La manipulation de parois de domaine magnétique – qui séparent des régions d’aimantation uniforme dans les matériaux – est associée à des enjeux à la fois fondamentaux et technologiques. De nombreux travaux portent sur l’utilisation de champs magnétiques et de courants électriques pour leur déplacement. Cependant, des préoccupations particulières – notamment la dissipation d’énergie - motivent la recherche d’alternatives. Parmi les solutions potentielles, le couplage magnétoélectrique par l’intermédiaire de contraintes mécaniques dans des hétérostructures magnétoélastique/piézoélectrique paraît prometteur. Dans cette thèse, il est montré que l’association d’un champ magnétique de biais et de contraintes mécaniques uniformes peut engendrer le déplacement unidirectionnel d’une paroi de domaine transverse dans des nanostructures à anisotropie uniaxiale. Les considérations statiques et dynamiques de ce phénomène sont étudiées par le biais de procédures numériques ad hoc simulant le couplage mécanique entre substrat de PMN-PT de coupe 011 générant des contraintes, et nanostructures multicouches magnétoélastiques TbCo2/FeCo. Le design du profil de section des nanostructures permet de moduler la réponse du système, par exemple pour contrôler la position de parois confinées. La dynamique du système se distingue des régimes habituels de par la forme de la paroi de domaine. L’atteinte de régimes permanents dans des nanorubans montre que des vitesses comparables aux autres techniques sont obtenues, pour une dissipation d’énergie beaucoup plus faible. Des travaux expérimentaux ont permis de mettre au point un process de fabrication sur PMN-PT et d’explorer l’effet magnétoélectrique / The manipulation of magnetic domain walls – that separate regions of uniform magnetization – is associated with both fundamental and technological research interests. A large part of the literature on domain wall motion deals with the use of magnetic fields and electric currents. However, several concerns – most notably energy dissipation – motivates the search for alternatives. Among potential candidates, the mechanical stress-mediated magnetoelectric coupling in magnetoelastic/piezoelectric heterostructures seems promising. In this thesis, it is shown that the combination of a bias magnetic field and uniform mechanical stress can induce unidirectional domain wall motion in nanostructures with uniaxial anisotropy. Static and dynamic aspects of this phenomenon are studied by means of ad hoc numerical procedures simulating the mechanical coupling of 011-cut PMN-PT generating the stress, and TbCo2/FeCo multilayers magnetoelastic nanostructures. The design of the cross section profile in nanostructures allows to tailor the response of the system, enabling for instance the control of domain wall position in confined geometries. The associated dynamics stands apart from known regimes because of the shape of the domain wall. The existence of steady-state regimes in nanostripes of constant width shows that velocities comparable to those of other techniques can be obtained, for a fraction of the energy required. Experimental investigations resulted in the development of a successful fabrication process on PMN-PT and the exploration of the magnetoelectric effect

La spintronique est un nouveau domaine de recherche qui exploite l'influence de la caractéristique quantique de l’électron (le spin) sur la conduction électrique. Pour réaliser des composants de spintronique innovants, l’obtention des semi-conducteurs ferromagnétiques à température ambiante devenait un challenge international. Dans ce contexte, après les premières prédictions théoriques de la haute température de Curie de Zn1-xCoxO et les rapports contradictoires sur l'état magnétique de ce système, nous nous sommes attaché à étudier le semi-conducteur magnétique dilué Zn1-xCoxO. Une étude ab initio des propriétés structurales, électroniques et magnétiques du Zn1-xCoxO a été effectuée en utilisant la méthode de pseudopotentiels dans le cadre de la théorie de la fonctionnelle de la densité (DFT) avec les deux approximations GGA et GGA+U. En parallèle, des films minces de Zn1-xCoxO ont été synthétisés par co-pulvérisation cathodique magnétron en condition réactive avec différentes conditions d’élaboration. Les propriétés structurales, morphologiques, électriques et magnétiques ont été analysées par différentes techniques de caractérisation et confrontées à celles obtenues par l’étude ab inito. / Spintronic is a new field of research exploiting the effect of the quantum property of the electron (spin) on the electrical conduction. In order to realize innovative spintronic components, ferromagnetic semiconductors obtained at room temperature became an international challenge. In this context and following initial reports of high Curie temperature and contradictory reports on the magnetic states of this system, we investigated the diluted magnetic semiconductor Zn1-xCoxO. An ab initio study of structural, electronic and magnetic properties of Zn1-xCoxO was performed using the pseudopotentials method within the framework of density functional theory (DFT) with both GGA and GGA+U approximations. In parallel, thin films of Zn1-xCoxO were synthesised by reactive magnetron co-sputtering with different deposition conditions. The structural, morphological, electrical and magnetic properties were analyzed by various characterization techniques and compared with those obtained by ab inito study.

This work targeted the growth of gadolinium (Gd)-doped gallium nitride (GaN) thin films (Ga₁₋ₓGdₓN) by metal organic chemical vapor deposition (MOCVD). Characterization and evaluation of these Ga₁₋ₓGdₓN thin films for application in spintronics/optoelectronics devices also formed part of this work. This work presents: (1) the first report of stable, reproducible n- and p-type Ga₁₋ₓGdₓN thin films by MOCVD; (2) the first Ga₁₋ₓGdₓN p-n diode structure; and (3) the first report of a room temperature spin-polarized LED using a Ga₁₋ₓGdₓN spin injection layer. The Ga₁₋ₓGdₓN thin films grown in this work were electrically conductive, and co-doping them with Silicon (Si) or Magnesium (Mg) resulted in n-type and p-type materials, respectively. All the materials and structures grown in this work, including the Ga₁₋ₓGdₓN-based p-n diode and spin polarized LED, were characterized for their structural, optical, electrical and magnetic properties. The spin-polarized LED gave spin polarization ratio of 22% and systematic variation of this ratio at room temperature with external magnetic field was observed.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho abordamos algumas propriedades físicas associadas ao transporte spintrônico de nanoestruturas formadas por camadas de semicondutor diluído magnético (SDM) e semicondutor convencional submetidas a campos elétrico e magnético cruzados. O campo elétrico é aplicado na direção de crescimento da nanoestrutura e o campo magnético é aplicado perpendicularmente a essa direção. Estuda mos duas configurações de nanoestruturas onde o SDM localiza-se no poço quântico ou nas barreiras. Mostramos que é possível encontrar um potencial efetivo tipo poço de potencial duplo para um intervalo de intensidades de campos externos, altura da barreira de potencial e largura de poço quântico parabólico. Em tal condição esse sistema pode ser visto como um dispositivo spintrônico chamado filtro de spin, pois consegue selecionar polarizações de spin em diferentes regiões da nanoestrutura. / In the present work we studied properties of the spintronic transport of nanostructures formed by layers of diluted magnetic semiconductors (DMS) and conventional semiconductors with crossed fields applied. The electric field is in the growth direction and the magnetic field is perpendicular t o this one. We studied two configurations of nanostructures where the DMS is located in the barriers or in the well. We will show the possibility of the formation of a double quantum well like effective potential for different values of the applied fields intensities, barriers height and quantum well width. In this situation the system can be seen as a spintronic device called spin filter, since it can control the spin polarization in different regions of the nanostructure.

Made available in DSpace on 2016-06-02T20:16:47Z (GMT). No. of bitstreams: 1 3100.pdf: 15486082 bytes, checksum: 5571e424d9aa0ed6b176f29ef78c25dc (MD5) Previous issue date: 2010-05-07 / Universidade Federal de Sao Carlos / In this work, we have studied spin polarization of carriers in a resonant tunneling diode GaAs/AlGaAs with InAs quantum dots in the center of the quantum well. We have observed that the photoluminescence of quantum dots depends on applied voltage and light intensity. Our results were explained by the capture of minority carriers (holes) to quantum dot energy levels in the resonant conditions. We have also studied the polarized resolved photoluminescence under magnetic field applied parallel to the tunnel current. We have observed that the degree of circular polarization is voltage-dependent under low voltage and laser intensity condition. We have also observed that the degree of polarization of quantum dots tends to zero for high applied voltages. Our results show that the circular polarization depends on the injection and capture of holes by quantum dots. Finally, we observed that the circular polarization from quantum dots can be voltage and light-controlled and could be interesting for the developing of new spintronics devices. / Neste trabalho realizamos um estudo detalhado de efeitos de spin em um diodo de tunelamento ressonante GaAs/AlGaAs do tipo n com pontos quânticos de InAs no poço quântico. Os estudos foram realizados a partir de medidas elétricas e ópticas na presença e ausência de campo magnético. Os resultados obtidos na ausência de campo magnético são semelhantes aos resultados publicados na literatura para mesma amostra estudada. Em particular, obtivemos uma boa correlação entre a intensidade de luminescência dos quantum dots e a curva característica corrente - tensão (I(V)) do diodo. Os dados obtidos foram associados aos processos de tunelamento, relaxação e captura de portadores nos níveis de energia dos dots. As medidas realizadas na presença de campo magnético foram feitas da configuração de campo magnético paralelo à corrente elétrica no dispositivo. Tal disposição leva à quebra na degenerescência dos níveis em spin dos dots, e resulta em recombinação de portadores com regras de seleção bem definidas com luz circularmente polarizada. Observamos que tanto a emissão circularmente polarizada à esquerda como à direita são dependentes da tensão aplicada no diodo, principalmente na região de baixas voltagens. À medida que a tensão aumenta, a intensidade de polarização tende a zero. Os resultados obtidos são originais e devem auxiliar na compreensão de fenômenos de spin desses sistemas. Esse trabalho poderá também ter interesse no desenvolvimento de possíveis dispositivos de spintronica contendo pontos quânticos.

Made available in DSpace on 2016-06-02T20:16:48Z (GMT). No. of bitstreams: 1 3888.pdf: 18962527 bytes, checksum: f175880c3d28fb0f29001b9881fedf3e (MD5) Previous issue date: 2011-03-15 / Financiadora de Estudos e Projetos / In this work, we have studied the spin polarization of carriers in n-type resonant tunneling diodes (RTDs) of GaAs/AlGaAs which incorporates a single layer of InAs selfassembled quantum dots in the center of the GaAs quantum well (QW) grown on (3 1 1)B oriented GaAs substrates.We have performed electrical and optical measurements in the presence and absence of magnetic _eld. The spin-dependent carrier transport in the structure was investigated by measuring the left- and right-circularly polarized photoluminescence (PL) from InAs dots (QD) and contact layers as a function of the applied voltage, laser intensity and magnetic _eld up to 15 T. Under laser excitation, photogenerated holes tunnel through the QW and can be captured by the QDs and eventually recombine radiatively. Due to this fast carrier capture process, the QD photoluminescence will be very sensitive to the resonant tunneling condition and consequently to the applied bias voltage. We have observed a clear correlation between the current voltage characteristics curve (I(V)) and QD PL intensity for both circular _+ and _�� polarizations even though the spin-splitting of the QD PL emission is negligible and does not show any appreciable variation with the applied voltage. We have also observed that the QD circular polarization degree is always negative and that its value depends on both the applied bias voltage and the light excitation intensity. Our experimental results are explained by the tunneling of minority carriers into the QW, carrier capture into the InAs QDs, carrier accumulation in the QW region, and partial thermalization of minority carriers. The observed control of spin polarization of carriers by light and bias voltage may be explored to design new devices for spintronic applications. / Neste trabalho realizamos um estudo detalhado de efeitos de spin em um diodo tunelamento ressonante (RTD) de GaAs/AlGaAs crescidos em um substrato GaAs (311)B. Em particular estudamos RTDs do tipo n contendo pontos quânticos (QD) de InAs no poço quântico (QW). Os estudos foram realizados a partir de medidas elétricas e ópticas na presença e na ausência de campo magnético. Realizamos medidas de fotoluminescência (PL) resolvida em polarização do contato GaAs e pontos quânticos de InAs em função de intensidade de laser , voltagem e campo magnético de até 15T . Na presença de luz e voltagem aplicada , buracos são fotogerados no contato, tunelam para o QW e são capturados por QDs. Portadores capturados pelos QDs recombinam e dão origem ao sinal de fotoluminência. Devido ao tempo curto desse processo de captura de portadores, a PL do QD será muito sensível à condição de tunelamento ressonante. Os resultados experimentais mostram uma clara correlação entre a curva característica de corrente-tensão (I(V)) e intensidade de PL do QD para ambas polarizações _+ e _��. Observamos que o grau de polarização circular do QD é sempre negativo e que seu valor depende fortemente da voltagem aplicada e da intensidade da luz de excitação. Os resultados experimentais são explicados pelo tunelamento e captura de portadores minoritários pelo QD de InAs, acúmulo de cargas na região de QW e termalização parcial dos portadores minoritários. O controle da polarização de spin de portadores por luz e voltagem pode ser um efeito interessante para o desenvolvimento de novos dispositivos para aplicação em spintrônica.

Ce travail de thèse porte sur l'élaboration et la caractérisation de jonctions tunnel magnétiques (JTM) polycristallines à barrière d'oxyde de titane de strontium, SrTiO3, qui se situe parmi les nouvelles barrières tunnel aux bandes interdites les plus étroites, recensées par la littérature. De telles barrières pourraient répondre à un besoin applicatif crucial : avoir un produit résistance x surface, RA, plus faible dans les JTM, ou à son corollaire, avoir une épaisseur de barrière plus forte à RA égal tout en conservant une magnétorésistance tunnel, TMR, élevée. De précédents travaux ont montré que le SrTiO3 présente une température de cristallisation inhabituellement basse (< 400°C) lorsqu'il est déposé par pulvérisation par faisceau d'ions (IBS) ce qui peut le rendre compatible avec les électrodes magnétiques standards constitutives des JTM. Le dépôt par IBS restant une technique pour le moins exotique au regard de l'état de l'art des JTM, nous avons dans un premier temps élaboré des JTM à barrière d'oxyde de magnésium, MgO, matériau phare de la spintronique. Cette étude a permis de mettre en avant les paramètres spécifiques à cette technique de dépôt influant sur les propriétés de transport des JTM, notamment le type d'oxydation. Dans un second temps, nous avons réalisé des JTM CoFeB/SrTiO3/CoFeB par IBS à partir d'une cible céramique de SrTiO3, en nous inspirant du travail effectué sur le MgO. Les influences de plusieurs paramètres de dépôt, d'oxydation et de recuit ont été analysées, conduisant à deux tendances opposées avec des systèmes présentant soit à une TMR élevée (18 %), soit un RA faible (2.6 Ohm.µm²). Des JTM SrTiO3 ont ensuite été nanostructurées pour la première fois et les tests électriques ont montré que les JTM ayant un bas RA présentaient un comportement ohmique alors que celles ayant une TMR élevée présentaient le comportement tunnel attendu. De plus, ces dernières présentent un claquage diélectrique intrinsèque à l'oxyde. En parallèle, des études microstructurales ont montré une qualité morphologique des JTM SrTiO3 semblable à celle des JTM MgO à l'état de l'art. Toutefois, ces observations n'ont pas permis de statuer sur le caractère cristallisé ou non des barrières en SrTiO3. Plusieurs pistes visant à déterminer la température de cristallisation du SrTiO3 dans la gamme des épaisseurs extraordinairement faibles des barrières tunnel ont été proposées. / This work is focused on the development and the characterization of polycrystalline magnetic tunnel junctions (MTJ) with strontium titanium oxide barrier, SrTiO3, identified as a low band gap tunnel barrier by literature. Such barrier could fulfill the critical application requirement: having a lower resistance area product (RA) in MTJ, or its corollary, having a thicker barrier at constant RA, while keeping the tunnel magnetoresistance ratio (TMR) high enough. Former studies have shown that SrTiO3 deposited by ion beam sputtering (IBS) could crystallize at an unusual low temperature (< 400°C) which could make it compatible with the magnetic layers of MTJs. In a first place, MTJs with a tunnel barrier made of a well known material in spintronics, namely MgO, were deposited. This preliminary work allowed us to highlight the specific parameters affecting the transport properties in MTJs deposited by IBS, including the oxidation type. In a second place, CoFeB/SrTiO3/CoFeB MTJs were developed using IBS and a SrTiO3 ceramic target, learning from our experience on MgO based MTJs. Many combinations of different parameters (including deposition, oxidation and annealing parameters) were explored, leading to two opposite tendencies with systems having either a high TMR (up to 18 %) or a low RA (down to 2.6 Ohm.µm²). SrTiO3 based MTJs were then patterned for the first time and submitted to electrical tests. These tests showed that the MTJs having a low RA exhibited an ohmic behaviour while the MTJs having a large TMR showed the expected tunnel characteristics. Furthermore, the latter MTJs showed an intrinsic dielectric breakdown. In parallel, microstructural characterizations have shown that SrTiO3 based MTJs and MgO based MTJ were alike morphologically. Nevertheless, these observations alone were not enough to assess on the crystalline state of SrTiO3. Many possibilities/tracks aiming at determining the crystallisation temperature of SrTiO3, in the range of extremely low thicknesses used in MTJs, are identified.

Spintronique moléculaire : de la vanne de spin à la détection d'un spin unique. Parmi les thématiques qui ont émergé ces dix dernières années, la spintronique moléculaire est intéressante de par son caractère hybride, à la croisée entre l'électronique de spin, l'électronique moléculaire et le magnétisme moléculaire. Dans ce nouveau domaine, on cherche à exploiter les propriétés magnétiques et quantiques des aimants moléculaires pour créer des dispositifs originaux, utiles en spintronique ou en information quantique. Mon projet de thèse s'inscrit dans cette perspective en voulant combiner un transistor à nanotube de carbone avec des aimants à molécule unique, en les couplant par des interactions supramoléculaires. L'objectif est d'observer le renversement magnétique d'une seule molécule par des mesures de transport électronique à travers le nanotube. En effet, le diamètre de ce dernier étant comparable aux dimensions d'un aimant moléculaire, le couplage devrait être suffisamment fort pour en permettre la détection. La réalisation d'un tel dispositif, un défi technique, et la question de savoir s'il était réellement possible de détecter et de caractériser le moment d'une seule molécule ont constitué les deux enjeux majeurs de cette thèse. Une grande partie du travail réalisé porte sur la fabrication du dispositif expérimental par des techniques de micro- et nano-fabrication, ainsi que sur l'optimisation du greffage des aimants moléculaires sur la surface du nanotube. Dans un second temps, nous nous intéressons à l'étude du système et à son comportement à très basse température (100 mK). En effet, la proximité des aimants moléculaires TbPc2 modifie de façon spectaculaire les propriétés de transport d'un nanotube. En particulier, nous présentons la réalisation d'un dispositif dont la réponse est analogue à une vanne de spin classique, où les molécules magnétiques jouent le rôle de polariseur ou d'analyseur de spin. Grâce à ce système, nous avons réussi à affiner nos connaissances sur TbPc2. Entre autres résultats, nous sommes parvenus à isoler et à caractériser le retournement du moment magnétique d'un seul ion de terbium. Enfin, la dernière partie de cette thèse est consacrée à l'étude de l'interaction hyperfine au sein du terbium. En réalisant un dispositif qui n'est couplé qu'à deux molécules, nous avons mis en évidence qu'il est possible de réaliser une lecture directe de l'état d'un spin nucléaire unique. / Nowadays, new directions in quantum spintronics aim at transposing the existing concepts and at developing alternative ones with various types of materials, from inorganic to -conjugated organic semiconductors. In this context, single molecule-magnets (SMMs) are interesting candidates to be integrated in molecular spintronics devices. Such devices lead the way for the electronic detection and coherent manipulation of SMMs spin states, exploitable in quantum computation schemes. We developed for this purpose an innovative multi-terminals device based on a carbon nanotube quantum dot, laterally coupled to few SMMs through supramolecular interaction. The conductance of the nanotube is measured at very low temperature (40 mK) and each time one of the SMM magnetic moment reverses, the conductance changes. The latters act on the conduction electron through the QD as spin polarizer and analyzer. This spin-valve effect gives access to the behavior of a single localized spin by standard electrometry We report a full magnetic characterization of a single bis-phthalocyaninato terbium complex (TbPc2). In particular, we performed a detailed study of quantum tunnelling of the magnetization of the Tb electronic moment and we present a read-out technic of the Tb nuclear spin state. These results open up strong perspectives for a coherent manipulation of a single nuclear spin in TbPc2.

Cette thèse se situe à la croisée de trois domaines : la spintronique qui s'attache à utiliser le degré de liberté du spin de l'électron afin de fabriquer de nouveaux dispositifs électroniques; l'électronique moléculaire qui cherche à profiter des progrès de la chimie moderne afin de fournir des alternatives au tout semi-conducteur de la micro-électronique; le magnétisme moléculaire qui cherche à synthétiser des aimants moléculaires aux propriétés toujours plus riches. Notre travail a consisté à produire un dispositif électronique à base d'aimant moléculaire et d'utiliser le spin de l'électron afin d'étudier les propriétés magnétiques à l'échelle d'une molécule. Des dispositifs semblables pourraient, dans l'avenir, constituer l'une des briques élémentaires de l'information quantique. Nous avons pour cela opté pour un transistor moléculaire à effet de champ, ayant pour canal un aimant moléculaire aux propriétés magnétiques bien connues : le Terbium double-decker ou TbPc2. Grâce à ce dispositif, nous avons, dans un premier temps, mis en évidence le retournement de l'aimantation d'une molécule unique par effet tunnel ou QTM (quantum tunneling of the magnetization). En effet, nous avons démontré que ce retournement entraînait une modification soudaine de la conductance de notre système. En effectuant une étude statistique sur les valeurs du champ de retournement, nous avons mis en évidence la présence de résonances que nous avons pu attribuer au phénomène de QTM. Nous avons également mesuré l'état d'un spin nucléaire unique : chaque résonance étant associée à un état de spin nucléaire. Nous avons étudié la température du spin nucléaire et montré que celle-ci pouvait être influencée par l'environnement électrostatique du système. En outre, le temps de vie d'un état de spin nucléaire a été extrait et estimé à quelques secondes, vérifiant que le système était faiblement perturbé par notre technique de mesure. Ces travaux jettent les bases de la construction du premier Qbit à base d'aimants moléculaires. Par des techniques de radiofréquence, le spin nucléaire pourrait être manipulé, la lecture se faisant ensuite par une mesure en conductance. / This PhD thesis is at a cross-road between three different fields : the spintronics which uses the spin degree of freedom of the electron to build new devices ; the molecular electronics which tries to take advantage of the new development of the chemistry, to give a workaround to the all semiconductor paradigm of the microelectronics industry; and the molecular magnetism which synthesizes molecular magnet with properties of an increasing richness. Our work has been dedicated to the fabrication of a molecular magnet based electronic device with which we could use the spin of the electron to study the magnetic properties at a single molecule level. Such device could, in the future, be used in the field of quantum information. We have decided to fabricate a field effect molecular transistor in which a well known molecular magnet, the Terbium double-decker or TbPc2, acts as a channel. Thanks to this device, we evidenced the quantum tunnelling of the magnetization (QTM) at single molecule level. We demonstrated that the magnetic moment reversal induces an abrupt change in the differential conductance of the system. By performing a statistical study, we highlighted four resonances that were attributed to QTM. We also measured a single nuclear spin state : each resonance being directly associated with one particular nuclear spin state. We studied the nuclear spin temperature and showed that it could be influenced by the electrostatic environment. Furthermore, the spin state lifetime was assessed and estimated to few seconds, highlighting the low invasive character of our measurement technique. This work give the foundation of the first molecular magnet based Qbit. With radio frequency techniques, the nuclear spin could be manipulated, the readout being performed through conductance measurement.

Submitted by Alison Vanceto (alison-vanceto@hotmail.com) on 2017-05-22T12:58:51Z No. of bitstreams: 1 DissYJOR.pdf: 3749771 bytes, checksum: 98b6729837eaa69cb6eb598ad207cfcf (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-23T20:35:23Z (GMT) No. of bitstreams: 1 DissYJOR.pdf: 3749771 bytes, checksum: 98b6729837eaa69cb6eb598ad207cfcf (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-23T20:35:31Z (GMT) No. of bitstreams: 1 DissYJOR.pdf: 3749771 bytes, checksum: 98b6729837eaa69cb6eb598ad207cfcf (MD5) / Made available in DSpace on 2017-05-25T19:51:05Z (GMT). No. of bitstreams: 1 DissYJOR.pdf: 3749771 bytes, checksum: 98b6729837eaa69cb6eb598ad207cfcf (MD5) Previous issue date: 2016-03-09 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / We report a systematic study on the structural, morphological and optical properties of Zn1−xCoxO thin films grown by spray pyrolysis. The employed nominal concentrations were up to 15 Co %. The films were deposited on glass substrates between 220-300 o C using precursors such as zinc acetate and cobalt acetate in aqueous solutions. The effects of Co-doping on structural, morphological and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical transmittance and absorbance as well as photoluminescence (PL). The XRD results indicated that all films are polycrystalline with wurtzite crystal structure, a preferential growth direction in c-axis, and no secondary phases. SEM images generally showed uniform surface, and few regions have irregularities due to effects of the inclusion of cobalt as well as substrate deposition temperature. The spectra of transmittance and absorbance exhibited the transitions d-d due to Co2+ ion, a redshift of the absorption-edge and changes in the absorption band intensity with increasing of nominal Co-doping. These observations revealed the substitution of Zn ions Zn2+ and the presence of Co in the state 2+ in tetrahedral coordination in the ZnO lattice. Furthermore, there was a narrowing in band gap of 28 meV by percentage of Co inserted into the lattice. The PL spectra of ZnCoO samples presented three bands associated to near-band-edge absorption (NBE), structural defects and intratomic emissions of Co2+. Their optical emissions were characterized by the presence of traps which capture carriers and affect significantly the emissions. Through a qualitative model in a temperature range we interpreted these traps as potential fluctuations up to 17 meV. We also discussed the annealing in selected samples. / Apresentamos um estudo sistemático sobre as propriedades estruturais, morfológicas e ópticas de filmes Zn1−xCoxO com concentrações nominais de Co até 15% obtidos por spray pirólise. Os filmes foram depositados sobre substratos de vidro entre 220 - 300 oC, utilizando como precursores acetato de zinco e acetato de cobalto em solução aquosa. Os efeitos da dopagem com Co nas propriedades estruturais, morfológicas e ópticas foram estudados por difração de raios-X (DRX), microscopia eletrônica de varredura (MEV), transmitância e absorbância óptica, e fotoluminescência (PL). Os resultados de DRX indicaram que todos os filmes são policristalinos, com estrutura cristalina do tipo wurtzita e direção de crescimento preferencial no eixo c, com ausência de fases secundárias. As imagens do MEV, em geral, mostraram que as superfícies são uniformes, com irregularidades em algumas regiões devido aos efeitos da inserção de Cobalto e da temperatura de deposição do substrato. Nos espectros de transmitância e absorbância, observaram-se a presença das transições d-d do íon de Co2+, o deslocamento da borda de absorção para baixas energias, e a variação da intensidade da banda de absorção das transições d-d com o aumento da dopagem nominal de Co. Estas observações revelaram a substituição dos íons de Zn2+ e a presença de Co no estado +2 na coordenação tetraédrica na rede do ZnO. Além disso, houve uma redução da energia do bandgap de 28 meV por porcentagem de Co inserido na rede. Os espectros de PL das amostras de ZnO dopado com Co apresentaram três bandas associadas à emissão próxima à borda de absorção óptica, defeitos estruturais e emissão intratômica do Co2+. A emissão óptica dos filmes foi caracterizada pela presença de armadilhas que localizam os portadores de carga e afetam significativamente as bandas de emissão no intervalo de temperatura estudado. Através de um modelo qualitativo interpretamos estas armadilhas como flutuações de potencial com profundidades de até 17 meV. Discutimos também o tratamento térmico em amostras selecionadas.