Tesi sul tema "Narrow band gap"

Historically, infrared (IR) detector technologies are connected mainly with controlling and night-vision problems: in a first stage, applications concerned simply with detection of IR radiation, but very soon capabilities to form IR images were developed, opening the way to systems for recognition and surveillance, especially for military purposes. Since the last decade of the twentieth century, the use of IR imaging systems for civil and peaceful purposes have increased continuously: these include medical and industrial applications, detection of earth resources, earth and universe sciences, etc. As an example, IR imaging is widely used in astronomy, to study interstellar medium and first-stages of stellar evolution; in medicine, IR thermography – IR imaging of the human body – is employed to detect cancers or other trauma; IR detectors are also widely used in automotive industry, chemical process monitoring, global monitoring of environmental pollution and climate changes, etc. The discovery in 1959 by Lawson and co-workers of the wide tunability of the HgCdTe alloy allowed this compound to become one of the most important and versatile materials for detector applications over the entire IR range. A critical contribution to research is given by Technology Computer-Aided Design (TCAD), modeling and simulation. In the first part of this thesis, I present the main part of my research activity, focused on the development of abilities and methodologies for the simulation of realistic three-dimensional HgCdTe-based infrared photodetectors. The purpose is the investigation of generation-recombination (GR) mechanisms and modeling of spectral photoresponse in narrow-gap HgCdTe-based photodetectors, with one-, two and three-dimensional (1D, 2D, 3D) realistic TCAD models (Chapters 1-5). Another important topic of industrial research in semiconductor physics deals with nitride-based light-emitting diodes (LEDs). From automotive to streetlights, from lights in our houses to the displays of TVs and smartphones, LED-based technology is making its way in the market. This proliferation would have been impossible without GaN-based LEDs, whose invention by Isamu Akasaki, Hiroshi Amano and Shuji Nakamura has been rewarded with the 2014 Nobel Prize in Physics. Nevertheless, GaN-based LEDs performanceis limited by a reduction (droop) of their internal quantum efficiency (IQE) as the driving current density is increased beyond 10 A/cm2, whose physical origin is still under intense debate. In the second part of this thesis, I present a quantum model, based on condensed matter many-body theory, that allowed to obtain the electron capture time and hot-electron intraband relaxation times in a quantum well (QW)-barrier heterostructure, for longitudinal optic (LO) phonon emission, as function of carrier density. The interaction was described in the Single Plasmon Pole of the Random Phase Approximation, retaining the full density-, energy- and wavevector-dependent form of the dielectric function (Chapters 6-7).

Generation of terahertz radiation from semiconductor surfaces has great potential for investigation of physical properties of semiconductors. This work focuses on the semiconductor research when generating terahertz pulses from a variety of semiconductor surfaces. THz radiation from semiconductor surfaces can be generated on a whole range of physical mechanisms: the surface field screening, photo-Dember effect, the optical rectification, electric field induced optical rectification, plasma oscillations, coherent phonons and plasmons. A number of important semiconductor parameters such as refractive index, mobility, carrier relaxation time and higher conductivity valley positions can be measured using THz generation from semiconductor surface technique. In this work THz radiation generation mechanisms were investigated when changing excitation conditions: ambient temperature, magnetic field, laser wavelength and intensity, pulse duration. After tests with variety different semiconductors it was found that p-InAs is the best surface emitter when excitation laser wavelength is 800 nm. Using THz excitation spectroscopy the intervalley distances were measured directly, for the first time, in two InxGa1-xAs, InAs and InSb samples.
THz spinduliuotės generavimas iš puslaidininkių paviršiaus turi didelį potencialą puslaidininkių fizikinėms savybėms tirti. Šis darbas skiriamas puslaidininkių tyrimams generuojant THz impulsus iš jų paviršių, apšviestų femtosekundiniais lazerio impulsais. THz spinduliuotė iš puslaidininkių paviršių gali būti generuojama dėl visos eilės fizikinių mechanizmų: paviršinio lauko ekranavimo, foto-Demberio efekto, optinio lyginimo, elektriniu lauku indukuoto optinio lyginimo, plazminių svyravimų, koherentinių fononų ir plazmonų. Tiriant THz spinduliuotės generacijos mechanizmus galima išmatuoti daug svarbių puslaidininkių parametrų, tokių kaip lūžio rodiklis, judris, krūvininkų gyvavimo trukmė, aukštesniųjų laidumo slėnių padėtys. Darbo metu tirti THz spinduliuotės generacijos puslaidininkio paviršiuje mechanizmai keičiant žadinimo sąlygas: aplinkos temperatūrą, magnetinį lauką, žadinančio lazerio bangos ilgį ir intensyvumą, bei impulso trukmę. Ištyrus visą eilę įvairių puslaidininkių nustatyta, kad geriausias THz spinduliuotės emiteris žadinant 800 nm bangos ilgio spinduliuote yra p-InAs. Pirmą kartą THz žadinimo spektroskopijos metodu tiesiogiai išmatuoti tarpslėniniai atstumai InxGa1-xAs , InAs ir InSb bandiniuose.

Various techniques to synthesize nanowires and nanotubes as a function of growth temperature and time were investigated. These include growth of nanowires by a chemical vapor deposition (CVD) system using vapor-liquid-solid (VLS) growth mechanism and electro-chemical synthesis of nanowires and nanotubes. Narrow band gap InSb Eg = 0.17 eV at room temp) nanowires were successively synthesized. Using a phase diagram, the transition of the nanowire from metallic- semiconducting- semi-metallic phase was investigated. A thermodynamic model is developed to show that the occurrence of native defects in InSb nanowires influenced by the nanowire growth kinetics and thermodynamics of defect formation. Wide band gap ZnO (Eg = 3.34 eV) and In2O3 (3.7 eV) were also synthesized. ZnO nanowires and nanotubes were successfully doped with a transition metal Fe, making it a Dilute Magnetic Semiconductor of great technological relevance. Structural and electronic characterizations of nanowires were studied for different semiconducting, metallic and semi-metallic nanowires. Electron transport measurements were used to estimate intrinsic material parameters like carrier concentration and mobility. An efficient gas sensing device using a single In2O3 nanowire was studied and which showed sensitivity to reducing gas like NH3 and oxidizing gas like O2 gas at room temperature. The efficiency of the gas sensing device was found to be sensitive to the nature of contacts as well as the presence of surface states on the nanowire.

The work described in this thesis investigates the effects of bandstructure modifications, brought about by Landau confinement, hydrostatic pressure and uniaxial stress, on recombination processes in narrow-gap materials and laser diodes. The effects of Landau confinement on the characteristics of InSb-based emission devices operating at a wavelength of ~5mum at 77K were studied. The change in performance due to the magnetic field applied along both the cavity and the growth direction and thereby simulating quasi-quantum wire and quasi-quantum dot structures clearly demonstrated the benefits, such as reduced threshold and temperature sensitivity, gained by the reduced dimensionality. On the other hand, suppression of LO-phonon emission due to the discrete nature of the density of states was observed, for the first time, in an interband laser device. Interband recombination dynamics were studied in In1-xGaxSb and PbSe over a range of excited carrier densities and temperatures down to 30K. Detailed analysis of the results found that the Auger-1 mechanism is reduced in In1-xGaxSb as a function of Ga-fraction due to the increased bandgap energy, in good agreement with theoretical predictions. In PbSe, the Auger-1 rate was observed to dominate at low excited carrier concentrations in spite of near-mirror bands, and was found to be approximately constant between 300K and 70K and was seen to be quenched in the low temperature regime. Stimulated emission was seen to be the most efficient recombination mechanism at high excited carrier densities at low temperatures. The Auger coefficient in PbSe was found to be one to two orders of magnitude lower than for materials with a Kane band structure (Hg1-xCdxTe) with comparable bandgap. An experimental technique was developed which enables measurements at high hydrostatic pressures and high magnetic fields at low temperatures. Hydrostatic pressures were applied to a 1.5mum laser diode at different temperatures revealing the effects of pressure on the band structure and hence the laser characteristics. A visible laser diode was measured under the simultaneous application of hydrostatic pressure and uniaxial stress. The change in performance was satisfactorily explained in terms of leakage of carriers into the X-minimum in the cladding region, the process that has been suspected of being one of the major loss mechanisms in visible laser diodes. This copy of the thesis has been supplied on the condition that anyone who consults it is understood to recognise that the copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the prior written consent of the author or the University (as may be appropriate).

This thesis is focused on the growth of narrow band gap semiconductor nanowires (NWs) on silicon and graphite by droplet epitaxy. First, the growth conditions of In droplets suitable for the nucleation of NWs was identified. Vertically-aligned and non-tapered InAs NWs were then realized on bare Si. It is shown that the diameter and areal density of NWs are defined by the geometry of pre-deposited In droplets. The NWs exhibit a dominant PL peak associated with the band to band (BtB) emission in addition to a distinct BtB temperature dependent red-shift, strong emission efficiency (up to 2500C) and record narrow spectral linewidth of ~20 meV (at 10K) which is relatively smaller than previously reported values. This demonstrates the high optical properties of the droplet epitaxy grown InAs NWs. Vertically-aligned and non-tapered InAs1-xSbx NWs have been demonstrated on Si without the commonly used NWs stems. In addition, the effect of Sb addition to the morphology of self-catalyzed InAsSb NWs grown directly on Si is systematically investigated for the first time. It is shown that trace Sb flux significantly promotes lateral NWs growth while at the same time suppressing axial growth. Furthermore, Sb-induced crystal phase evolution is elucidated as a function of Sb content. Although, pure InAs NWs show a mixture of Wurtzite (WZ) and Zinc-Blende (ZB) phases, a crystal phase evolution from a highly polytypic InAs to a quasi-pure WZ InAsSb NWs (2-4% Sb content) and a quasi-pure ZB InAsSb NWs crystals (~10% Sb content) is demonstrated in addition to a significant reduction in the stacking fault density in as-grown NWs with increasing Sb content. The recent discovery of flexible graphene has triggered a new wave of optoelectronic revolution. In order to fully exploit the enormous potential of functional monolithic NWs/graphene hybrid structures, the optimal growth conditions for realizing morphologically and structurally superior InAs NWs on graphitic substrates has been identified. Vertically well-aligned and thin InAs NWs were obtained in a narrow growth window of 420-450oC while a high yield of NWs was realized within a restricted domain of growth rate and V/III flux ratio. Compared to the growths on Si, the graphitic substrate is shown to enhance adatom mobility and enable growth at high growth rate which is highly promising for cost-effective devices. In addition, the NWs on graphite show a significantly reduced density of defect in comparison to the growth on conventional Si substrates owing to van der Waals epitaxy growth technique resulting from the absence of dangling bonds. Moreover, high aspect ratio NWs are essential for functional device applications however, the growth of thin InAs1-xSbx NWs is extremely challenging owing to Sb-induced lateral growth. The growth of ultra-high aspect ratio InAs1-xSbx NWs (0 ≤ x ≤ 0.12) on graphite is demonstrated for the first time at highly As-rich conditions with potential for applications in ultra-sensitive, eco-friendly, flexible and cost-effective infrared photodetectors. It is shown that the graphitic thin film promotes Sb incorporation and is more favourable for InAsSb NWs growth in comparison to Si substrates. Finally, a morphological evolution from InN NCs to three dimensional (3D) InN islands is demonstrated with increasing growth temperature attributable to lowered surface free energy of the growing crystals with disproportionate growth velocities along different growth fronts.

Ce manuscrit se consacre au développement d'oligomères à base de platine en tant que nouveaux donneurs pour des cellules solaires organiques à hétérojonction en vrac, dans le but d'améliorer leurs performances par le biais de modifications structurelles. Le travail est divisé en trois parties principales. La première partie examine comment réduire la bande interdite des [Pt]-oligomères en modifiant la structure du ligand. Cette adaptation vise à accroître la longueur de conjugaison, la planéité, la stabilisation des quinones et à renforcer l'effet "push-pull", notamment grâce à l'ajout de 3,4éthylènedioxythiophène (EDOT). Cette approche a conduit à la création de nouveaux matériaux donneurs qui ont atteint une efficacité de conversion de puissance (ECP) moyenne de 14,81% avec des accepteurs non-fullérènes dans des cellules solaires à hétérojonction en vrac binaires, et de 15.97% dans des cellules ternaires à hétérojonction en vrac. La deuxième partie se concentre sur l'amélioration de l'organisation moléculaire des [Pt]-oligomères en intégrant un groupe mésogène discotique de triphénylène dans la structure conjuguée au moyen d'un espaceur. Il a été démontré que remplacer un espaceur triazole rigide par un espaceur aliphatique linéaire plus flexible améliorait les propriétés des [Pt]-oligomères, entraînant une augmentation de l'efficacité de conversion photovoltaïque, passant de 13 % à 15 %. Enfin, la troisième partie explore des pistes d'amélioration supplémentaires en synthétisant des [Pt]-oligomères dotés de longueurs de conjugaison étendues, associés à un groupe organisateur discotique relié par un espaceur aliphatique. Les ligands qui combinent l'EDOT et le groupe triphénylène, reliés par un espaceur aliphatique, ont affiché des propriétés prometteuses, soulignant ainsi l'importance de poursuivre ces travaux de synthèse pour tester et valider pleinement ces [Pt]-oligomères améliorés
This manuscript focuses on developing [Pt]-oligomers as novel donors for bulk heterojunction organic solar cells, aiming to enhance their performance through structural modifications. The work is divided into three main parts. The first part addresses the reduction of the band gap in [Pt]-oligomers by modifying the ligand structure to improve conjugation length, planarity, quinone stabilization, and the "push-pull" effect, specifically through the inclusion of 3,4ethylenedioxythiophene (EDOT). This approach led to new donor materials that achieved an average power conversion efficiency (PCE) of 14.81% with non-fullerene acceptors in binary bulk heterojunction solar cells and 15.97% in ternary bulk heterojunction cells. The second part focuses on enhancing the molecular organization of [Pt]-oligomers by integrating a triphenylene discotic mesogenic group into the conjugated backbone via a spacer. It was found that replacing a rigid triazole spacer with a more flexible linear aliphatic spacer improved the properties of the [Pt]-oligomers, resulting in an increase in the average PCE from 13.36% to 15.93%. The third part explores further improvements by synthesizing [Pt]oligomers with extended conjugated lengths and a discotic organizing group connected through an aliphatic spacer. Ligands that incorporate both EDOT and the triphenylene group, connected by an aliphatic spacer, demonstrated promising properties, suggesting the need for further synthesis to fully test and validate these improvements on [Pt]-oligomers

This thesis tackles issues of particular interest regarding analysis and design of passive components at the mm-wave and Terahertz (THz) bands. Innovative analysis techniques and modeling of complex structures, design procedures, and practical implementation of advanced passive devices are presented. The first part of the thesis is dedicated to THz passive components. These days, THz technology suffers from the lack of suitable waveguiding structures since both, metals and dielectric, are lossy at THz frequencies. This implies that neither conventional closed metallic structures used at microwave frequencies, nor dielectric waveguides used in the optical regime, are adequate solutions. Among a variety of new proposals, the Single Wire Waveguide (SWW) stands out due to its low attenuation and dispersion. However, this surface waveguide presents difficult excitation and strong radiation on bends. A Dielectric-Coated Single Wire Waveguide (DCSWW) can be used to alleviate these problems, but advantages of the SWW are lost and new problems arise. Until now, literature has not given proper solution to radiation on bends and, on the other hand, rigorous characterization of these waveguides lacks these days. This thesis provides, for the first time, a complete modal analysis of both waveguides, appropriated for THz frequencies. This analysis is later applied to solve the problem of radiation on bends. Several structures and design procedures to alleviate radiation losses are presented and experimentally validated. The second part of the thesis is dedicated to mm-wave passive components. These days, when implementing passive components to operate at such small, millimetric wavelengths, to ensure proper metallic contact and alignment between parts results challenging. In addition, dielectric absorption becomes significant at mm-wave frequencies. Consequently, conventional hollow metallic waveguides and planar transmission lines present high attenuation so that new topologies are being considered. Gap Waveguides (GWs), based on a periodic structure introducing an Electromagnetic Bandgap effect, result very suitable since they do not require metallic contacts and avoid dielectric losses. However, although GWs have great potential, several issues prevent GW technology from becoming consolidated and universally used. On the one hand, the topological complexity of GWs difficulties the design process since full-wave simulations are time-costly and there is a lack of appropriate analysis methods and suitable synthesis procedures. On the other hand, benefits of using GWs instead of conventional structures are required to be more clearly evidenced with high-performance GW components and proper comparatives with conventional structures. This thesis introduces several efficient analysis methods, models, and synthesis techniques that will allow engineers without significant background in GWs to straightforwardly implement GW devices. In addition, several high-performance narrow-band filters operating at Ka-band and V-band, as well as a rigorous comparative with rectangular waveguide topology, are presented.
Esta tesis aborda problemas actuales en el análisis y diseño de componentes pasivos en las bandas de onda milimétrica y Terahercios (THz). Se presentan nuevas técnicas de análisis y modelado de estructuras complejas, procedimientos de diseño, e implementación práctica de dispositivos pasivos avanzados. La primera parte de la tesis se dedica a componentes pasivos de THz. Actualmente no se disponen de guías de onda adecuadas a THz debido a que ambos, metales y dieléctricos, introducen grandes pérdidas. En consecuencia, no es adecuado escalar las estructuras metálicas cerradas usadas en microondas, ni las guías dieléctricas usadas a frecuencias ópticas. Entre un gran número de recientes propuestas, la Single Wire Waveguide (SWW) destaca por su baja atenuación y casi nula dispersión. No obstante, como guía superficial, la SWW presenta difícil excitación y radiación en curvas. El uso de un recubrimiento dieléctrico, creando la Dielecric-Coated Single Wire Waveguide (DCSWW), alivia estos inconvenientes, pero las ventajas anteriores se pierden y nuevos problemas aparecen. Hasta la fecha, no se han encontrado soluciones adecuadas para la radiación en curvas de la SWW. Además, se echa en falta una caracterización rigurosa de ambas guías. Esta tesis presenta, por primera vez, un análisis modal completo de SWW y DCSWW, adecuado a la banda de THz. Este análisis es aplicado posteriormente para evitar el problema de la radiación en curvas. Se presentan y validan experimentalmente diversas estructuras y procedimientos de diseño. La segunda parte de la tesis abarca componentes pasivos de ondas milimétricas. Actualmente, estos componentes sufren una importante degradación de su respuesta debido a que resulta difícil asegurar contacto metálico y alineamiento adecuados para la operación a longitudes de onda tan pequeñas. Además, la absorción dieléctrica incrementa notablemente a estas frecuencias. En consecuencia, tanto guías metálicas huecas como líneas de transmisión planares convencionales presentan gran atenuación, siendo necesario considerar topologías alternativas. Las Gap Waveguides (GWs), basadas en una estructura periódica que introduce un efecto de Electromagnetic Bandgap, resultan muy adecuadas puesto que no requieren contacto entre partes metálicas y evitan las pérdidas en dieléctricos. No obstante, a pesar del potencial de las GWs, varias barreras impiden la consolidación y uso universal de esta tecnología. Por una parte, la compleja topología de las GWs dificulta el proceso de diseño dado que las simulaciones de onda completa consumen mucho tiempo y no existen actualmente métodos de análisis y diseño apropiados. Por otra parte, es necesario evidenciar el beneficio de usar GWs mediante dispositivos GW de altas prestaciones y comparativas adecuadas con estructuras convencionales. Esta tesis presenta diversos métodos de análisis eficientes, modelos, y técnicas de diseño que permitirán la síntesis de dispositivos GW sin necesidad de un conocimiento profundo de esta tecnología. Asimismo, se presentan varios filtros de banda estrecha operando en las bandas Ka y V con altas prestaciones, así como una comparativa rigurosa con la guía rectangular.
Aquesta tesi aborda problemes actuals en relació a l'anàlisi i disseny de components passius en les bandes d'ona mil·limètrica i Terahercis. Es presenten noves tècniques d'anàlisi i modelatge d'estructures complexes, procediments de disseny, i implementació pràctica de dispositius passius avançats. La primera part de la tesi es focalitza en components passius de THz. Actualment no es disposen de guies d'ona adequades a THz causa que tots dos, metalls i dielèctrics, introdueixen grans pèrdues. En conseqüència, no és adequat escalar les estructures metál·liques tancades usades en microones, ni les guies dielèctriques usades a freqüències òptiques. Entre un gran nombre de propostes recents, la Single Wire Waveguide (SWW) destaca per la seua baixa atenuació i quasi nul·la dispersió. No obstant això, com a guia superficial, la SWW presenta difícil excitació i radiació en corbes. L'ús d'un recobriment dielèctric, creant la Dielecric-Coated Single Wire Waveguide (DCSWW), alleuja aquests inconvenients, però els avantatges anteriors es perden i nous problemes apareixen. Fins a la data, no s'han trobat solucions adequades per a la radiació en corbes de la SWW. A més, es troba a faltar una caracterització rigorosa d'ambdues guies. Aquesta tesi presenta, per primera vegada, un anàlisi modal complet de SWW i DCSWW, adequat a la banda de THz. Aquest anàlisi és aplicat posteriorment per evitar el problema de la radiació en corbes. Es presenten i validen experimentalment diverses estructures i procediments de disseny. La segona part de la tesi es centra en components passius d'ones mil·limètriques. Actualment, aquests components pateixen una important degradació de la seua resposta a causa de que resulta difícil assegurar contacte metàl·lic i alineament adequats per a l'operació a longituds d'ona tan menudes. A més, l'absorció dielèctrica incrementa notablement a aquestes freqüències. En conseqüència, tant guies metàl·liques buides com línies de transmissió planars convencionals presenten gran atenuació, sent necessari considerar topologies alternatives. Les Gap Waveguides (GWs), basades en una estructura periòdica que introdueix un efecte de Electromagnetic Bandgap, resulten molt adequades ja que no requereixen contacte entre parts metàl·liques i eviten les pèrdues en dielèctrics. No obstant, tot i el potencial de les GWs, diverses barreres impedixen la consolidació i ús universal d'aquesta tecnologia. D'una banda, la complexa topologia de les GWs dificulta el procés de disseny atés que les simulacions d'ona completa consumeixen molt de temps i no existeixen actualment mètodes d'anàlisi i disseny apropiats. D'altra banda, és necessari evidenciar el benefici d'utilitzar GWs mitjançant dispositius GW d'altes prestacions i comparatives adequades amb estructures convencionals. Aquesta tesi presenta diversos mètodes d'anàlisi eficients, models, i tècniques de disseny que permetran la síntesi de dispositius GW sense necessitat d'un coneixement profund d'aquesta tecnologia. Així mateix, es presenten diversos filtres de banda estreta operant en les bandes Ka i V amb altes prestacions, així com una comparativa rigorosa amb la guia rectangular.
Berenguer Verdú, AJ. (2017). Analysis and design of efficient passive components for the millimeter-wave and THz bands [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/84004
TESIS

Le tellurure de mercure et de cadmium (HgCdTe ou MCT) est un matériau reconnu pour la physique de la matière condensée, dont l'histoire, datant aujourd'hui de plus de cinquante ans, constitue un excellent exemple des progrès remarquables réalisés dans la recherche sur les semi-conducteurs et les semi-métaux. Notre travail est principalement motivé par l’intérêt fondamental que suscitent ces systèmes, mais notre recherche peut également avoir un impact pratique (indirect) sur la médecine, la surveillance ou la détection de l’environnement ainsi que sur les systèmes de sécurité. Cela peut aider à améliorer les performances des photodétecteurs dans la limite des grandes longueurs d'onde ou à faciliter la fabrication de dispositifs émettant de la lumière.La présente thèse de doctorat vise principalement à combler certaines des lacunes de notre compréhension de la structure de bande électronique des hétérostructures 2D et quasi-2D basées sur les matériaux HgTe/HgCdTe et InAs/InSb, qui peuvent être transformés en phase topologiquement isolante à l'aide des paramètres de croissance. Pour explorer leurs propriétés, la technique expérimentale de base, la magnéto-spectroscopie infrarouge et THz fonctionnant dans un large éventail de champs magnétiques, est combinée à des mesures complémentaires de magnéto-transport. Cette combinaison de méthodes expérimentales nous permet d’obtenir de précieuses informations sur les états électroniques non seulement à l’énergie de Fermi, mais également dans son voisinage relativement large. Diverses hétérostructures ont été étudiées avec des caractéristiques globales et/ou spécifiques déterminées principalement par les paramètres de croissance.La réponse magnéto-optique observée, due aux excitations intra-bande (résonance cyclotron) et interbandes (entre les niveaux de Landau) peut être interprétée dans le contexte d'études antérieures sur des échantillons 3D, des puits quantiques et des super-réseaux, mais également en rapport aux attentes théoriques. Ici, nous visons à obtenir une explication quantitative des données expérimentales recueillies, mais également à développer un modèle théorique fiable. Ce dernier comprend le réglage précis des paramètres de structure de bande présents dans le modèle établi de Kane, mais surtout, l'identification de termes supplémentaires pertinents (d'ordre élevé) nécessaires pour parvenir à un accord quantitatif avec nos expériences. On peut s’attendre à ce que les corrections dues à ces termes supplémentaires affectent davantage les sous-bandes de valence, généralement caractérisées par des masses effectives relativement importantes et, par conséquent, par une grande densité d’états ou, lorsque le champ magnétique est appliqué, par un espacement assez étroit (et mélange important) des niveaux de Landau
Mercury cadmium telluride (HgCdTe or MCT) is a time-honored material for condensed matter physics, whose history  nowadays more than fifty years long  may serve as an excellent example of remarkable progress made in research on semiconductors and semimetals. The ternary compound HgCdTe implies two important aspects, which largely contributed to its undoubted success in solid-states physics.The present PhD thesis primarily aims at filling some of existing gaps in our understanding of the electronic band structure in 2D and quasi-2D heterostructures based on HgTe/HgCdTe and InAs/InSb materials, which both may be tuned into topologically insulating phase using particular structural parameter. To explore their properties, the primal experimental technique, infrared and THz magneto-spectroscopy operating in a broad of magnetic fields, is combined with complementary magneto-transport measurements. This combination of experimental methods allows us to get valuable insights into electronic states not only at the Fermi energy, but also in relatively broad vicinity.The observed magneto-optical response - due to intraband (cyclotron resonance) and interband inter-Landau level excitations - may be interpreted in the context of previous studies performed on bulk samples , quantum wells and superlattices, but also compared with theoretical expectations. Here we aim at achieving the quantitative explanation of the collected experimental data, but also further developing a reliable theoretical model. The latter includes the fine-tuning of the band structure parameters present in the established Kane model, but even more importantly, identifying additional relevant (high-order) terms and finding their particular strengths, needed to achieve quantitative agreement with our experiments. One may expect that corrections due to these additional terms will more affect the valence subbands, which are in general characterized by relatively large effective masses. Consequently, valence subbands have larger density of states compared to conduction band or, when the magnetic field is applied, rather narrow spacing (and possibly large mixing) of Landau levels

碩士
明道大學
材料科學與工程學系碩士班
97
Abstract In this research, the hydrogenated amorphous silicon films (a-Si:H) and hydrogenated silicon germanium (a-SiGe:H) films were deposited using by High-frequency plasma enhanced chemical vapor deposition (HF-PECVD). For intrinsic Si layer research, pressure effect on the properties of Si films were investigated. The properties of intrinsic Si films such as deposition rate, crystalline fraction, absorption coefficient, band gap, dark conductivity, photo conductivity, hydrogen content and microstructure factor as function as deposition pressure. We investigated the pressure effects of growth mechanisms and properties on silicon films. High-quality both intrinsic and doped a-Si layers have been deposited in this paper. We report a narrow bandgap a-SiGe:H films with high photosensitivity using the mixture of SiH4 and GeH4 with H2 dilution. The effects of GeH4 / (SiH4 + GeH4 + H2) ratio on the properties of a-SiGe:H films are characterized by Raman spectrometer, X-ray photoelectron spectrometer, X-ray diffractometer spectrometer, Fourier transform infrared absorption spectroscopy, UV–Visible spectroscopy and scanning electron microscopy. We found that band gap decreases with increasing Ge content. We report the influence of Ge content on the properties of a-SiGe:H films and performance of p-i-n solar cells. The a-SiGe thin film solar cells with a Voc of 0.74 V, a Jsc of 9.9 mA/cm2 ,a fill factor of 0.60 and a maximum efficiency of 4.42 % were obtained.

博士
國立交通大學
材料科學與工程系所
97
First, novel twelve narrow-band-gap conjugated copolymers consisting of the comonomers alkyl-substituted fluorene and mono- and bis-(2-aryl-2-cyanovinyl)-10-hexylphenothiazine were copolymerized by a padallium-catalyzed Suzuki coupling reaction with two different feed ratios. The polymers showed broad optical absorption from 400 to 800 nm with optical band gaps at 1.55-2.10 eV. Second, other novel groups of five cyclopentadithiophene-based copolymers employing arylcyanovinyl and keto groups in different molar ratios were also synthesized successfully by palladium (0)-catalyzed Suzuki coupling reactions. Finally, six novel conjugated copolymers containing coplanar cyclopentadithiophene units (incorporated with bithiazole/thienyl-based monomers) were synthesized and developed for the applications of polymer solar cells (PSCs). For these cyclopentadithiophene-based copolymers, they showed broad optical absorption from 400 to 900 nm with optical band gaps at 1.38-1.94 eV. Powder X-ray diffraction (XRD) analyses suggested that these copolymers formed highly self-assembled π-π stackings. Under 100 mW/cm2 of AM 1.5 white-light illumination, as blended with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as an electron acceptor in bulk heterojunction photovoltaic devices, narrow-band-gap polymers as electron donors showed significant photovoltaic performance which varied with the intramolecular donor-acceptor interaction and their mixing ratios to PCBM. The PSC device in the weight ratio of 1:2 with PCBM gave the best preliminary result with an overall power conversion efficiency (PCE) of 3.04%, an open-circuit voltage of 0.70 V, a short-circuit current of 8.00 mA/cm2, and a fill factor of 53.7%.

博士
國立交通大學
材料科學與工程學系
99
The prime aim of this review is to bring together the areas of narrow band-gap conjugated polymers, dyes, and the supramolecular self assemblies of both dyes and polymers for the applications of organic solar cells. In the first chapter, a brief introduction of evolution of different types of solar cells has been given and also surveyed the literatures for the different structures of conjugated systems which can be efficient for the applications of organic solar cells. In the Second chapter two series of novel symmetrical acceptor-donor-acceptor organic sensitizers (M1-M3 and M4-M6) containing 3,6- and 2,7-functionalized carbazole (donor) cores, respectively, connected with two anchoring cyanoacrylic acid (acceptor) termini via different numbers (2 or 3) of conjugated thienyl linkers (w or w/o hexyl side-chains), were designed and synthesized. The effects of the molecular planarity originated from the central electron-donating 3,6- and 2,7-functionalized carbazole cores on device performance were studied. A structure-based density functional theory (DFT) calculation confirmed the efficiencies of the dyes being related to the coplanarity of the carbazole cores with respect to the linked thiophene units. Molecular orbital analyses reflected the characterstics of the carbazole-based highest occupied molecular orbitals (HOMOs) and acid-based lowest unoccupied molecular orbitals (LUMOs) along with the bridged thiophene units were essential for strong conjugations across the donor-acceptor groups, while time-dependent density functional theory (TDDFT) calculations allowed the assignment of HOMO–LUMO transitions (>90%) of the low energy bands in these new systems. Among these dyes, the best dye sensitized solar cell (DSSC) performance was obtained from the DSSC device containing M1, bearing 3,6-functionalized carbazole center linked by two symmetrical bithiophene groups, with an overall power conversion efficiency (讯) value of 4.82%, an open circuit voltage (Voc) of 0.61 V, a short circuit photocurrent density (Jsc) of 12.66 mA/cm2, and a fill factor (FF) of 0.62 under standard AM 1.5 sunlight with a maximum incident photon to current conversion efficiency (IPCE) of 68%. Furthermore, it is very impressive to observe the IPCE and Jsc values of the DSSCs in TiO2-based thin films (3 μm) containing M1 and M5 dyes were higher than those of the DSSC containing ruthenium-based N719 sensitizer. In the third chapter four novel symmetrical organic dyes (S1-S4) configured with acceptor-donor-acceptor (A-D-A) structures containing electron donating fluorene (S1 and S2) and N-alkyl dithieno[3,2-b:2',3'-d]pyrrole (DTP) (S3 and S4) cores terminated with two anchoring cyanoacrylic acids (as electron-acceptors) were synthesized and applied to dye-sensitized solar cells (DSSCs). The DSSC device based on S2 dye showed the best photovoltaic performance among S1-S4 dyes: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 76%, a short circuit current (Jsc) of 12.27 mA/cm2, an open circuit voltage (Voc) of 0.61 V, a fill factor (FF) of 0.63, and an overall power conversion efficiency (η) of 4.73%. Besides, the utilization of chenodoxycholic acid (CDCA) as a co-adsorbent in the DSSC device based on S3 dye showed a significant improvement in its η value (from 3.70% to 4.31%), which is attributed to the suppression of dye aggregation on TiO2 surface and thus to increase the Jsc value eventually. In the fourth chapter a series of novel low-bandgap triphenylamine-based conjugated polymers (PCAZCN, PPTZCN, and PDTPCN) consisting of different electron-rich donor main chains (N-alkyl-2,7-carbazole, phenothiazine, and cyclopentadithinopyrol, respectively) as well as cyano- and dicyano-vinyl electron-acceptor pendants were synthesized and developed for polymer solar cell (PSC) applications. The polymers covered broad absorption spectra of 400-800 nm with narrow optical bandgaps ranging 1.66-1.72 eV. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the polymers measured by cyclic voltommetry (CV) were found in the range of -5.12 to -5.32V and -3.45 to -3.55 eV, respectively. Under 100 mW/cm2 of AM 1.5 white-light illumination, bulk heterojunction (BHJ) photovoltaic devices comprising of an active layer of electron donor polymers (PCAZCN, PPTZCN, and PDTPCN) blended with electron-acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) in different weight ratios were investigated. The photovoltaic device containing donor PCAZCN and acceptor PC71BM in 1:2 weight ratio showed the highest power conversion efficiency (PCE) of 1.28 %, with Voc = 0.81 V, Jsc = 4.93 mA/cm2, and FF = 32.1%. In the fifth chapter a series of novel hydrogen-bonded (H-bonded) cross-linking polymers were generated by complexing various proton-donor (H-donor) solar cell dyes containing 3,6- and 2,7-functionalized electron-donating carbazole cores bearing symmetrical thiophene linkers and cyanoacrylic acid termini with a proton-acceptor (H-acceptor) side-chain homopolymer carrying pyridyl pendants (with 1/2 molar ratio of H-donor/H-acceptor). The supramolecular H-bonded structures between H-donor dyes and the H-acceptor side-chain polymer were confirmed by FTIR measurements. The effects of the supramolecular architecture on optical, electrochemical, and organic photovoltaic (OPV) properties were investigated. From DFT (density functional theory) calculations, the optimized geometries of organic dyes reflected that the carbazole cores of H-donor dyes were coplanar with the conjugated thiophenes and cyanoacrylic acids, which is essential for strong conjugations across the donor-acceptor units in D1-D4 dyes. Under 100 mW/cm2 of AM 1.5 white-light illumination, bulkheterojunction (BHJ) OPV cell devices containing an active layer of H-bonded polymers (PDFTP/D1-D4) as an electron donor blended with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as an electron acceptor in a weight ratio of 1:1 were explored. From the preliminary investigations, the OPV device containing 1:1 weight ratio of H-bonded polymer PDFTP/D2 and PCBM showed the best power conversion efficiency (PCE) value of 0.31% with a short-circuit current (Jsc) of 1.9 mA/cm2, an open-circuit voltage (Voc) of 0.55 V, and a fill factor (FF) of 29%, which has a higher PCE value than the corresponding H-donor D2 dye (PCE = 0.15%) or H-acceptor PDFTP homopolymer (PCE = 0.02%) blended with PCBM in 1:1 weight ratio.