bi3+ ; Pr3+ apparaît être un candidat intéressant pour des applications en électroluminescence.

In this study, silicon nanocrystals (NC) were synthesized in silicon dioxide matrix by ion implantation followed by high temperature annealing. Annealing temperature and duration were varied to study their effect on the nanocrystal formation and optical properties. Implantation of silicon ions was performed with different energy and dose depending on the oxide thickness on the silicon substrate. Before device fabrication, photoluminescence (PL) measurement was performed for each sample. From PL measurement it was observed that, PL emission depends on nanocrystal size determined by the parameters of implantation and annealing process. The peak position of PL emission was found to shifts toward higher wavelength when the dose of implanted Si increased. Two PL emission bands were observed in most cases. PL emission around 800 nm originated from Si NC in oxide matrix. Other emissions can be attributed to the luminescent defects in oxide or oxide/NC interface. In order to see electroluminescence properties Light Emitting Devices (LED) were fabricated by using metal oxide semiconductor structure, current-voltage (I-V) and electroluminescence (EL) measurements were conducted. I-V results revealed that, current passing through device depends on both implanted Si dose and annealing parameters. Current increases with increasing dose as one might expect due to the increased amount of defects in the matrix. The current however decreases with increasing annealing temperature and duration, which imply that, NC in oxide behave like a well controlled trap level for charge transport. From EL measurements, few differences were observed between EL and PL results. These differences can be attributed to the different excitation and emission mechanisms in PL and EL process. Upon comparision, EL emission was found to be inefficient due to the asymmetric charge injection from substrate and top contact. Peak position of EL emission was blue shifted with respect to PL one, and approached towards PL peak position as applied voltage increased. From the results of the EL measurements, EL emission mechanisms was attributed to tunneling of electron hole pairs from top contact and substrate to NC via oxide barrier.