Trapping centres and their distributions in as-grown TlGaSeS layered single crystals were studied using thermally stimulated current (TSC) measurements. The investigations were performed in the temperature range of 10&ndash / 160 K with various heating rates between 0.6&ndash / 1.2 K/s. Experimental evidence has been found for the presence of three electrons trapping centres with activation energies 12, 20, and 49 meV and one hole trapping centre located at 12 meV. Their capture cross-sections and concentrations were also determined. It is concluded that in these centres retrapping is negligible as confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. The optical properties of TlGaSeS layered single crystals have been investigated by measuring the transmission and the reflection in the wavelength region between 400 and 1100 nm. The optical indirect transitions with a band gap energy of 2.27 eV and direct transitions with a band gap energy of 2.58 eV were found by analyzing the absorption data at room temperature. The rate of change v of the indirect band gap with temperature was determined from the transmission measurements in the temperature range of 10&ndash / 300 K. The oscillator and the dispersion energies, the oscillator strength, and the zero-frequency refractive index were also reported. The parameters of monoclinic unit cell and the chemical composition of TlGaSes crystals were found by X-ray powder diffraction and energy dispersive spectroscopic analysis, respectively.

Ametistas naturais brasileiras foram estudadas através das técnicas de Absorção Óptica (AO), Ressonância Paramagnética Eletrônica (RPE) e Corrente de Despolarização Termicamente Estimulada (CDTE).O espectro de AO apresentou três picos principais na região espectral do visível (10500, 18600 e 28200cm POT.-1) e um enorme pico na região do ultravioleta (45000cm POT.-1) atribuídos ao ferro em diferentes estados de valência. A presença de centros OH POT.- foi observada na região do infravermelho através das bandas em 3440 e 3580cm POT.-1. O espectro de RPE, operando na banda X, exibe um conjunto de linhas centrado em 2000G, um pico intenso em 3000G e quatro picos pequenos em 4000, 5000, 6000 e 7000G, quando o campo magnético encontra-se paralelo a um dos eixos cristalograficamente equivalentes. Quando o campo magnético encontra-se paralelo ao eixo c do cristal, o espectro de RPE revela um conjunto de linhas centrado em 2000G, dois picos intensos próximos a 5000G e um pico pequeno em 6800G. Amostras em pó apresentam uma banda larga centrada em 3400G. Tratamentos térmicos mostram uma redução gradativa desta banda com o aumento do tempo de tratamento térmico e uma redução mais rápida para temperaturas maiores. Sabe-se que os centros de cor nas ametistas são produzidos pela ação de radiação ionizante natural sobre os centros precursores que surgem da substituição do Si POT.4+ pelo Fe POT.3+ na estrutura do quartzo-alfa. Esses centros de Fe POT.3+ não se distribuem igualmente entre os sítios equivalentes no cristal natural e são responsáveis pelas características dominantes do espectro de RPE. O espectro de CDTE obtido da polarização de uma amostra em 1000V apresenta uma banda em 215K, que vem a ser a composição de três bandas de menor intensidade (185, 200 e 214K) e uma banda única em 260K. Foi confirmado o caráter dipolar dessas bandas. Tratamentos térmicos efetuados a diferentes temperaturas mostram ) um decaimento de área total e uma redução da intensidade das bandas mais acentuadas para temperaturas maiores. Iluminação ultravioleta restaura parcialmente o espectro de CDTE e demonstra o crescimento de uma banda na região da temperatura ambiente. Devido ao comportamento semelhante dos espectros de CDTE e de RPE, o sendo Fe POT.3+ um elemento presente em grande quantidade nas amostras estudadas, acredita-se que o centro de dipolo responsável pelas bandas de CDTE observadas, seja do Fe POT.3+ substituindo um Si POT.4+ próximo a um O POT.- ou a um OH POT.-, e que as diferentes posições dos picos devem-se à população desigual do Fe POT.3+ substitucional nos sítios cristalograficamente equivalentes do cristal. / Brazilian natural amethyst samples have been studied through Optical Absorption (AO), Electron Paramagnetic Resonance (EPR) and Thermally Stimulated Depolarization Current (TSDC) Techniques.The AO spectrum shows three main peaks in the visible region (10500, 18600 e 28200cm POT.-1) and a huge peak in the ultraviolet region (45000cm POT.-1). All these peaks were attributed to iron in different valence states. The presence of centros OH POT.- centres have been observed through the bands at 3440 e 3580cm POT.-1in the infrared.The EPR spectrum shows a set of lines centered at 2000G, an intense peak at 3000G and four small peaks at 4000, 5000, 6000 and 7000G, when the magnetic field is parallel to one of crystallographically equivalents sites. When the magnetic field is parallel to the crystal c-axis, the EPR spectrum shows a set of lines centered at 2000G, two high peaks near 5000G and a small peak at 6800G. Powder samples presents a broad band centered in 3400G. Thermal treatments reduce this band for increasing thermal treatments time intervals. The reduction increases for high temperatures. It is well known that colour centres in amethysts are produced after natural ionizing radiation and that the centres are provided with the substitution of Fe POT.3+ for Si POT.4+ in quartzo-alfa structure. The Fe POT.3+ centres are not equally distributed among the equivalent sites of the natural crystal and are responsible for the dominant features of the EPR spectra. The obtained TSDC spectrum for polarization at 1000V shows a broad band at 215K, resulting from the superposition of three bands at 185, 200 and 214k and another band at 260K. The dipole origin of these bands has been confirmed. Thermal treatments at different temperatures produce a decay of the total area and a reduction of the bands intensities. Thermal reduction increases for higher temperatures. Ultraviolet illumination partially restores the TSDC spectrum. A new band appears at room temperature. Due to the similar behavior of the TSDC and EPR spectra and taking into account that the Fe POT.3+ is the most prominent impurity in the studied samples, we believe that the dipoles are substitutional Fe POT.3+ near O POT.- or an OH POT.- and that the different position of the peaks, very near, but not the same, are in crystallographically equivalent sites.

Esta dissertação poderia ser dividida em duas partes, sem que houvesse prejuízo para o seu entedimento: uma tratando do topázio natural (Al IND.2 SiO IND.4[F, OH] IND.2) e outra, a respeito dos vidros silicatos tipo soda-lime (SiO IND.2+CaO+Na IND.2 O). Em ambas se procura contribuir para o estudo de defeitos com algumas técnicas experimentais, mais enfaticamente as correntes de despolarização termicamente estimuladas (CDTE). Com relação ao topázio, há diversos estudos tratando de sua termoluminescência (TL) e de possíveis aplicações no que tange ao seu emprego como dosímetro termoluminescente. Procuramos complementar esses resultados com medidas de CDTE, técnica que ainda não havia sido utilizada para este material. Localizamos no topázio três bandas de CDTE, porém os resultados não são conclusivos no que se refere às origens dessas bandas. Em parte porque temos consciência de que os resultados variam bastante quando se estudam amostras naturais, com composições que variam dentro de um mesmo pedaço de cristal. No que diz respeito aos vidros soda-lime, o estudo foi mais abrangente. Há várias trabalhos no sentido de se conhecer melhor os efeitos causados pela irradiação de vidros silicatos. Acredita-se que o sódio desempenhe um papel fundamental nas principais mudanças processadas nesse material após irradiação gama. Assim, este estudo procurou comparar os resultados de TL e CDTE, além de absorção óptica, de vidros soda-lime com diferentes concentrações de Na POT.+ e K POT.+. Ao que tudo indica os processos responsáveis pela TL e CDTE dependem da relação entre as concentrações desses íons. Verificaram-se também variações com a taxa de dose, e os efeitos de tratamentos térmicos para situações onde um ou outro íon prevalece. / This work could be split in two different parts without impairment understanding. One of them, on natural topaz (Al2SiOdF,OH] 2) and the other on soda-lime silicate (SLS) glasses (Si02 + CaO + Na20) . In both of them we intend to contribute with more information on their defect composition, using some experimental techniques, especially the so called thermally stimulated depolarization currents (TSDC) . There are many surveys on topaz thermoluminescence (TL) and the possibility of its use as a TL dosimeter. So, one of the purposes of this study was to make a contribution with a technique not used so far with such material. We have detected three TSDC peaks. The results are not conclusive about the origin of those peaks, in part because we are dealing with a natural material whose composition can vary even within the same piece of crystal. As the SLS glasses, the study was more comprehensive. There are plenty of papers on irradiation effects in silicate glasses and attempts to understand the mechanisms responsible for them. It is believed that sodium plays a fundamental role in the main modifications caused by gamma irradiation of these glasses. In addition, this study attempts to compare the TL and TSDC results in SLS glasses with different concentrations of Na+ and K+. From our observations, the processes responsible for both TL and TSCD peaks depend on the relative concentrations of those ions. Furthermore, variations on the signals were also noticed; depending on the irradiation rate and on the thermal treatments performed, in samples where one or another ion prevails.

Esta dissertação poderia ser dividida em duas partes, sem que houvesse prejuízo para o seu entedimento: uma tratando do topázio natural (Al IND.2 SiO IND.4[F, OH] IND.2) e outra, a respeito dos vidros silicatos tipo soda-lime (SiO IND.2+CaO+Na IND.2 O). Em ambas se procura contribuir para o estudo de defeitos com algumas técnicas experimentais, mais enfaticamente as correntes de despolarização termicamente estimuladas (CDTE). Com relação ao topázio, há diversos estudos tratando de sua termoluminescência (TL) e de possíveis aplicações no que tange ao seu emprego como dosímetro termoluminescente. Procuramos complementar esses resultados com medidas de CDTE, técnica que ainda não havia sido utilizada para este material. Localizamos no topázio três bandas de CDTE, porém os resultados não são conclusivos no que se refere às origens dessas bandas. Em parte porque temos consciência de que os resultados variam bastante quando se estudam amostras naturais, com composições que variam dentro de um mesmo pedaço de cristal. No que diz respeito aos vidros soda-lime, o estudo foi mais abrangente. Há várias trabalhos no sentido de se conhecer melhor os efeitos causados pela irradiação de vidros silicatos. Acredita-se que o sódio desempenhe um papel fundamental nas principais mudanças processadas nesse material após irradiação gama. Assim, este estudo procurou comparar os resultados de TL e CDTE, além de absorção óptica, de vidros soda-lime com diferentes concentrações de Na POT.+ e K POT.+. Ao que tudo indica os processos responsáveis pela TL e CDTE dependem da relação entre as concentrações desses íons. Verificaram-se também variações com a taxa de dose, e os efeitos de tratamentos térmicos para situações onde um ou outro íon prevalece. / This work could be split in two different parts without impairment understanding. One of them, on natural topaz (Al2SiOdF,OH] 2) and the other on soda-lime silicate (SLS) glasses (Si02 + CaO + Na20) . In both of them we intend to contribute with more information on their defect composition, using some experimental techniques, especially the so called thermally stimulated depolarization currents (TSDC) . There are many surveys on topaz thermoluminescence (TL) and the possibility of its use as a TL dosimeter. So, one of the purposes of this study was to make a contribution with a technique not used so far with such material. We have detected three TSDC peaks. The results are not conclusive about the origin of those peaks, in part because we are dealing with a natural material whose composition can vary even within the same piece of crystal. As the SLS glasses, the study was more comprehensive. There are plenty of papers on irradiation effects in silicate glasses and attempts to understand the mechanisms responsible for them. It is believed that sodium plays a fundamental role in the main modifications caused by gamma irradiation of these glasses. In addition, this study attempts to compare the TL and TSDC results in SLS glasses with different concentrations of Na+ and K+. From our observations, the processes responsible for both TL and TSCD peaks depend on the relative concentrations of those ions. Furthermore, variations on the signals were also noticed; depending on the irradiation rate and on the thermal treatments performed, in samples where one or another ion prevails.

Trapping centres in as-grown TlInS2 layered single crystals have been studied by using a thermally stimulated current (TSC) technique. TSC measurements have been performed in the temperature range of 10-300 K with various heating rates. Experimental evidence has been found for the presence of five trapping centres with activation energies 12, 14, 400, 570 and 650 meV. Their capture cross-sections and concentrations were also determined. It is concluded that in these centres retrapping is negligible as confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. An exponential distribution of traps was revealed from the analysis of the TSC data obtained at different light excitation temperatures. The transmission and reflection spectra of TlInS2 crystals were measured over the spectral region of 400-1100 nm to determine the absorption coefficient and refractive index. The analysis of the room temperature absorption data revealed the coexistence of the indirect and direct transitions. The absorption edge was observed to shift toward the lower energy values as temperature increases from 10 to 300 K. The oscillator and the dispersion energies, and the zero-frequency refractive index were also reported. Furthermore, the chemical composition of TlInS2 crystals was determined from energy dispersive spectroscopic analysis. The parameters of monoclinic unit cell were found by studying the x-ray powder diffraction.

The discovery of the ferroelectric orthorhombic phase in doped hafnia films has sparked immense research efforts. Presently, a major obstacle for hafnia's use in high-endurance memory applications like nonvolatile random-access memories is its unstable ferroelectric response during field cycling. Different mechanisms are proposed to explain this instability including field-induced phase change, electron trapping, and oxygen vacancy diffusion. However, none of these is able to fully explain the complete behavior and interdependencies of these phenomena. Up to now, no complete root cause for fatigue, wake-up, and imprint effects is presented. In this study, the first evidence for the presence of singly and doubly positively charged oxygen vacancies in hafnia–zirconia films using thermally stimulated currents and impedance spectroscopy is presented. Moreover, it is shown that interaction of these defects with electrons at the interfaces to the electrodes may cause the observed instability of the ferroelectric performance.

Cette thèse s'inscrit dans la thématique technologique des décharges électrostatiques sur les panneaux solaires des satellites de télécommunication en orbite géostationnaire. Son objectif est de déterminer les évolutions des propriétés électriques d'un adhésif silicone commercial en environnement spatial et de les corréler aux évolutions de sa structure chimique. Les principaux constituants du matériau ont été identifiés et des échantillons dépourvus de particules de renfort - assimilés à la matrice polymère isolée - ont été élaborés. Afin d'évaluer l'influence des particules, ils ont été systématiquement comparés aux échantillons nominaux dans l'ensemble de ces travaux. La structure physico-chimique du matériau à l'état initial a été caractérisée en étudiant ses relaxations enthalpiques, mécaniques et en pratiquant des analyses chimiques. Son comportement électrique (relaxations dipolaires et conductivité) a été sondé grâce à une approche expérimentale inédite croisant la technique de relaxation de potentiel électrostatique de surface, la spectroscopie diélectrique dynamique et l'analyse des courants thermo-stimulés. Le vieillissement du matériau en environnement spatial a été simulé expérimentalement par l'exposition des échantillons à des flux élevés d'électrons de haute énergie. Les analyses chimiques, notamment en RMN du solide, ont montré la prédominance d'un processus de réticulation du matériau sous irradiation, et des mécanismes de dégradation à l'échelle microscopique ont été proposés. Le comportement électrique du matériau est fortement impacté par l'évolution de sa structure chimique : sa résistivité augmente considérablement avec la dose ionisante. Il est suggéré que la résistivité de ce matériau soit directement liée à son degré de réticulation, influant sur la mobilité des porteurs dans le cadre du hopping et de la percolation électrique. Cette augmentation est beaucoup plus marquée en présence de particules, ce qui a été attribué à la formation de nœuds de réticulation matrice-particules qui constituent des pièges plus profonds pour les porteurs de charges. Ces travaux apportent une meilleure compréhension des phénomènes de vieillissement des élastomères silicones en environnement spatial. Ils permettront d'anticiper des évolutions structurales qui pourraient mettre en péril leur fonction d'adhésion, ainsi que des évolutions de résistivité électrique intrinsèque, facteur décisif dans le déclenchement de décharges électrostatiques. / This PhD thesis falls within the technical field of electrostatic discharges occurring on the solar arrays of communications satellites in the geostationary orbit. Its main objective consists in assessing the evolutions of a space-used commercial silicone adhesive's electrical properties, and to correlate them with the evolutions of its chemical structure. The main components of this material have been identified, and neat samples (deprived of fillers) were elaborated so as to study the isolated polymer matrix. In order to assess the influence of filler incorporation, neat samples were systematically compared with the commercial ones in this study. The material's physicochemical structure in the initial state was characterized by studying its enthalpy relaxations, mechanical response, and by performing chemical analysis. Its electrical behavior (dipole relaxations and conductivity) was investigated thanks to an original experimental approach combining surface potential decay measurements, broadband dielectric spectroscopy, and thermally stimulated depolarization currents. Aging in the space environment was experimentally simulated by exposing the samples to high fluxes of high energy electrons. Chemical analysis (solid state NMR in particular) revealed the predominant crosslinking tendency of this material under ionizing radiations, and allowed to suggest degradation mechanisms at the microscopic scale. These structural evolutions also strongly impact its electrical behavior: a great increase in electrical resistivity has been observed with increasing ionizing dose. It is believed that electrical resistivity directly depends on the degree of crosslinking, which affects charge carrier mobility, in the theoretical frame of hopping and percolation models. The increase in resistivity is considerably more pronounced in the filled material, which could be associated with crosslinking occurring at the matrix-particles interface. Such crosslinks are thought to represent deeper traps for charge carriers. This work brought better understanding of aging phenomena in silicone elastomers exposed to the ionizing space environment. This knowledge will help predicting structural evolutions that may compromise vital properties such as adhesion, and the evolutions of intrinsic conductivity, a critical factor involved in the triggering of electrostatic discharges.

D’ençà que el polietilè reticulat (XLPE) es va començar a utilitzar com aïllament elèctric per cables de subministrament elèctric, s’han destinat molts esforços a l’estudi de les propietats dielèctriques del polietilè i l’efecte que la càrrega d’espai té sobre el seu comportament. En aquest sentit, les corrents de despolarització estimulades tèrmicament (TSDC) s’han utilitzat extensament per estudiar les relaxacions de càrrega d’espai. Aquesta tècnica ha demostrat tenir prou resolució per distingir diferències en aïllaments de XLPE amb composicions o processos de fabricació diferents. En aquesta tesi, els mecanismes de conducció dels aïllaments XLPE de cables de mitjana tensió (MV) han estat estudiats per TSDC i diverses tècniques complementàries, com l’anàlisi dinàmica elèctrica (DEA), les corrents d’absorció/resorció (ARC), el pols electroacústic (PEA) i les corrents de despolarització isotèrmiques (IDC). Altres tècniques, com l’espectroscòpia d’infrarojos (FTIR) o la difracció de raigs X, han estat també utilitzades per caracteritzar el material. S’han obtingut espectres TSDC per diferents mostres de cable, les quals en condicions de servei treballen en un rang de tensió AC de 12 a 20kV i a temperatures al voltant dels 90ºC. D’altra banda, s’han realitzat mesures de la conductivitat per ARC i DEA en mostres de cable, en cilindres de XLPE i en films. Les mesures s’han dut a terme a temperatures pertanyents al rang de fusió del XLPE (50–110ºC), en mostres sotmeses a aquestes temperatures durant diferents períodes de temps. Els resultats mostren diferències importants entre el comportament de les propietats conductives de les mostres de cable amb pantalles semiconductores (SC) i sense (cilindres de XLPE). El comportament observat ha estat explicat mitjançant la coexistència de dos mecanismes de conducció. La difusió d’impureses des de les pantalles SC determina el comportament d’una d’aquestes contribucions a mig i llarg termini. Els resultats obtinguts per FTIR són consistents amb aquest model. Respecte la microestructura, tant les mesures DSC com la difracció per raigs X mostren que existeixen processos de recristal•lització quan les mostres són sotmeses a temperatures ubicades dins del rang de fusió. Els electrets formats mitjançant el mètode de la polarització per finestres (WP) mostren una descàrrega TSDC amb un ample pic heteropolar en el rang de fusió, amb el màxim al voltant dels 105ºC. En treballs previs, aquest pic es va associar a la fusió de la fracció cristal•lina. Tanmateix, en lloc de decréixer quan la temperatura de polarització augmenta, el pic presenta una temperatura de polarització òptima al voltant de 90-95ºC. Aquest comportament ha estat explicat tenint en compte els processos de recristal•lització que es produeixen quan el material es polaritza isotèrmicament. Durant la recristal•lització, una nova fracció cristal•lina creix en un estat polaritzat degut el camp aplicat, i origina una corrent de despolarització quan es fon durant la mesura TSDC. Amb l’objectiu de determinar l’origen d’altres pics que apareixen en l’espectre TSDC del XLPE, s’han emprat les IDC com a tècnica complementària. Les corrents IDC obtingudes de mostres no tractades es poden representar com la combinació de dues contribucions diferenciades: un terme que és una funció potencial del temps i un d’exponencial. La segona relaxació es correspon amb un pic TSDC que apareix a 95ºC. D’aquesta manera s’ha pogut determinar l’origen dipolar del pic. Finalment, mitjançant la tècnica PEA s’ha obtingut la distribució de la càrrega d’espai en mostres polaritzades que havien estat sotmeses a diferents tractaments tèrmics. S’ha observat un comportament transitori tant per PEA com per TSDC. Tanmateix no s’ha pogut establir cap relació directa entre les descàrregues TSDC i mesures PEA. En conseqüència, s’ha proposat una explicació per les corbes TSDC que considera mecanismes que no són detectables en els perfils de càrrega obtinguts per PEA / Since cross-linked polyethylene (XLPE) started to be used as electrical insulation for power cables, much research has been focused on polyethylene dielectric properties and the effect of the space charge on its behavior. In this sense, thermally stimulated depolarization currents (TSDC) have been widely used to study space charge relaxation. This technique has proved to have enough resolution to determine differences in charge trapping properties among XLPE insulations with different composition and manufacturing processes. In this thesis work, the conduction mechanisms of medium voltage (MV) cable XLPE insulation have been studied by TSDC and several complementary techniques, such as dynamic electrical analysis (DEA), absorption/resorption currents (ARC), pulsed electroacoustic (PEA) and isothermal depolarization currents (IDC). Other techniques, like Fourier transform infrared (FTIR) spectroscopy or X-ray diffractometry, have been used to characterize the material. TSDC spectra have been obtained for different cable samples, which in service conditions work under AC voltages ranging from 12 to 20kV and at temperatures around 90ºC. On the other hand, conductivity measurements by ARC and DEA have been performed in cable samples and in XLPE cylinders, as well as XLPE films. Measurements have been carried out at temperatures within the melting temperature range of XLPE (50–110ºC) on samples annealed at such temperatures during several annealing times. Results show significant differences in the behavior of the conductive properties of XLPE cable samples with semiconducting (SC) screens and without them (XLPE cylinders). The observed behavior has been explained by the coexistence of two conduction mechanisms. Diffusion of impurities from SC screens determines the medium and long-term behavior of one of these contributions and, hence, of cable conductivity. FTIR results are consistent with this model. With respect to microstructure, DSC and X-ray diffractometry results show that recrystallization processes exist when samples are annealed in the melting range of temperatures. Electrets formed by means of the windowing polarization method (WP) showed a TSDC discharge with a wide heteropolar peak in the melting temperature range, and with the maximum at about 105ºC. This peak was associated with the melting of the crystalline fraction in previous works. However, in spite of decreasing with the temperature of polarization, an optimal polarization temperature around 90–95ºC is found. This behavior has been explained by taking into account recrystallization processes when the insulation is isothermally polarized. During recrystallization, the new crystalline fraction grows in a polarized state due to the applied electric field, and it causes the depolarization current when it melts during the TSDC measurement. Results obtained from different experiments are consistent with this assumption. With the aim to find out the origin of other TSDC peaks present in the spectrum of XLPE cable samples, IDC has been used as complementary technique. IDC currents obtained from as-received cable samples at temperatures close to service conditions can be considered as the combination of two different contributions: a power law current and a stretched exponential contribution. The last relaxation process has been successfully associated with with a TSDC peak found at 95ºC. By this way the dipolar origin of the peak has been determined. Finally, PEA measurements have provided the space charge distribution profiles of polarized samples with different annealings. A transient behavior has been observed in both PEA and TSDC measurements. However, no straightforward relation between TSDC discharges and space charge detected by PEA can be established. Therefore, an explanation for TSDC curves has been proposed, which considers mechanisms that are not noticeable in charge profiles obtained by PEA.

Electronic circuits comprising organic semiconductor thin-films are part of promising technologies for a renewable power generation and an energy-efficient information technology. Whereas TV and mobile phone applications of organic light emitting diodes (OLEDs) got ready for the market awhile ago, organic photovoltaics still lack in power conversion efficiencies, especially in relation to their current fabrication costs. A major reason for the low efficiencies are losses due to the large number of charge carrier traps in organic semiconductors as compared to silicon. It is the aim of this thesis to identify and quantify charge carrier traps in vacuum-deposited organic semiconductor thin-films and comprehend the reasons for the trap formation. For that, the techniques impedance spectroscopy (IS), thermally stimulated currents (TSC), and photoelectron spectroscopy are utilized. In order to assess the absolute energy of charge carrier traps, the charge carrier transport levels are computed for various hole transport materials such as MeO-TPD, pentacene, and ZnPc. Unlike inorganics, organic semiconductors possess in first-order approximation Gaussian distributed densities of states and temperaturedependent transport levels. The latter shift by up to 300 meV towards the energy gap-mid when changing from room temperature to 10 K as it is done for TSC examinations. The frequency-dependent capacitance response of charge carrier traps in organic Schottky diodes of pentacene and ZnPc are studied via impedance spectroscopy. In undoped systems, deep traps with depths of approx. 0.6 eV and densities in the order of 1016...1017 cm−3 are prevailing. For pentacene, the deep trap density is reduced when the material undergoes an additional purification step. Utilizing p-doping, the Fermi level is tuned in a way that deep traps are saturated. Vice versa, the freeze-out of p-doped ZnPc provides further insight into the influence of trap-filling, impurity saturation and reserve on the Fermi level position in organic semiconductors. Furthermore, charge carrier traps are investigated via thermally stimulated currents. It is shown that the trap depths are obtained correctly only if the dispersive transport of the released charge carriers until their extraction is considered. For the first time, the polarity of charge carrier traps in MeO-TPD, ZnPc, and m-MTDATA is identified from TSC’s differences in release time when spacer layers are introduced in the TSC samples. Simultaneously, tiny hole mobilities in the order of 10−13 cm2 Vs−1 are detected for low-temperature thin-films of the hole transporter material Spiro-TTB. It is shown for Spiro-TTB co-evaporated with the acceptor molecule F6-TCNNQ and a p-doped ZnPc:C60 absorber blend that the doping process creates shallow trap levels. Finally, various organic hole transport materials are examined upon their stability in water and oxygen atmosphere during sample fabrication and storage of the organic electronics. In case of pentacene, ZnPc, MeO-TPD, and m-MTDATA, hole traps are already present in unexposed thin-films, which increase in trap density upon oxygen exposure. A global trap level caused by oxygen impurities is found at energies of 4.7...4.8 eV that is detrimental to hole transport in organic semiconductors. / Elektronische Bauelemente aus Dünnschichten organischer Halbleiter sind Teil möglicher Schlüsseltechnologien zur regenerativen Energiegewinnung und energieeffizienten Informationstechnik. Während Fernseh- und Mobilfunkanwendungen organischer Leuchtdioden (OLEDs) bereits vor einiger Zeit Marktreife erlangt haben, ist die organische Photovoltaik (OPV) noch durch zu hohe Fertigungskosten in Relation zu unzureichenden Effizienzen unrentabel. Ein wesentlicher Grund für die niedrigen Wirkungsgrade sind Verluste durch die im Vergleich zu Silizium hohe Zahl an Ladungsträgerfallen in organischen Halbleitern. Ziel dieser Arbeit ist es, mittels Impedanz-Spektroskopie (IS), thermisch stimulierten Strömen (TSC) und Photoelektronenspektroskopie methodenübergreifend Ladungsträgerfallen in vakuumverdampften organischen Dünnschichten zu identifizieren, zu quantifizieren und ihre Ursachen zu ergründen. Um die Energie von Ladungsträgerfallen absolut beziffern zu können, wird zunächst für verschiedene Lochtransportmaterialien wie z.B. MeO-TPD, Pentazen und ZnPc die Transportenergie aus den in erster Ordnung gaußförmigen Zustandsdichten berechnet. Im Gegensatz zu anorganischen Halbleitern ist die Transportenergie in organischen Halbleitern temperaturabhängig. Sie verschiebt sich beim Übergang von Raumtemperatur zu 10 K, wie für TSC Untersuchungen bedeutsam, um bis zu 300 meV in Richtung der Bandlückenmitte. Mittels Impedanz-Spektroskopie wird die frequenzabhängige Kapazitätsantwort von Ladungsträgerfallen in organischen Schottky-Dioden aus Pentazen und ZnPc untersucht. In undotierten Systemen dominieren Defekte mit Tiefen um 0.6 eV, deren Dichte in der Größenordnung von 1016...1017 cm−3 liegt, sich aber im Fall von Pentazen durch einen zusätzlichen Materialaufreinigungsschritt halbieren lässt. Über p-Dotierung wird das Fermi-Level so eingestellt, dass tiefe Fallen abgesättigt werden können. Umgekehrt liefert das Ausfrieren von p-dotiertem ZnPc weitere Belege für den Einfluss von Fallenzuständen, Störstellen-Erschöpfung und Reserve auf das Fermi-Level in dotierten organischen Halbleitern. Im Weiteren werden Ladungsträgerfallen über thermisch stimulierte Ströme untersucht. Es wird gezeigt, dass die Fallentiefen nur dann konsistent bestimmt werden, wenn der dispersive Transport von freigesetzten Ladungsträgern zur Extraktionsstelle berücksichtigt wird. Durch Einführung von ’Abstandshalterschichten’ werden erstmalig über TSC die Polaritäten von Ladungsträgerfallen in MeO-TPD, ZnPc und m-MTDATA per Laufzeitunterschied bestimmt. Gleichzeitig werden geringste Löcherbeweglichkeiten in der Größenordnung von 10−13 cm2 Vs−1 für stark gekühlte Dünnschichten des Lochtransporters Spiro-TTB gemessen. Wie für Spiro-TTB koverdampft mit dem Akzeptormolekül F6-TCNNQ und p-dotierte Mischschichten der Absorbermaterialien ZnPc und C60 gezeigt, erzeugt Dotierung relativ flache Störstellen. Abschließend werden verschiedene organische Lochtransporter-Materialien auf ihre Stabilität in Wasser- und Sauerstoffatmosphären während der Prozessierung und der Lagerung fertiger elektronischer Bauelemente untersucht. Für Pentazen, ZnPc, MeO-TPD und m-MTDATA werden Löcherfallen in intrinsischen Dünnschichten nachgewiesen. Bei Kontakt mit Sauerstoff nimmt deren Defektdichte zu. Es findet sich ein universales Fallenniveau bei rund 4.7...4.8 eV, verursacht durch Sauerstoffverunreinigungen, welches den Lochtransport in organischen Halbleitern limitiert.

Electronic circuits comprising organic semiconductor thin-films are part of promising technologies for a renewable power generation and an energy-efficient information technology. Whereas TV and mobile phone applications of organic light emitting diodes (OLEDs) got ready for the market awhile ago, organic photovoltaics still lack in power conversion efficiencies, especially in relation to their current fabrication costs. A major reason for the low efficiencies are losses due to the large number of charge carrier traps in organic semiconductors as compared to silicon. It is the aim of this thesis to identify and quantify charge carrier traps in vacuum-deposited organic semiconductor thin-films and comprehend the reasons for the trap formation. For that, the techniques impedance spectroscopy (IS), thermally stimulated currents (TSC), and photoelectron spectroscopy are utilized. In order to assess the absolute energy of charge carrier traps, the charge carrier transport levels are computed for various hole transport materials such as MeO-TPD, pentacene, and ZnPc. Unlike inorganics, organic semiconductors possess in first-order approximation Gaussian distributed densities of states and temperaturedependent transport levels. The latter shift by up to 300 meV towards the energy gap-mid when changing from room temperature to 10 K as it is done for TSC examinations. The frequency-dependent capacitance response of charge carrier traps in organic Schottky diodes of pentacene and ZnPc are studied via impedance spectroscopy. In undoped systems, deep traps with depths of approx. 0.6 eV and densities in the order of 1016...1017 cm−3 are prevailing. For pentacene, the deep trap density is reduced when the material undergoes an additional purification step. Utilizing p-doping, the Fermi level is tuned in a way that deep traps are saturated. Vice versa, the freeze-out of p-doped ZnPc provides further insight into the influence of trap-filling, impurity saturation and reserve on the Fermi level position in organic semiconductors. Furthermore, charge carrier traps are investigated via thermally stimulated currents. It is shown that the trap depths are obtained correctly only if the dispersive transport of the released charge carriers until their extraction is considered. For the first time, the polarity of charge carrier traps in MeO-TPD, ZnPc, and m-MTDATA is identified from TSC’s differences in release time when spacer layers are introduced in the TSC samples. Simultaneously, tiny hole mobilities in the order of 10−13 cm2 Vs−1 are detected for low-temperature thin-films of the hole transporter material Spiro-TTB. It is shown for Spiro-TTB co-evaporated with the acceptor molecule F6-TCNNQ and a p-doped ZnPc:C60 absorber blend that the doping process creates shallow trap levels. Finally, various organic hole transport materials are examined upon their stability in water and oxygen atmosphere during sample fabrication and storage of the organic electronics. In case of pentacene, ZnPc, MeO-TPD, and m-MTDATA, hole traps are already present in unexposed thin-films, which increase in trap density upon oxygen exposure. A global trap level caused by oxygen impurities is found at energies of 4.7...4.8 eV that is detrimental to hole transport in organic semiconductors. / Elektronische Bauelemente aus Dünnschichten organischer Halbleiter sind Teil möglicher Schlüsseltechnologien zur regenerativen Energiegewinnung und energieeffizienten Informationstechnik. Während Fernseh- und Mobilfunkanwendungen organischer Leuchtdioden (OLEDs) bereits vor einiger Zeit Marktreife erlangt haben, ist die organische Photovoltaik (OPV) noch durch zu hohe Fertigungskosten in Relation zu unzureichenden Effizienzen unrentabel. Ein wesentlicher Grund für die niedrigen Wirkungsgrade sind Verluste durch die im Vergleich zu Silizium hohe Zahl an Ladungsträgerfallen in organischen Halbleitern. Ziel dieser Arbeit ist es, mittels Impedanz-Spektroskopie (IS), thermisch stimulierten Strömen (TSC) und Photoelektronenspektroskopie methodenübergreifend Ladungsträgerfallen in vakuumverdampften organischen Dünnschichten zu identifizieren, zu quantifizieren und ihre Ursachen zu ergründen. Um die Energie von Ladungsträgerfallen absolut beziffern zu können, wird zunächst für verschiedene Lochtransportmaterialien wie z.B. MeO-TPD, Pentazen und ZnPc die Transportenergie aus den in erster Ordnung gaußförmigen Zustandsdichten berechnet. Im Gegensatz zu anorganischen Halbleitern ist die Transportenergie in organischen Halbleitern temperaturabhängig. Sie verschiebt sich beim Übergang von Raumtemperatur zu 10 K, wie für TSC Untersuchungen bedeutsam, um bis zu 300 meV in Richtung der Bandlückenmitte. Mittels Impedanz-Spektroskopie wird die frequenzabhängige Kapazitätsantwort von Ladungsträgerfallen in organischen Schottky-Dioden aus Pentazen und ZnPc untersucht. In undotierten Systemen dominieren Defekte mit Tiefen um 0.6 eV, deren Dichte in der Größenordnung von 1016...1017 cm−3 liegt, sich aber im Fall von Pentazen durch einen zusätzlichen Materialaufreinigungsschritt halbieren lässt. Über p-Dotierung wird das Fermi-Level so eingestellt, dass tiefe Fallen abgesättigt werden können. Umgekehrt liefert das Ausfrieren von p-dotiertem ZnPc weitere Belege für den Einfluss von Fallenzuständen, Störstellen-Erschöpfung und Reserve auf das Fermi-Level in dotierten organischen Halbleitern. Im Weiteren werden Ladungsträgerfallen über thermisch stimulierte Ströme untersucht. Es wird gezeigt, dass die Fallentiefen nur dann konsistent bestimmt werden, wenn der dispersive Transport von freigesetzten Ladungsträgern zur Extraktionsstelle berücksichtigt wird. Durch Einführung von ’Abstandshalterschichten’ werden erstmalig über TSC die Polaritäten von Ladungsträgerfallen in MeO-TPD, ZnPc und m-MTDATA per Laufzeitunterschied bestimmt. Gleichzeitig werden geringste Löcherbeweglichkeiten in der Größenordnung von 10−13 cm2 Vs−1 für stark gekühlte Dünnschichten des Lochtransporters Spiro-TTB gemessen. Wie für Spiro-TTB koverdampft mit dem Akzeptormolekül F6-TCNNQ und p-dotierte Mischschichten der Absorbermaterialien ZnPc und C60 gezeigt, erzeugt Dotierung relativ flache Störstellen. Abschließend werden verschiedene organische Lochtransporter-Materialien auf ihre Stabilität in Wasser- und Sauerstoffatmosphären während der Prozessierung und der Lagerung fertiger elektronischer Bauelemente untersucht. Für Pentazen, ZnPc, MeO-TPD und m-MTDATA werden Löcherfallen in intrinsischen Dünnschichten nachgewiesen. Bei Kontakt mit Sauerstoff nimmt deren Defektdichte zu. Es findet sich ein universales Fallenniveau bei rund 4.7...4.8 eV, verursacht durch Sauerstoffverunreinigungen, welches den Lochtransport in organischen Halbleitern limitiert.