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In this research, the contents are divided into two sections. In the first section, we investigated carrier transport behavior of organic optoelectronic devices by using space charge limited current(SCLC) method. Firstly, we fabricated a hole-only device (ITO/Spiro-MeOTAD/Al) for Sprio-MeOTAD and the current density¡V voltage(J-V) characteristics of the device was measured. The J-V characteristics of the device do not match with SCLCs very well at high voltage since the number of hole injection was not enough to achieve SCLCs condition. To enhance the injection of hole carrier into the organic layer, a MoO3 buffer layer was inserted between ITO electrode and organic layer. The current density in device with MoO3 buffer layer achieved 5 times enhancement, indicating that the concentration of hole in MoO3 device is increment. Hence, we succeeded in making the J-V characteristics of the hole-only device to match with SCLCs well at high voltage, and the hole mobility of Sprio-MeOTAD estimated by SCLCs was 1.44¡Ñ10-4cm2/Vs. Li salt was also doped into Sprio-MeOTAD as an n-type dopant. We found that Li salt could form hole-traps in Sprio-MeOTAD, which reduced hole carriers in Spiro-MeOTAD. The current density of the device was decreased, and the device could not achieve SCLCs condition at high voltage. In the second section, we use two novel iridium(Ir) complexes to fabricate blue-green emitting devices by solution process. First, we obtained optimum concentration of phosphorescent emitters by controlling of the dopants concentration. Then, we adjusted the thickness of the electron injection layer, hole injection layer, and emission layer to design more suitable device structure. Finally, we succeeded in fabricating blue-green light emitting devices. The maxima luminescence was 37.7cd/m2 and maxima current efficiency was 1.68 cd/A in the Ir complex based devices.

With the progress of technology, large capacity and scalable are required for the future. Recent years, the physical limit is approached and a next-generation memory is needed in the future. In addition, non- volatile memory occupies more than 96% in the memory market, and RRAM has great advantages such as simple structure, high scalable, low operation voltage, high operation speed, high endurance and retention. That is the reason RRAM is the candidate in the next generation. In this experiment, multi-sputtering was used to deposit Zr:SiO 2 and Pt on TiN bottom electrode. The sandwich structure was metal/insulator/metal (MIM). With the different dielectric constant material, a different electrical field will be produced. And then I-V measurement and materials analysis were used to investigate the characteristic of the RRAM. At first, a forming process is required to the RRAM. The device was swept from negative to positive voltage and obtained the conduction mechanism from curve fitting. The different dielectric constant materials were used to fabricate the RRAM. High and low dielectric materials were HfO 2 and BN, respectively. The electric field distribution is centralized in low dielectric material so the electrons will drift to the direction of electric field. Hence, the Vset will be centralized and more stable. We also fabricated a Zr:SiO 2 /C:SiO 2 RRAM as an high K and low K material. The current fitting results that a hopping conduction occurs in low resistive state (LRS) and high resistive state (HRS). Both from Raman spectrum and FT-IR spectrum, a graphene oxide was existed in the C:SiO 2 thin film. While the filament was form, the tip of the filament will approach the graphene oxide because of the point effect. Hence, the resistance switching will happen in the grapheme oxide and set voltage will be more stable and lower the operated current. Next, an ICP treatment was used in order to "burn" the carbon in SiO 2 . The purpose is to make an extremely low K material and ignore the effect of the existence of carbon. From the FT-IR spectrum, the carbon signals were disappeared after the ICP oxygen plasma treatment. In the I-V fitting diagram, space char limit results in the high voltage region. The electrical field simulation was an auxiliary tool which shows a strong electrical field occurs in the extremely low K area. While the electrons flow through the conduction path, they will be confined in the porous area. The operation current will decrease because of the limited conduction area.

Organic semiconductors are very attractive for thin film Organic Photodetectors (OPDs) since they possess a number of desirable attributes for optical sensing including high absorption coefficients over visible and ultraviolet wavelengths and compatibility with large-area deposition processes such as ink-jet, screen printing, and solution processing. OPDs, in general, utilize a vertical device architecture where the photoactive organic semiconductor layers are sandwiched between top and bottom electrodes that provide electrical contact. More recently, an interest in utilizing a lateral device architecture instead of the vertical one, has emerged. In this architecture, the two contacts are positioned on the two sides of the photoactive material with respect to the direction of the incoming signal, separated by a small gap. However, the factors governing lateral OPDs’ photo-response are still not well understood. In this thesis, we fabricate top-contact lateral OPDs using a thermal evaporation only fabrication process. We study the factors governing both the dark and photo currents of lateral OPDs. The effect of the wide gap between the two electrodes on the current-voltage characteristics is discussed and the role of space charge limited conduction is investigated. The contributions in the photoresponse of light scattering through the active layers as well as the back reflection of light at the metallic contacts are emphasized. The reproducibility over repeated operation cycles of both dark and photo currents values is explored. Exposure to light of the lateral OPD is found to lead to a significant increase in the dark current. The role of the conductivity enhancement in the channel due to light-induced trap filling is investigated. External quantum efficiency and detectivity estimates are given for deep ultraviolet lateral (DUV) OPDs. A comparison with vertical DUV OPDs performances is provided. Finally, the use of a phosphorescent sensitizer doped in the absorbing bottom layer to improve top-contact lateral OPDs efficiency is discussed.

2012 IEEE International Symposium on Electrical Insulation (ISEI), June 10-13, 2012, Ritz Carlton Hotel, San Juan, PR, USA

GaSe thin films were deposited by thermal evaporation technique with and without Cd doping. X-ray analysis showed that the crystallinity increases in (1014) preferred orientation direction with annealing for doped and undoped films. The room temperature conductivity and mobility values of the samples were found to be for doped and undoped films in between 1.3&times / 101 - 3.4&times / 102 (&amp / #8486 / -cm)-1, 1.2&times / 10-6 - 1.5&times / 10-6 (&amp / #8486 / -cm)-1 and 5.9 &amp / #8211 / 20.9 (cm2/V.s) (for doped samples only), respectively. Due to the high resistivity of the undoped samples mobility measurements could not be performed. The dominant conduction mechanisms were determined to be thermionic emission in the high temperature region (250-400 K), tunneling in the range 160-250 K and between 100-150 K variable range hopping mechanism for the doped films. For the undoped films above 250 K thermionic emission was the dominant conduction mechanism. Space charge limited currents in parallel and perpendicular directions of the film surface showed two different localized energy levels with different concentrations for each case, namely, 99.8 meV with concentration 3.5&times / 1012 cm-3 and 418.3 meV with the concentration 2.2&times / 105 cm-3 for parallel direction and for perpendicular direction 58.3 meV with concentration 6.2&times / 1025 cm-3 and 486.1 meV with concentration 3.3&times / 1022 cm-3. Photocurrentillumination intensity dependences indicated that power exponent of illumination intensity with values n&gt / 1 implied two recombination centers exist in studied samples.

Title: Photoconductivity, photoluminescence and charge collection in semiinsulating CdTe and CdZnTe Author: Jakub Zázvorka Department: Institute of Physics of Charles University Supervisor of the doctoral thesis: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles University. Abstract: Cadmium telluride and its compounds with zinc are the material of choice in spectroscopic room temperature high energy radiation detectors. The development of the final device is influenced by many parameters, including material impurities and defects, homogeneity and surface preparation. This thesis offers a comprehensive investigation of the detector fabrication process and of the parameters and physical effects influencing the spectroscopic resolution and performance of the detector. Structure of deep levels is investigated through photoluminescence and correlated with other electro-optical measurements dealing with the impact of structural imperfections of the material and their effect. The influence of resistivity and photoconductivity homogeneity on the detector performance is studied through electrical measurement of the charge carrier transport and charge collection of the sample. Obtained results are explained using the Fermi level shift theory and confronted with a theoretical model and calculations. The...

Pre-breakdown phenomena in transformer liquids have been extensively investigated. The published work can be broadly categorised into streamer and partial discharge (PD) studies, with the former focusing on physical nature and the latter being more relevant to industrial applications. Mineral oil, as the dominant candidate, has been used in power transformers for over a century. In the past decade, there has been an increasing interest in filling power transformers with alternative liquids, e.g. esters and gas-to-liquids (GTL) based oils. This work aims to correlate the PD and streamer characteristics of three transformer liquids under AC stress. The liquids include a conventional mineral oil (Gemini X), a GTL oil (Diala S4 ZX-I) and a synthetic ester (MIDEL 7131). A circuit arrangement in compliance with the IEC 60270 was used, which allowed PD measurements, wide-band current measurements and streamer shadowgraphs to be obtained simultaneously. To simulate the quasi-uniform electric fields in transformers, a plane-to-plane electrode system incorporating an adjustable needle protrusion (PNP) was employed. A needle-to-plane electrode system (NP), which is widely used in the field, was also employed to provide reference results. Based on the PD measurement results, the PD inception fields (PDIFs) of the three liquids were found to be independent of electrode geometry for the investigated tip radius. The PDIF of the synthetic ester is about 13% lower than that of the mineral oil or the GTL oil. Compared with the PD magnitude, the pulse repetition rate is more sensitive to liquid type. At the same voltage under both the NP and PNP configurations, the synthetic ester has the highest pulse repetition rate, followed by the GTL oil, and then the mineral oil. In divergent electric fields (provided by the NP electrode system), it was found that the streamers in the three liquids have a similar stopping length at the same voltage, even though the apparent charge readings are not the same. The correlations between PD and streamer characteristics indicated that the synthetic ester has the highest branching tendency, and has therefore the smallest stopping length per unit of apparent charge among the three liquids. In quasi-uniform electric fields (provided by the PNP electrode system), the streamer branching tendencies of the three liquids were largely suppressed. The change from a propagation-induced breakdown in divergent fields to an initiation-induced breakdown in quasi-uniform fields was explained. The correlations between PD and streamer characteristics revealed that the same apparent charge can indicate different levels of streamer development in the insulation, depending on the uniformity of the electric field. Overall, interpreting PD measurement results needs to take the electric field uniformity (PD location) as well as liquid type into consideration.

L’objet de ce travail de thèse est l’étude du polyéthylène réticulé chimiquement (PRC) utilisé pour les câbles haute tension à courant continu (HTCC). Les propriétés électriques du PRC ont été largement étudiées en alternatif mais sont moins bien connues dans le cadre d’une contrainte continue. Une meilleure compréhension des propriétés diélectriques et de la durée de vie pourraient permettre aux fabricants et utilisateurs de proposer des tests de qualification et s’assurer du bon fonctionnement des systèmes de câble durant leur exploitation.Ces travaux présentent les câbles utilisés pour le transport HTCC ainsi que les contraintes physiques et chimiques endurées par le PRC en service. Le PRC est issu de la réaction de réticulation du polyéthylène basse densité (LDPE) amorcée par le peroxyde dicumylique. Il en résulte la présence de sous-produits, dont la majorité est évacuée par un traitement de dégazage du câble. Un additif antioxydant est par ailleurs ajouté à l’isolant du câble pour protéger le PRC durant la production puis l’exploitation du câble. Les contraintes appliquées au câble peuvent influencer les propriétés diélectriques. Notamment, la présence de charges électriques piégées (ou charges d’espace) peuvent influencer la durée de vie de l’isolant.Les propriétés d’injection/conduction, les mécanismes de pertes, la rigidité électrique, la charge d’espace et des propriétés chimiques de plaques circulaires de XLPE munies d’électrodes semiconductrices ont été étudiées. Sous l’effet des contraintes thermoélectriques, des charges électriques peuvent acquérir assez d’énergie pour être injectées dans l’isolant, selon différents mécanismes possibles, puis traverser l’isolant jusqu’à atteindre l’électrode opposée selon, là aussi, différents mécanismes. Selon le champ électrique appliqué, le mécanisme d’injection dominant est l’effet Schottky et le mécanisme de transport est le courant limité par charge d’espace (usuellement appelé SCLC). En ce qui concerne les mécanismes de pertes, à faible fréquence, le mécanisme de conduction quasi DC a été identifié à température ambiante tandis qu’à 70, 80 et 90°C, la conduction DC a été mise en évidence. De plus, les pertes augmentent lorsque la température d’étude augmente. La rigidité diélectrique a été déterminée à l’aide d’un panel d’échantillons. Sa valeur, déterminée par la loi de Weibull est de 375 kV/mm à température ambiante. La charge d’espace a été étudiée en utilisant la méthode de l’onde thermique (MOT). Ces analyses ont montré deux types de charges dominantes dans le matériau : homocharge et hétérocharge. La prédominance d’un type de charge par rapport à un autre est influencée par le champ électrique et la température. Le champ électrique total (addition du champ électrique dû à la charge d’espace et avec le champ électrique appliqué) atteint jusqu’à 100 kV/mm en appliquant 60 kV.mm. Les caractérisations chimiques ont montré une température de fusion de 103°C et une cristallinité de 39 %. Avant l’application de contraintes, l’index carbonyle, indiquant la présence de liaisons carbonyles est de 0,5.L’impact de contraintes thermoélectriques sur les propriétés diélectriques du PRC a été étudié à 70, 80 et 90°C sous 30 et 60 kV/mm. Des augmentations de la capacité et du facteur de pertes ont été observées et pourraient être assignées à la consommation presque totale de l’antioxydant à 90°C quelle que soit la contrainte électrique. La charge d’espace a elle aussi montré des évolutions significatives. Des différences ont été observées en fonction de la température, du champ électrique et du temps de vieillissement. Ces résultats ont été utilisés pour proposer une cinématique de vieillissement prenant en compte la charge d’espace et basé sur la consommation d’antioxydant menant à la croissance d’une couche de PRC oxydé contenant de nouvelles liaisons carbonyles comme le montre l’évolution de l’index de carbonyles. / The present work concerns the study of the cross-linked polyethylene (XLPE) used for high voltage direct current (HVDC) cable insulation. The electrical properties of XLPE have been widely studied under AC stress, however the behaviour of these materials under high DC stress is less known and needs thorough investigation. The insulation should be better understood in terms of dielectric behaviour and lifetime. A better knowledge of HVDC insulation could allow manufacturers, utilities and TSO’s to propose a relevant qualification processes and to ensure that cable systems will remain safe and operational during their entire lifetime.This work introduces HVDC cables and especially the physical and chemical stresses assumed by the cross linked polyethylene (XLPE) insulation due to operational conditions. XLPE insulation is the result of the reticulation of low density polyethylene (LDPE), obtained with the decomposition of the cumyl peroxide. It causes the presence of byproducts in the insulation. The cables, degassed in order to extract these byproducts contains antioxidant agents, protecting the insulation during the production of HVDC cables and during the exploitation. The stresses can influence the insulation dielectric properties. As example, the presence of electric charges could influence the lifetime of the insulation.The injection/conduction, loss mechanisms, dielectric rigidity, space charge and chemical properties have been investigated at initial state. Under thermal and electric stresses, charges can reach the injection energy according with different mechanisms. Then, charges can be carrier to the opposite electrode with different mechanisms. Dominant mechanisms have been identified: Schottky injection and Space Charge Limited Current (SCLC) conduction, according with applied electric field. Concerning loss mechanisms, the low frequency mechanisms are nearly DC conduction at room temperature and DC conduction for higher temperatures. Moreover, the dielectric loss factor increases when temperature increases. The dielectric rigidity has been measured with Weibull’s law on a panel of 12 samples. The value of this property is 375 kV/mm, at room temperature. The space charges have been measured using the Thermal Step Method (TSM). These analyses show that two types of charge are present in the material (homocharge and heterocharge). This effect is influenced by temperature and electric field. The total electric field (addition of the applied electric field and electric field due to space charge) reaches until 100 kV/mm whereas 60 kV/mm is applied. Concerning the chemical properties of XLPE samples, the melting point has been measured at 103°C and the crystallinity is about 39 %. Before ageing stresses, the carbonyl index is worth 0.5 due to the slight presence of carbonyl bonds.The impact of a combined electric and thermal stress on dielectric properties is studied at 70, 80 and 90°C under 30 and 60 kV/mm. Increases of capacitance and loss factor possibly linked to the nearly total consumption of the antioxidant have been observed at 90°C for each electrical stress. Space charge analysis has shown significant variations. Differences have been observed as a function of ageing test temperature, applied electric field stress and ageing time. These results have been used to propose an ageing mechanism taking into account the development of space charges and based on the consumption of the antioxidant leading to the grow of an XLPE oxidised coat containing new carbonyl bonds as indicated by the carbonyl index after 857 days under stresses.

A finalidade principal deste trabalho é o da obtenção de soluções numéricas de movimento de carga espacial livre em que as grandezas pertinentes dependem de mais de uma coordenada espacial (casos não unidimensionais). Mais especificamente, os problemas estudados versam sobre casos em que um eletródio plano a um dado potencial emite carga não uniformemente ao longo de sua extensão e procura-se obter a deformação das linhas de campo daí resultantes, no espaço até um outro eletródio aterrado disposto paralelamente ao primeiro. Um método baseado em soluções tentativas bem como um outro global usando a \"transformação hodográfica\" recentemente formulada por Budd e Wheeler são apresentados. E também realizado um estudo breve sobre a validade da muito empregada \"suposição de Deutsch\" / The aim of the present work is to obtain numerical solutions of free space charge motion in cases in which the pertinent quantites depend on more than one space coordinate (non uni-dimensional cases). More specifically, the problems under concern here are those in which a plane electrode, at a constant potential, emit charge in a non-uniform way along them and the resultant deformation of the field lines, in the space between it and another plane grounded electrode parallelly disposed, is looked for. A method based on guessed solutions and also a global one using the hodographic transformation recently developed by Budd and Wheeler are presented. A brief study of the validity of the often employed \"Deutsch assumption\" is also carried out