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Turcu, Mircea Cassian. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1086247686828-95497.
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This work investigates the defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In1-xGax)(Se1-ySy)2 chalcopyrite thin films and the interrelationship with the alloy composition. Photoluminescence spectroscopy of investigated Cu-poor Cu(In,Ga)(Se,S)2 layers generally shows broad emission lines with the corresponding maxima shifting towards higher energies under decreasing temperature or under increasing excitation power. Admittance spectroscopy of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 chalcopyrite devices shows that the activation energies of the dominant defect distributions involving donors at the CdS/absorber interface and deep acceptors in the chalcopyrite bulk, increase upon alloying CuInSe2 with S. The band alignments within the Cu(In1-xGax)(Se1-ySy)2 system are determined using the energy position of the bulk acceptor state as a reference. The band gap enlargement under Ga alloying is accommodated almost exclusively in the rise of the conduction band edge, whereas the increase of band gap upon alloying with S is shared between comparable valence and conduction band offsets. The extrapolated band discontinuities [delta]EV(CuInSe2/CuInS2) = -0.23 eV, [delta]EC(CuInSe2/CuInS2) = 0.21 eV, [delta]EV(CuInSe2/CuGaSe2) = 0.036 eV, and [delta]EC(CuInSe2/CuGaSe2) = 0.7 eV are in good agreement with theoretical predictions. Current-voltage analysis of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 devices reveals recombination barriers which follow the band gap energy of the absorber irrespective of alloy composition, as expected for dominant recombination in the chalcopyrite bulk. In turn, the recombination at the active junction interface prevails in Cu-rich devices which display substantially smaller barriers when compared to the band gap energy of the absorber. The result indicates that the Cu-stoichiometry is the driving compositional parameter for the charge carrier recombination in the chalcopyrite heterojunctions under investigations.
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Turcu, Mircea Cassian. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys." Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A24342.
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This work investigates the defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In1-xGax)(Se1-ySy)2 chalcopyrite thin films and the interrelationship with the alloy composition. Photoluminescence spectroscopy of investigated Cu-poor Cu(In,Ga)(Se,S)2 layers generally shows broad emission lines with the corresponding maxima shifting towards higher energies under decreasing temperature or under increasing excitation power. Admittance spectroscopy of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 chalcopyrite devices shows that the activation energies of the dominant defect distributions involving donors at the CdS/absorber interface and deep acceptors in the chalcopyrite bulk, increase upon alloying CuInSe2 with S. The band alignments within the Cu(In1-xGax)(Se1-ySy)2 system are determined using the energy position of the bulk acceptor state as a reference. The band gap enlargement under Ga alloying is accommodated almost exclusively in the rise of the conduction band edge, whereas the increase of band gap upon alloying with S is shared between comparable valence and conduction band offsets. The extrapolated band discontinuities [delta]EV(CuInSe2/CuInS2) = -0.23 eV, [delta]EC(CuInSe2/CuInS2) = 0.21 eV, [delta]EV(CuInSe2/CuGaSe2) = 0.036 eV, and [delta]EC(CuInSe2/CuGaSe2) = 0.7 eV are in good agreement with theoretical predictions. Current-voltage analysis of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 devices reveals recombination barriers which follow the band gap energy of the absorber irrespective of alloy composition, as expected for dominant recombination in the chalcopyrite bulk. In turn, the recombination at the active junction interface prevails in Cu-rich devices which display substantially smaller barriers when compared to the band gap energy of the absorber. The result indicates that the Cu-stoichiometry is the driving compositional parameter for the charge carrier recombination in the chalcopyrite heterojunctions under investigations.
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Marginean, Camelia. "ENERGY BAND ALIGNMENTS AT METAL/MOLECULAR LAYER/SEMICONDUCTOR AND METAL/QUANTUM DOT INTERFACES USING BALLISTIC ELECTRON EMISSION MICROSCOPY." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243454379.
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Turcu, Mircea C. [Verfasser]. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys / Mircea C Turcu." Aachen : Shaker, 2004. http://d-nb.info/1170529550/34.
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Luo, Yandi. "Development of new buffer layers and rapid annealing process for efficient Sb₂Se₃ thin-film solar cells." Electronic Thesis or Diss., Université de Rennes (2023-....), 2024. http://www.theses.fr/2024URENS039.
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Dans ce travail de thèse, le comportement de l'interface de l'hétérojonction, le processus de croissance des grains cristallins et la couche tampon des cellules solaires à base de Sb₂2Se₃ ont été étudiés. La qualité de l'absorbeur et l'alignement des bandes d'énergie sont identifiés comme des paramètres clés pour réduire la densité de défauts et pour faciliter la séparation et le transport des porteurs de charge photogénérés. Une stratégie de dopage d'Al³⁺ dans la couche tampon de CdS a été introduite dans les cellules solaires Sb₂2Se₃. L'alignement des bandes d'énergie et la qualité de l'interface p-n ont été considérablement améliorés. Une courbure de bandes type "Spike-like" a été obtenue pour la meilleure cellule solaire avec un rendement de 8,41%. Deuxièmement, un procédé de recuit thermique rapide a également été développé et optimisé afin d'améliorer la qualité de la couche absorbeur de Sb₂2Se₃ avec une densité de défauts réduite. Le rendement des cellules solaires est augmenté à 9,03%. De plus, nous avons essayé de remplacer la couche tampon CdS toxique par un film ZnSnO respectueux de l'environnement avec en plus un band-gap plus large. Un rendement intéressant de 3,44% a été obtenue pour ces cellules solaires de Sb₂2Se₃ sans CdIn this thesis, heterojunction interface behavior, grain growth process and alternative buffer layer of Sb₂Se₃ based solar cells were investigated. The absorber quality and the band alignment are identified as key parameters for reducing defect density and for facilitating the separation and the transport of photogenerated charge carriers. A strategy of Al³⁺ doping into the CdS buffer layer was introduced in Sb₂Se₃ solar cells. The band alignment and the interface quality have been significantly improved. A “spike-like” structure was obtained for the best device with an efficiency of 8.41%. Secondly, a rapid thermal annealing process has also been developed and optimized in order to improve the quality of Sb₂Se₃ absorber film with reduced defect density. The efficiency of the Sb₂Se₃ solar cells is increased to 9.03%. In addition, we have tried to replace the toxic CdS buffer layer with an environmentally friendly ZnSnO film with moreover a wider band gap. An interesting power conversion efficiency of 3.44% was achieved for the Cd-free Sb₂Se₃ thin-film solar cells
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Reinhart, Christoph F. "Type II band alignment in Sl¦1¦-¦xGe¦x/Sl(001) quantum wells." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq24230.pdf.
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GIAMPIETRI, ALESSIO. "GROWTH, LOCAL STRUCTURAL AND ELECTRONIC PROPERTIES, AND BAND ALIGNMENT AT SRTIO3-BASED ALL-OXIDE HETEROJUNCTIONS." Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/476679.
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Recent advances in the growth of epitaxial oxide thin films have fostered a steady increase of research on oxide heterojunctions, which are now produced with unprecedented quality. Applications of these systems in the field of electronics, photovoltaics and photocatalysis strongly rely on the capability to master band gap engineering on the atomic scale. Strontium titanate (SrTiO3) is the substrate of choice commonly used in the production of all-oxide heterostructures, as in many cases these systems display a two dimensional electron gas (2DEG) confined at the interface, such as in the LaAlO3/SrTiO3 junction. The band offsets at the interface determine on which of the constituent materials the 2DEG will be confined, and provide additional information on the degree of confinement as well, so the study of the band alignment in oxide-based heterostructures is of crucial importance. Novel properties and functionalities can be achieved upon substitution of LaAlO3 with other oxide materials, an example being the BiFeO3 perovskite. In fact, BiFeO3 is a multiferroic material, and a complete control of the BiFeO3/SrTiO3 heterostructure may allow the tuning of the 2DEG at the interface through the application of an external electric or magnetic field. A 2DEG is also observed in the Al2O3/SrTiO3 junction, which show electron mobilities greater than those previously measured in perovskite-based heterojunctions. Despite in many structures the 2DEG is not observed, different interesting applications can still be obtained, such as in the CuO/SrTiO3 heterostructure, which is a promising material for the production of solar cells and for photoelectrochemical water splitting applications. The main objective of this work is to demonstrate the growth of high quality BiFeO3/SrTiO3, Al2O3/SrTiO3 and CuO/SrTiO3 heterostructures by off-axis sputtering, and to provide a detailed analysis of the interface properties. The band alignment at the interface is thus measured and discussed for each of these materials.
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Azemi, Elheme, and Saimir Bala. "Exploring BPM adoption and strategic alignment of processes at Raiffeisen Bank Kosovo." Jan vom Brocke, Jan Mendling, Michael Rosemann, 2019. http://epub.wu.ac.at/7176/1/paper4.pdf.
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Situation faced: Raiffeisen Bank Kosovo, as a subsidiary of Raiffeisen BankInternational AG, providesa wide range of banking products and services to all categories of customers in the private individual and business segments. In the first six months of 2018, the profit of the Bank was 11 Million Euro, being the highest in the banking market. The on-line banking channels has increased significantly and today the customers chose to do more than 80% of transactions through E-Banking, mobile phone,or ATMs. Raiffeisen Bank has started to adopt BPM since 2006 as a systemic and structured approach to analyze, improve, control, and manage processes with the aim to improve the quality of products and services. But, how well is BPM adapted and implemented in the bank, and what is the impact of BPM to the strategic goals? b)Action taken: This paper tackles the problem from two angles. First, a literature review is used to clarify the concept of BPM its scope. Second, semistructured interviews were used to collect data from nine participants covering high positions in Raiffeisen Bank Kosovo. In addition, the Research ffered both an evaluation of the significant aspects of the implementation process, and examinedthe key factors effects on alignment of BPM with organization strategy.
c)Results achieved: his study unveils that BPM is well understood and is con-sidered an important practice within the bank. Its implementation is familiar to the top management. Especially, process visualization is a considered a core element within BPM projects. Existing project can further benefit from BPM by applying process ownership and defining responsibilities within the end to end processes in every department were these processes are performed. Moreover, this study collects evidence that strategy objectives can be led by BPM. d)Lessons learned: Experience has taught that there are many challenges whenapplying BPM initiatives. However, once these are applied, they help achieving strategic objectives. Two main challenges of implementing BPM were related to lack of proper IT support and budget needed to cover staff training. This paper recommends that BPM initiatives be strategy driven. It should be treated in a holistic way, including several methodologies like Six Sigma, Lean, and Agile. In this way, the Bank is lead towards thinking how its product or services are delivered to the customers.
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Huang, Jianqiu. "First-Principles Study of Band Alignment and Electronic Structure at Metal/Oxide Interfaces: An Investigation of Dielectric Breakdown." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/95967.
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Oxide dielectric breakdown is an old problem that has been studied over decades. It causes power dissipations and irreversible damage to the electronic devices. The aggressive downscaling of the device size exponentially increases the leakage current density, which also raises the risk of dielectric breakdown. It has been proposed that point defects, current leakages, impurity diffusions, etc. all contribute to the change of oxide chemical composition and ultimately lead to the dielectric breakdown. However, the conclusive cause and a clear understanding of the entire process of dielectric breakdown are still under debate. In this research, the electronic structure at metal/oxide interfaces is studied using first-principle calculations within the framework of Density Functional Theory (DFT) to investigate any possible key signature that would trigger the dielectric breakdown.
A classical band alignment method, the Van de Walle method, is applied to the case study of the Al/crystal-SiO2 (Al/c-SiO2) interface. Point defects, such as oxygen vacancy (VO) and hydrogen impurity (IH), are introduced into the Al/c-SiO2 interface to study the effects on band offset and electronic structure caused by point defects at metal/oxide interfaces. It is shown that the bonding chemistry at metal/oxide interfaces, which is mainly ionic bond, polarizes the interface. It results in many interface effects such as the interface dipole, built-in voltage, band bending, etc. Charge density analysis also indicates that the interface can localize charge due to such ionic bonding. It is also found that VO at the interface traps metal electrons which closes the open -sp3 orbital. The analysis on local potential shows that the metal potential penetrates through a few layers of oxide starting from the interface, which metalizes the interfacial region and induces unoccupied states in the oxide band gap. In addition, it is shown that higher oxygen content at metal/oxide interfaces minimizes such metal potential invasion. In addition, an oxygen vacancy is created at multiple sites through the Al/c-SiO2 and Al/a-SiO2 interface systems, separately. The oxygen local pressure is also calculated before its removal using Quantum Stress Density theory. Correlations among electronic structure, stress density, and vacancy formation energy are found, which provide informative insights into the defect generation controlling and dielectric breakdown analysis.
A new band alignment approach based on the projection of plane-waves (PWs) into the space-dependent atomic orbital (LCAO) basis is presented and tested against classical band offset methods -- the Van de Walle method. It is found that the new band alignment approach can provide a quantitative and reliable band alignment and can be applied to the heterojunctions consisting of amorphous materials. The new band alignment approach reveals the real-space dependency of the electronic structure at interfaces. In addition, it includes all interface effects, such as the interface dipole, built-in voltage, virtual oxide thinning, and band deformation, which cannot be derived using classical band offset methods. This new band alignment approach is applied to the case study of both the Al/amorphous-SiO2 (Al/a-SiO2) interface and the Al/c-SiO2. We have found that at extremely low dimensions, the reduction of the insulator character due to the virtual oxide thinning is a pure quantum effect. I highlight that the quantum tunneling current leakage is more critical than the decrease of the potential barrier height on the failure of the devices.PHD
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Platzer-Björkman, Charlotte. "Band Alignment Between ZnO-Based and Cu(In,Ga)Se2 Thin Films for High Efficiency Solar Cells." Doctoral thesis, Uppsala universitet, Fasta tillståndets elektronik, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6263.
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Thin-film solar cells based on Cu(In,Ga)Se2 contain a thin buffer layer of CdS in their standard configuration. In order to avoid cadmium in the device for environmental reasons, Cd-free alternatives are investigated. In this thesis, ZnO-based films, containing Mg or S, grown by atomic layer deposition (ALD), are shown to be viable alternatives to CdS. The CdS is an n-type semiconductor, which together with the n-type ZnO top-contact layers form the pn-junction with the p-type Cu(In,Ga)Se2. From device modeling it is known that a buffer layer conduction band (CB) position of 0-0.4 eV above that of the Cu(In,Ga)Se2 layer is consistent with high photovoltaic performance. For the Cu(In,Ga)Se2/ZnO interface this position is measured by photoelectron spectroscopy and optical methods to –0.2 eV, resulting in increased interface recombination. By including sulfur into ZnO, a favorable CB position to Cu(In,Ga)Se2 can be obtained for appropriate sulfur contents, and device efficiencies of up to 16.4% are demonstrated in this work. From theoretical calculations and photoelectron spectroscopy measurements, the shift in the valence and conduction bands of Zn(O,S) are shown to be non-linear with respect to the sulfur content, resulting in a large band gap bowing. ALD is a suitable technique for buffer layer deposition since conformal coverage can be obtained even for very thin films and at low deposition temperatures. However, deposition of Zn(O,S) is shown to deviate from an ideal ALD process with much larger sulfur content in the films than expected from the precursor pulsing ratios and with a clear increase of sulfur towards the Cu(In,Ga)Se2 layer. For (Zn,Mg)O, single-phase ZnO-type films are obtained for Mg/(Zn+Mg) < 0.2. In this region, the band gap increases almost linearly with the Mg content resulting in an improved CB alignment at the heterojunction interface with Cu(In,Ga)Se2 and high device efficiencies of up to 14.1%.
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Platzer-Björkman, Charlotte. "Band alignment between ZnO-based and Cu(In,Ga)Se₂ thin films for high efficiency solar cells /." Uppsala : Acta Universitatis Upsaliensis : Universitetsbiblioteket [distributör], 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6263.
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Lohaus, Christian [Verfasser], Wolfram [Akademischer Betreuer] Jaegermann, and Oliver [Akademischer Betreuer] Clemens. "The Fermi Level in Hematite - Doping, Band Alignment, and Charge Transitions / Christian Lohaus ; Wolfram Jaegermann, Oliver Clemens." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2019. http://d-nb.info/1182537456/34.
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Wang, Jing. "Development of Graphitic Carbon Nitride based Semiconductor Photocatalysts for Organic Pollutant Degradation." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173216.
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As a potential solution to the global energy and environmental pollution, design and synthesis of artificial photocatalysts with high activities have attracted increasing scientific interests worldwide. In recent years, the graphitic carbon nitride (g-C3N4) has shown new possible applications in the photocatalytic field due to its unique properties. However, the photocatalytic efficiency of the pristine g-C3N4 is greatly limited by the high recombination rate of the photo-induced electron-hole pairs. In this thesis, the aim is to design and fabricate efficient g-C3N4 based photocatalysts with enhanced photocatalytic activities under a visible light irradiation. In order to achieve this goal, two strategies have been employed in the present thesis. First, the as-obtained g-C3N4 was used as the host material to construct staggered-aligned composite photocatalysts by selecting semiconductors with suitable band positions. By this method, three kinds of g-C3N4-based composite photocatalysts such as g-C3N4/ZnS nanocage, g-C3N4/m-Ag2Mo2O7 and g-C3N4/MIL-88A were successfully fabricated. Second, the microstructure of the g-C3N4 was modified by the H2O2-treatment at an elevated temperature and ambient pressure. In this study, the g-C3N4 was prepared by a simple pyrolysis of urea. As for all the as-synthesized phtocatalysts, the structures, morphologies and the optical properties were carefully characterized by the following techniques: XRD, SEM, TEM, FT-IR and DRS. Also, the band edge positions of m-Ag2Mo2O7 and MIL-88A were studied by the Mott-Schottky methods. Thereafter, the photocatalytic activities were evaluated by using a solution of rhodamine B (RhB) as a target pollutant for the photodegradation experiments performed under a visible light irradiation. The results showed that all the aforementioned g-C3N4-based photocatalysts exhibited enhanced photocatalytic activities in comparison with the pristine g-C3N4. For the case of the g-C3N4-based composite photocatalysts, the enhancement factor over the pristine g-C3N4 can achieve values ranging from 2.6 to 3.4. As for the H2O2-treated g-C3N4, the degradation rate constant can be 4.6 times higher than that of the pristine g-C3N4. To understand the key factors in new materials design, we also devote a lot of efforts to elucidate the basic mechanisms during the photocatalytic degradation of organic pollutant. Based on the results of the active species trapping (AST) experiments, the main active species in each photocatalytic system were determined. In the g-C3N4/m-Ag2Mo2O7 and the g-C3N4/MIL-88A system, three kinds of active species of ·O2-, h+ and ·OH were found to be involved in the photocatalytic reaction. Among them, the ·O2- and h+ were the main active species. In the g-C3N4/ZnS and H2O2-treated g-C3N4 photocatalytic systems, the main active species was determined as the ·O2-. The reaction pathways of these active species were also demonstrated by comparing the band edge positions with the potentials of the redox couple. In addition, the relationship between the active species and the photocatalytic behaviors of N-de-ethylation and conjugated structure cleavage were studied. Finally, possible mechanisms to explain the enhanced photocatalytic activities were proposed for each photocatalytic system. The results in this thesis clearly confirm that the photocatalytic activity of the g-C3N4 based photocatalyst can efficiently be enhanced by constructions of staggered-aligned composites and by modification of the microstructure of the g-C3N4. The enhanced photocatalytic performance can mainly be ascribed to the efficient separation of the photo-induced electron-hole pairs and the increase of the active sites for the photocatalytic reaction.QC 20150909
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Deyu, Getnet Kacha. "Defect Modulation Doping for Transparent Conducting Oxide Materials." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI071.
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Le dopage des matériaux semi-conducteurs est une partie fondamentale de la technologie moderne. Les oxydes conducteurs transparents (TCO) constituent une famille de semi-conducteurs, qui sont optiquement transparents et électriquement conducteurs. La conductivité électrique élevée est généralement obtenue grâce à un dopage associant des impuretés de substitution hétérovalentes comme dans In2O3 dopé au Sn (ITO), SnO2 dopé au fluor (FTO) et ZnO dopé à l'Al (AZO). Cependant, ces approches classiques ont dans de nombreux cas atteint leurs limites tant en ce qui concerne la densité de porteurs de charge atteignable, que pour la valeur de la mobilité des porteurs de charge. Le dopage par modulation est un mécanisme qui exploite l'alignement de la bande d'énergie à une interface entre deux matériaux pour induire une densité de porteurs de charges libres dans l’un d’entre eux ; un tel mécanisme a permis de montrer dans certains cas que la limitation liée à la mobilité pouvait ainsi était évitée. Cependant, la limite de densité de porteuse ne peut pas être levée par cette approche, du fait de l'alignement des limites de dopage par défauts intrinsèques. Le but de ce travail était de mettre en œuvre cette nouvelle stratégie de dopage pour les TCO. La stratégie repose sur l’utilisation de large bande interdite pour doper la surface des couches de TCO, ce qui résulte à un piégeage du niveau de Fermi pour la phase dopante et à un positionnement du niveau de Fermi en dehors de la limite de dopage dans les TCO. La méthode est testée en utilisant un TCO comme In2O3 non dopé, In2O3 dopé au Sn et SnO2 phase hôte et Al2O3 et SiO2-x en tant que phase de dopant gap à large bandeThe doping of semiconductor materials is a fundamental part of modern technology.Transparent conducting oxides (TCOs) are a group of semiconductors, which holds the features of being transparent and electrically conductive. The high electrical conductivity is usually obtained by typical doping with heterovalent substitutional impurities like in Sn-doped In2O3 (ITO), fluorine-doped SnO2 (FTO) and Al-doped ZnO (AZO). However, these classical approaches have in many cases reached their limits both in regard to achievable charge carrier density, as well as mobility. Modulation doping, a mechanism that exploits the energy band alignment at an interface between two materials to induce free charge carriers in one of them, has been shown to avoid the mobility limitation. However, the carrier density limit cannot be lifted by this approach, as the alignment of doping limits by intrinsic defects. The goal of this work was to implement the novel doping strategy for TCO materials. The strategy relies on using of defective wide band gap materials to dope the surface of the TCO layers, which results Fermi level pinning at the dopant phase and Fermi level positions outside the doping limit in the TCOs. The approach is tested by using undoped In2O3, Sn-doped In2O3 and SnO2 as TCO host phase and Al2O3 and SiO2−x as wide band gap dopant phase
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Venkatapathi, Sarankumar. "Temperature effects on the electronic properties of lead telluride (PbTe) and the influence of nano-size precipitates on the performance of thermoelectric materials. (SrTe precipitates in PbTe bulk material)." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/51947.
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This study seeks to evaluate the temperature effects on the electronic properties of thermoelectric materials, using first principles Density Functional Theory (DFT) calculations by incorporating the temperature effects on structural properties of the material. Using the electronic properties attained, the charge carrier scattering relaxation times were determined. The effect of interface between PbTe and SrTe on the charge carrier mobility was studied by finding out the relative alignment of energy bands at the semiconductor heterojunction. The crystal shape of the SrTe precipitates in the PbTe host matrix was evaluated from the interface energies using the Wulffman construction. We also attempted to develop a relation between the interface energies and electronic band alignment for different interface orientations.
In this research, we incorporated the temperature effects on the structural properties of PbTe to get the temperature dependence of electronic properties like energy bandgap and effective masses of charge carriers. We used the values of bandgap and effective masses to determine the charge carrier scattering relaxation time at different temperatures which is used in evaluating the transport properties of thermoelectric materials like the Seebeck coefficient and electrical conductivity.Master of Science
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Tom, Anas. "Physical Layer Algorithms for Interference Reduction in OFDM-Based Cognitive Radio Systems." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5872.
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Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier transmission scheme used in most of the existing wireless standards such as LTE, WiFi and WiMAX. The popularity of OFDM stems from the multitude of benefits it offers in terms of providing high data rate transmission, robustness against multipath fading and ease of implementation. Additionally, OFDM signals are agile in the sense that any subcarrier can be switched on or off to fit the available transmission bandwidth, which makes it well suited for systems with dynamic spectrum access such as cognitive radio systems. Nonetheless, and despite all the aforementioned advantages, OFDM signals have high spectral sidelobes outside the designated band of transmission, that can create severe interference to users in adjacent transmission bands, particularly when there is no synchronization between users. The focus of this dissertation is to propose baseband solutions at the Physical Layer (PHY) of the communications system to address the interference resulting from the high out-of-band (OOB) emissions of OFDM.
In the first part of this dissertation, we propose a precoder capable of generating mask compliant OFDM signals with low OOB emissions that are always contained under a given spectrum emission mask (SEM) specified by the OFDM standard. The proposed precoder generates transmitted signals with bit error rate (BER) performance similar to that of classical OFDM and does not reduce the spectral efficiency of the system.
In the second part of this dissertation, we introduce a novel and elegant approach, called suppressing alignment (SA), to jointly reduce the OOB interference and peak-to-average power ratio (PAPR) of OFDM systems. SA exploits the unavoidable redundancy provided by the CP as well as the wireless communications channel to generate an OOB/PAPR suppressing signal at the OFDM transmitter. Furthermore, after passing through the wireless channel, the suppressing signal is aligned with the CP duration at the OFDM receiver, essentially causing no interference to the data portion of the OFDM symbol. The proposed approach improves the PAPR of the transmitted OFDM signal and reduces the OOB interference by tens of decibels. Additionally, the proposed approach maintains an error performance similar to that of plain OFDM without requiring any change in the receiver structure of legacy OFDM.
In order to reduce the spectral emissions of OFDM, additional blocks, such as linear precoders, are usually introduced in the transmitter leading to a transmitted signal that is drastically different than that of a classical OFDM signal. This distortion is typically quantified by the error vector magnitude (EVM), a widely used metric specified by the wireless standard and is directly related to the BER performance of the system. The receiver can usually decode the information data with acceptable error probabilities if the distortion introduced to the transmitted signal is below the EVM values specified in the OFDM standard. Linear precoders, while capable of achieving significant reduction in the OOB interference, they typically introduce large distortion to the transmitted signal. As such, the receiver needs to know the precoding done at the transmitter to be able to recover the data which usually entails sending large amount of side information that can greatly reduce the spectral efficiency of the system. In the last part of this dissertation, we target the design of precoders for the purpose reducing the OOB interference, in a transparent manner where the receiver does not need to know the changes introduced in the transmitter. We present two precoders capable of significantly reducing the OOB emissions while producing transmitted signals with EVM values below those specified by the wireless standard, thereby guaranteeing acceptable error performance.
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SALVINELLI, GABRIELE. "PROBING OXIDE HETEROSTRUCTURE INTERFACES THROUGH ANGLE RESOLVED AND RESONANT ELECTRON SPECTROSCOPIES." Doctoral thesis, Università degli Studi di Milano, 2015. http://hdl.handle.net/2434/262157.
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In the recent years, electronic devices have become smaller and faster, as well as more powerful and efficient. However, the size of the building blocks of the current electronics - i.e. the transistors - is quickly approaching the limits of manufacture. The need of a new generation of devices based on novel mechanisms is today essential. In this scenario, well-defined interfaces between oxide materials have produced novel electronic systems displaying a spectacular variety of properties with promising potentialities for future devices, such as colossal magnetoresistance, high-temperature superconductivity, magnetism at the interface between non magnetic oxides, as well as two-dimensional electron gas between two oxide insulators. Indeed, interfaces between perovskite oxides - e.g. the LaAlO3/SrTiO3 – have shown properties at the nanometer scale that are qualitatively different from their single building blocks, allowing one to engineer novel functionalities through the growth of epitaxial heterostructures. Nevertheless, both atomic and electronic reconstructions could be present in oxide interfaces when a polar discontinuity occurs at the junction and the possibility to probe non-destructively the cation depth profiles can provide further insight into the oxide heterointerface physics. This is also true for less-ordered systems - i.e. amorphous thin films - which are playing a key role in the development of new architectures in photovoltaic applications, such as the CdxSnyOz/TiO2 heterojunction. In this Thesis, the combination of chemical and structural information on a local scale (i.e. at the interface and the nearby few atomic layers) has been obtained by combining an effective modeling of angle-resolved x-ray photoemission data, with synchrotron based electron spectroscopy techniques. It is shown how in oxides the interfacial electronic properties can be driven by complex substitutional effects across the interface, such as stoichiometry gradients, cation vacancies and interdiffusion, as well as by the presence of interfacial/surface oxygen vacancies.
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Galindo, Muñoz Natalia. "Development of direct measurement techniques for the in-situ internal alignment of accelerating structures." Doctoral thesis, Universitat Politècnica de València, 2018. http://hdl.handle.net/10251/100488.
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Las exigentes tolerancias de alineación en los componentes de los futuros colisionadores lineales de partículas requieren el desarrollo de nuevas técnicas de alineación más precisas que las existentes. Este es el caso del Colisionador Lineal Compacto (Compact Linear Collider, CLIC), cuyos objetivos altamente restrictivos de alineamiento alcanzan los 10 um. Para poder lograr el máximo rendimiento del acelerador, es necesario que el posicionamiento de las estructuras que aceleran las partículas y de los campos que las guían cumplan las tolerancias de alineación para dirigir el haz a lo largo de la trayectoria diseñada. Dicho procedimiento consiste en relacionar la posición de los ejes de referencia de cada componente con respecto a objetos externos, o fiduciales, lo cual resulta muy tedioso y económicamente costoso. Los errores sistemáticos y aleatorios se van acumulando en cada paso del proceso y, en consecuencia, la precisión final de alineamiento es todo un desafío. En este contexto, nace el proyecto PACMAN (Particle Accelerator Components Metrology and Alignment to the Nanometre scale), subvencionado por la Unión Europea en el programa FP7 de financiación para la investigación e innovación. El objetivo principal de PACMAN es investigar, desarrollar e implementar una solución integrada alternativa que incorpore todos los pasos de alineación en una misma ubicación, con el objetivo de mejorar la precisión de alineación de los componentes de los aceleradores, en concreto: las estructuras aceleradoras, los cuadrupolos y los monitores de posición de haz. La viabilidad de las soluciones desarrolladas y la precisión de alineamiento alcanzada deben de demostrarse en un banco de pruebas utilizando componentes de CLIC. La estrategia de PACMAN para alcanzar el objetivo técnico se divide en tres pasos. El primero consiste en la fiducialización de los componentes y sus soportes. El segundo paso es el ensamblaje de los componentes en dos tipos de soporte, uno compuesto por un monitor de posición de haz y un cuadrupolo, y otro con cuatro estructuras aceleradoras, tomando como referencia su centro electromagnético. Finalmente, ambos soportes se transportan al túnel para su alineación final utilizando técnicas de hilos tensados. En esta tesis doctoral, se describe el desarrollo de una nueva técnica no destructiva para localizar los ejes electromagnéticos de estructuras aceleradoras y su validación experimental. Para ello, se ha utilizado una estructura aceleradora de CLIC conocida como TD24. Debido a la complejidad mecánica de la TD24, su difícil acceso y su diámetro medio de iris de 5.5 mm, se desarrolla una nueva técnica denominada en esta tesis como 'el método perturbativo' y se realiza una propuesta experimental de validación. El estudio de viabilidad de este método, cumpliendo con los requisitos impuestos de precisión en la medida de 10 um, ha sido realizado con una campaña extensa de simulaciones de campos electromagnéticos en tres dimensiones utilizando la herramienta de software conocida como HFSS. Los resultados de simulación han permitido el desarrollo de un algoritmo muy completo de medidas y han proporcionado las especificaciones técnicas para el diseño conceptual de un banco de pruebas para la medida de los ejes electromagnéticos de la TD24. El preciso ensamblaje del banco de pruebas y sus correspondientes calibraciones, la incorporación de nuevos tratamientos de las medidas en el algoritmo final y la caracterización de fuentes de error en la medida, favorecieron la localización del centro electromagnético en la TD24 con una precisión menor a 1 um con un error estimado menor que 8.5 um, cumplimiendo con los objetivos de precisión establecidos.In the next generation of linear particle accelerators, challenging alignment tolerances are required in the positioning of the components focusing, accelerating and detecting the beam over the accelerator length in order to achieve the maximum machine performance. In the case of the Compact Linear Collider (CLIC), accelerating structures, beam position monitors and quadrupole magnets need to be aligned in their support with respect to their reference axes with an accuracy of 10 um. To reach such objective, the PACMAN (Particle Accelerator Components Metrology and Alignment to the Nanometer Scale) project strives for the improvement of the current alignment accuracy by developing new methods and tools, whose feasibility should be validated using the major CLIC components. This Ph.D. thesis concerns the investigation, development and implementation of a new non-destructive intracavity technique, referenced here as 'the perturbative method', to determine the electromagnetic axes of accelerating structures by means of a stretched wire, acting as a reference of alignment. Of particular importance is the experimental validation of the method through the 5.5 mm iris-mean aperture CLIC prototype known as TD24, with complex mechanical features and difficult accessibility, in a dedicated test bench. In the first chapter of this thesis, the alignment techniques in particle accelerators and the novel proposals to be implemented in the future linear colliders are introduced, and a detailed description of the PACMAN project is provided. The feasibility study of the method, carried out with extensive electromagnetic fields simulations, is described in chapter 2, giving as a result, the knowledge of the theoretical accuracy expected in the measurement of the electromagnetic axes and facilitating the development of a measurement algorithm. The conceptual design, manufacturing and calibration of the automated experimental set-up, integrating the solution developed to measure the electromagnetic axes of the TD24, are covered in chapter 3. The future lines of research and developments of the perturbative method are also explored. In chapter 4, the most significant results obtained from an extensive experimental work are presented, analysed and compared with simulations. The proof-of-principle is completed, the measurement algorithm is optimised and the electromagnetic centre is measured in the TD24 with a precision less than 1 um and an estimated error less than 8.5 um. Finally, in chapter 5, the developments undertaken along this research work are summarised, the innovative achievements accomplished within the PACMAN project are listed and its impact is analysed.
En la generació pròxima d'acceleradors de partícules lineals, desafiant toleràncies d'alineament és requerit en el posicionament dels components que enfoquen, accelerant i detectant la biga sobre la longitud d'accelerador per tal d'aconseguir l'actuació de màquina màxima. En el cas del Colisionador Compacte Lineal (CLIC), accelerant estructures, monitors de posició de fes i imants necessiten ser alineats en el seu suport amb respectar a les seves destrals de referència amb una precisió de 10 um. Per assolir tal objectiu, el PACMAN (Metrologia de Components de l'Accelerador de partícules i Alineament al Nanometer Escala) projecte s'esforça per la millora de l'actual precisió d'alineament per mètodes nous en desenvolupament i eines, la viabilitat dels quals hauria de ser validada utilitzant els components de CLIC importants. Aquesta tesi concerneix la investigació, desenvolupament i implementació d'un nou no-destructiu tècnica interna, va referenciar ací mentre 'el mètode de pertorbació' per determinar les destrals electromagnètiques d'accelerar estructures mitjançant un cable estès, actuant com a referència d'alineament. De la importància particular és la validació experimental del mètode a través del 5.5 mm iris-roí obertura prototipus de CLIC sabut com TD24, amb característiques mecàniques complexes i accessibilitat difícil, en un banc de prova dedicat. En el primer capítol d'aquesta tesi, les tècniques d'alineament en acceleradors de partícules i les propostes novelles per ser implementades en el futur colisionador lineal és introduït, i una descripció detallada del projecte PACMAN és proporcionat. L'estudi de viabilitat el mètode de pertorbació, va dur a terme amb simulacres de camps electromagnètics extensos, és descrit dins capitol 2, donant com a resultat, el coneixement de la precisió teòrica esperada en la mida de les destrals electromagnètiques i facilitant el desenvolupament d'un algoritme de mida. El disseny conceptual, fabricació i calibratge del conjunt experimental automatitzat-amunt, integrant la solució desenvolupada per mesurar les destrals electromagnètiques del TD24, és cobert dins capitol 3. Les línies futures de recerca i desenvolupaments del mètode és també va explorar. Dins capitol 4, la majoria de resultats significatius van obtenir d'una faena experimental extensa és presentada, analitzat i comparat amb simulacres. La prova-de-el principi és completat, l'algoritme de mida és optimitzat i el centre electromagnètic és mesurat en el TD24 amb una precisió menys d'1 um i un error calculat menys de 8.5 um. Finalment, dins capitol 5, els desenvolupaments empresos al llarg d'aquesta faena de recerca és resumit, les consecucions innovadores van acomplir dins del projecte PACMAN és llistat i el seu impacte és analitzat.
Galindo Muñoz, N. (2018). Development of direct measurement techniques for the in-situ internal alignment of accelerating structures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/100488
TESIS
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Richter, Jan Hinnerk. "Electronic Properties of Metal Oxide Films Studied by Core Level Spectroscopy." Doctoral thesis, Uppsala : Uppsala universitet, Fakultetsövergripande enheter, Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7180.
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Shirinda, Obed. "Studying chirality in a ~ 100, 130 and 190 mass regions." Thesis, University of the Western Cape, 2011. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_8742_1319096308.
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Chirality is a nuclear symmetry which is suggested to occur in nuclei when the total angular momentum of the system has an aplanar orientation [Fra97, Fra01]. It can occur for nuclei with triaxial shape, which have valence protons and neutrons with predominantly particle and hole nature. It is expected that the angular momenta of an odd particle and an odd hole (both occupying high-j orbitals) are aligned predominantly along the short and the long axes of the nucleus respectively, whereas the collective rotation occurs predominantly around the intermediate axis of a triaxially deformed nucleus in order to minimize the total energy of the system. Such symmetry is expected to be exhibited by a pair of degenerate DI = 1 rotational bands, i.e. all properties of the partner bands should be identical. The results suggested that spin independence of the energy staggering parameter S(I ) within two-quasiparticle chiral bands (previously suggested a fingerprint of chirality) is found only if the Coriolis interaction can be completely neglected. However, if the configuration is nonrestricted, the Coriolis interaction is often strong enough to create considerable energy staggering. It was also found that staggering in the intra- and inter-band B(M1) reduced transition probabilities (proposed as another fingerprint of chirality) may be a result of effects other than strongly broken chirality. Therefore, the use of the B(M1) staggering as a fingerprint of strongly broken chiral symmetry seems rather risky, in particular if the phase of the staggering is not checked.
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Sterner, Jan. "ALD Buffer Layer Growth and Interface Formation on Cu(In,Ga)Se2 Solar Cell Absorbers." Doctoral thesis, Uppsala universitet, Fasta tillståndets elektronik, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4009.
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Cu(In,Ga)Se2 (CIGS) thin film solar cells contain a thin layer of CdS. To avoid toxic heavy-metal-containing waste in the module production the development of a cadmium-free buffer layer is desirable. This thesis considers alternative Cd-free buffer materials deposited by Atomic Layer Deposition (ALD). Conditions of the CIGS surface necessary for ALD growth are investigated and the heterojunction interface is characterized by band alignment studies of ZnO/CIGS and In2S3/CIGS interfaces. The thesis also includes investigations on the surface modification of the CIGS absorber by sulfurization. According to ALD theory the growth process is limited by surface saturated reactions. The ALD growth on CIGS substrates shows nucleation failure and generally suffers from surface contaminations of the CIGS layer. The grade of growth disturbance varies for different ALD precursors. The presence of surface contaminants is related to the substrate age and sodium content. Improved growth behavior is demonstrated by different pretreatment procedures. The alignment of the energy bands in the buffer/absorber interface is an important parameter for minimization of the losses in a solar cell. The valence band and conduction band offsets was determined by in situ X-ray and UV photoelectron spectroscopy during layer by layer formation of buffer material. The conduction band offset (ΔEc) should be small but positive for optimal solar cell electrical performance according to theory. The conduction band offset was determined for the ALD ZnO/CIGS interface (ΔEc = -0.2 eV) and the ALD In2S3/CIGS interface (ΔEc = -0.25 eV). A high temperature process for bandgap grading and a low temperature process for surface passivation by post deposition sulfurization in H2S were investigated. It is concluded that the high temperature sulfurization of CuIn(1-x)GaxSe2 leads to phase separation when x>0. The low temperature process did not result in enhanced device performance.
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Madani, Sepideh Sadat. "Investigation of charge transport metal oxides for efficient and stable perovskite solar cells." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/235892/1/Sepideh%2BSadat%2BMadani%2BThesis%282%29.pdf.
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This research investigates various thin-film metal oxides as charge transport layer for improving the performance and stability of perovskite solar cells. Physical Vapor Deposition techniques such as magnetron sputtering, and electron beam evaporation were used to fabricate the metal oxide thin films. The structural, morphological, chemical, optical, electrical, and electronic properties of the films were studied. Solar Cell Capacitance Simulator was employed for investigating the performance of the PSC using the experimental data as input parameters. Results showed that optimized properties of the metal oxide thin films as charge (hole) transport layer have improved the performance of the PSC device.
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Ghimire, Harishchandra. "Structure, Dynamics, and Distance Measurements in Membrane Proteins and Peptides using EPR Spectroscopic Techniques." Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1291739688.
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Bittau, Francesco. "Analysis and optimisation of window layers for thin film CDTE solar cells." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/32642.
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The work presented in this thesis focuses on the investigation and improvement of the window stack of layers for thin film CdTe solar cells fabricated in the Center for Renewable Energy Systems Technology (CREST) laboratories. In particular the aim was to change the standard structure including TCO, high resistive transparent (HRT)layer and CdS which is limited by the low transparency of the CdS layer, to a better performing one. The first result chapter of the thesis describes the study of ZnO HRT layers. ZnO thin films were deposited by radio frequency (RF) magnetron sputtering with different structural, optical and electrical properties which were characterized by X-ray diffraction, electron microscopy, spectrophotometry, Hall Effect method and 4-point probe. ZnO films were then incorporated in CdTe solar cells with the structure: FTO/ZnO/CdS/CdTe/Au back contact and the performance of these devices were compared with the film properties to single out trends and identify optimal film characteristics. By varying the deposition pressure of ZnO films, it was possible to increase their transparency and significantly increase their resistivity. While better transparency positively affected the solar cell current density output and efficiency, the resistivity of ZnO films did not show any clear impact on device efficiency. By increasing the deposition temperature the ZnO film grain size was increased. Increased FF was observed in devices incorporating ZnO layers with bigger grains, although this gain was partially counterbalanced by the Voc degradation, leading to a limited efficiency improvement. Finally the addition of oxygen had the main effect of increasing the resistivity of ZnO films, similarly to what happened with the increase of the sputtering pressure. In this case however, an improvement of FF, Jsc and efficiency was observed, especially at an O2/Ar ratio of 1%. By simulating the solar cells behavior with SCAPS-1D, it was found that these performance change can be explained by the variation of interface properties, precisely the amount of interface defects, rather than by bulk properties. The study presented in the second result chapter focuses on magnesium-doped zinc oxide (MZO) and the variation of its energy band structure. MZO was initially used as the HRT layer within a solar cell structure: FTO/MZO/CdS/CdTe/Au back contact. Sputtering MZO films with a target containing MgO 11 weight% and ZnO 89 weight% allowed for and increased band gap from 3.3 eV of intrinsic ZnO to 3.65 eV for MZO deposited at room temperature. Increasing the superstrate deposition temperature allowed for a further band gap increase up to 3.95 eV at 400 °C due mainly to an conduction band minimum upward shift. It was highlighted the importance to create a positive conduction band offset with the MZO layer conduction band slightly above the CdS conduction band, with an optimum found in this case to be 0.3 eV (efficiency 10.6 %). By creating a positive conduction band offset all the performance parameters (Voc, FF, Jsc, efficiency) significantly increased. One of the reasons for this improvement was found to be a diminished interface recombination due to a more ideal MZO/CdS band alignment. In the second part of this investigation the MZO was used as a replacement for the CdS in a simplified structure: FTO/MZO/CdTe/Au back contact. The concepts used to optimise the performance of these devices also involved tuning the conduction band alignment between MZO/CdTe and efficiencies of 12.5 % were achieved with a at conduction band offset. The efficiency increase was achieved mainly thanks to a better transparency of the MZO layer and a higher Jsc output, compared to devices using a CdS buffer layer. The MZO buffers have been tested in combination with different TCOs. Results are presented in the third result chapter and showed that AZO is a good alternative to FTO working effectively in combination with MZO. AZO/MZO efficiency thin film CdTe solar cells (12.6%, compared to 12.5% with FTO). It was found that increasing the IR transparency of the TCOs leads to a potentially higher Jsc. Achieving a better transparency was obtained by using TCOs with high mobility and lower carrier concentration (AZO and ITiO) and also by using a boro-aluminosilicate glass with low iron content. ITiO yielded the best opto-electrical properties among all the TCO materials. Devices incorporating ITiO however, showed lower performance then those using FTO and AZO. ITO/MZO windows also yielded poor performance. In addition, the ITO films deposited had a high carrier concentration leading to a high NIR absorption by plasma resonance and resulted not ideal for application in thin film CdTe PV.
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Jama, Mariel Grace. "Semiconductor composites for solid-state lighting." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0207/document.
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Phases organiques luminescentes qui sont incorporés dans une matrice inorganique conductrice est proposé dans cette étude pour la couche active d'une diode émettant de la lumière hybride. Dans ce composite, le colorant organique joue le rôle de site de recombinaison radiative de porteurs de charge qui sont injectées dans la matrice de transport ambipolaire inorganique. Comme l'un des combinaisons de matériaux de candidat, bicouche et des films minces composites de ZnSe et un complexe d'iridium rouge (Ir(BPA)) émetteur de lumière organique ont été préparé in situ par UHV technique d'évaporation thermique. Les alignements de bande d'énergie mesurée par spectroscopie de photoélectrons (PES) pour le ZnSe/Ir(BPA)et deux couches de ZnSe+Ir(BPA) révèlent que le composite HOMO et LUMO du colorant organique sont positionnées dans la largeur de bande interdite de ZnSe. Cette gamme offre les forces motrices énergiques nécessaires pour les transferts d'électrons et de trous de ZnSe à Ir(BPA). Par l'interprétation des données du PES,la composition chimique des interfaces ont également été déterminés. Le ZnSe/Ir(BPA) interface est réactive, même si elle est d'une pureté de matériaux de haute.Pendant ce temps, l'Ir (BPA)/ZnSe interface ne présente pas la pureté matériel. Ceci est représenté à la nature de ZnSe évaporation comme Zn particuliers et des fluxSE2, associée à des interactions chimiques avec le Ir(BPA) substrat. L'interface est,de ce fait, composé d'une multitude de phases, les phases de Se0, ZnSe rares, réduit Se et oxydé molécules de colorant, et de Zn qui sont intercalées atomes dans leIr(BPA) substrat. PES des composites ZnSe+Ir(BPA) révèle des tendances similaires à l'Ir(BPA)/ZnSe interface. A des émissions de lumière rouge surfaciques et intermittents fanées ont été observés à partir de dispositifs qui incorporent couches alternées séquences de ZnSe et Ir(BPA) pour la couche activeLuminescent organic phases that are embedded in a conductive inorganicmatrix is proposed in this study for the active layer of a hybrid light-emitting diode. Inthis composite, the organic dye acts as the radiative recombination site for chargecarriers that are injected into the inorganic ambipolar transporting matrix. As one ofthe candidate material combinations, bilayer and composite thin films of ZnSe and ared iridium complex (Ir(BPA)) organic light emitter were prepared in situ via UHVthermal evaporation technique. The energy band alignments measured byphotoelectron spectroscopy (PES) for the ZnSe/Ir(BPA) bilayer and ZnSe+Ir(BPA)composite reveal that the HOMO and LUMO of the organic dye are positioned in theZnSe bandgap. This lineup provides the required energetic driving forces for electronand hole transfers from ZnSe to Ir(BPA). By interpreting PES data, the chemicalcomposition of the interfaces were also determined. The ZnSe/Ir(BPA) interface isreactive even though it is of high material purity. Meanwhile, the Ir(BPA)/ZnSeinterface does not exhibit material purity. This is accounted to the nature of ZnSeevaporation as individual Zn and Se2 fluxes, coupled with chemical interactions withthe Ir(BPA) substrate. The interface is, thereby, composed of an abundance of Se0phases, sparse ZnSe phases, reduced Se and oxidized dye molecules, and Znatoms that are intercalated into the Ir(BPA) substrate. PES of the ZnSe+Ir(BPA)composites reveals similar trends to the Ir(BPA)/ZnSe interface. A faded areal andintermittent red light emissions were observed from devices that incorporatedalternating layer sequences of ZnSe and Ir(BPA) for the active layer
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Hermans, Yannick. "Interface analysis and development of BiVO4 and CuFeO2 heterostructures for photochemical water splitting." Phd thesis, Bordeaux, 2019. http://tuprints.ulb.tu-darmstadt.de/8700/1/Complete_thesis%20-%20German.pdf.
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Solar photo(electro)chemical (PEC) water splitting is regarded as a promising ways of renewable hydrogen production. Especially, type 2 PEC systems, in which the necessary energy needed to split water can be supplied by two complimentary photoabsorbers, have the potential to economically compete with steam methane reforming, the conventional hydrogen production method. In this work, BiVO4 and CuFeO2 were chosen to perform the water oxidation and water reduction reaction, respectively. However, according to literature additional contact materials are required to achieve a reasonable water splitting performance.
The exact benefits of these contact materials have not yet been completely elucidated. Therefore, we opted in this work to investigate the junction properties of certain BiVO4 and CuFeO2 based heterostructures through so called interface experiments, whereby a certain contact material was stepwise sputtered onto a BiVO4 or CuFeO2 substrate, performing photoelectron spectroscopy measurements in between each deposition step. In this way we could interpret the band
alignment between the substrate and the contact material, as well as determine the Fermi level tunability for the studied photoabsorbers.
In parallel, new anisotropic CuFeO2 and BiVO4 based heterostructured powders were created through photodeposition. In particular, silver, platinum, cobalt(oxy)(hydr)oxide and nickel(oxy)(hydr)oxide were successfully deposited onto anisotropically shaped BiVO4 and CuFeO2 powders. These powders were tested as well for their performance in photochemical water splitting.
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Uddin, Md Tamez. "Metal oxide heterostructures for efficient photocatalysts." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00879226.
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Photocatalytic processes over semiconducting oxide surfaces have attracted worldwide attention aspotentially efficient, environmentally friendly and low cost methods for water/air purification as well as forrenewable hydrogen production. However, some limitations to achieve high photocatalytic efficiencies havebeen found due to the fast recombination of the charge carriers. Development of heterostucture photocatalystsby depositing metals on the surface of semiconductors or by coupling two semiconductors with suitable bandedge position can reduce recombination phenomena by vectorial transfer of charge carriers. To draw newprospects in this domain, three different kinds of heterostructures such as n-type/n-type semiconductor(SnO2/ZnO), metal/n-type semiconductor (RuO2/TiO2 and RuO2/ZnO) and p-type/n-type semiconductor(NiO/TiO2) heterojunction nanomaterials were successfully prepared by solution process. Their composition,texture, structure and morphology were thoroughly characterized by FTIR, X-ray diffraction (XRD), Ramanspectroscopy, transmission electron microscopy (TEM) and N2 sorption measurements. On the other hand, asuitable combination of UV-visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy(XPS) and ultraviolet photoemission spectroscopy (UPS) data provided the energy band diagram for eachsystem. The as-prepared heterojunction photocatalysts showed higher photocatalytic efficiency than P25 TiO2for the degradation of organic dyes (i.e. methylene blue and methyl orange) and the production of hydrogen.Particularly, heterostructure RuO2/TiO2 and NiO/TiO2 nanocomposites with optimum loading of RuO2 (5 wt %)and NiO (1 wt %), respectively, yielded the highest photocatalytic activities for the production of hydrogen.These enhanced performances were rationalized in terms of suitable band alignment as evidenced by XPS/UPSmeasurements along with their good textural and structural properties. This concept of semiconductingheterojunction nanocatalysts with high photocatlytic activity should find industrial application in the future toremove undesirable organics from the environment and to produce renewable hydrogen.
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Zu, Fengshuo. "Electronic properties of organic-inorganic halide perovskites and their interfaces." Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/20396.
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Über die besonders hohe Effizienz von Halid-Perowskit (HaP)-basierten optoelektronischen Bauteilen wurde bereits in der Literatur berichtet. Um die Entwicklung dieser Bauteile voranzutreiben, ist ein umfassendes und verlässliches Verständnis derer elektronischen Struktur, sowie der Energielevelanordnung (ELA) an HaP Grenzflächen von größter Bedeutung. Demzufolge beschäftigt sich die vorliegende Arbeit mit der Untersuchung i) der Bandstruktur von Perowskit-Einkristallen, um ein solides Fundament für die Darlegung der elektronischen Eigenschaften von polykristallinen Dünnschichten zu erarbeiten, und mit ii) den Einflüssen von Oberflächenzuständen auf die elektronische Struktur der Oberfläche, sowie deren Rolle bei der Kontrolle von ELA an HaP Grenzflächen. Die Charakterisierung erfolgt überwiegend mithilfe von Photoelektronenspektroskopie (PES) und ergänzenden Messmethoden wie Beugung niederenergetischer Elektronen an Oberflächen, UV-VIS-Spektroskopie, Rasterkraftmikroskopie und Kelvin-Sonde.
Erstens weist die Banddispersion von zwei prototypischen Perowskit-Einkristallen eine starke Dispersion des jeweiligen oberen Valenzbandes (VB) auf, dessen globales Maximum in beiden Fällen am R-Punkt in der Brillouin-Zone liegt. Dabei wird eine effektive Lochmasse von 0.25 m0 für CH3NH3PbBr3, bzw. von ~0.50 m0 für CH3NH3PbI3 bestimmt. Basierend auf diesen Ergebnissen werden die elektronischen Spektren von polykristallinen Dünnschichten konstruiert und es wird dadurch aufgezeigt, dass eine Bestimmung der Valenzbandkantenposition ausgehend von einer logarithmischen Intensitätsskala aufgrund von geringer Zustandsdichte am VB Maximum vorzuziehen ist.
Zweitens stellt sich bei der Untersuchung der elektronischen Struktur von frisch präparierten Perowskit-Oberflächen heraus, dass die n-Typ Eigenschaft eine Folge der Bandverbiegung ist, welche durch donatorartige Oberflächenzustände hervorgerufen wird. Des Weiteren weisen die PES-Messungen an Perowskiten mit unterschiedlichen Zusammensetzungen aufgrund von Oberflächenphotospannung eine Anregungslichtintensitätsabhängigkeit der Energieniveaus von bis zu 0.7 eV auf. Darüber hinaus wird die Kontrolle von ELA durch gezielte Variation der Oberflächenzustandsdichte gezeigt, wodurch sich unterschiedliche ELA-Lagen (mit Abweichungen von über 0.5 eV) an den Grenzflächen mit organischen Akzeptormolekülen erklären lassen. Die vorliegenden Ergebnisse verhelfen dazu, die starke Abweichung der in der Literatur berichteten Energieniveaus zu erklären und somit ein verfeinertes Verständnis des Funktionsprinzips von perowskit-basierten Bauteilen zu erlangen.Optoelectronic devices based on halide perovskites (HaPs) and possessing remarkably high performance have been reported. To push the development of such devices even further, a comprehensive and reliable understanding of their electronic structure, including the energy level alignment (ELA) at HaPs interfaces, is essential but presently not available. In an attempt to get a deep insight into the electronic properties of HaPs and the related interfaces, the work presented in this thesis investigates i) the fundamental band structure of perovskite single crystals, in order to establish solid foundations for a better understanding the electronic properties of polycrystalline thin films and ii) the effects of surface states on the surface electronic structure and their role in controlling the ELA at HaPs interfaces. The characterization is mostly performed using photoelectron spectroscopy, together with complementary techniques including low-energy electron diffraction, UV-vis absorption spectroscopy, atomic force microscopy and Kelvin probe measurements. Firstly, the band structure of two prototypical perovskite single crystals is unraveled, featuring widely dispersing top valence bands (VB) with the global valence band maximum at R point of the Brillouin zone. The hole effective masses there are determined to be ~0.25 m0 for CH3NH3PbBr3 and ~0.50 m0 for CH3NH3PbI3. Based on these results, the energy distribution curves of polycrystalline thin films are constructed, revealing the fact that using a logarithmic intensity scale to determine the VB onset is preferable due to the low density of states at the VB maximum. Secondly, investigations on the surface electronic structure of pristine perovskite surfaces conclude that the n-type behavior is a result of surface band bending due to the presence of donor-type surface states. Furthermore, due to surface photovoltage effect, photoemission measurements on different perovskite compositions exhibit excitation-intensity dependent energy levels with a shift of up to 0.7 eV. Eventually, control over the ELA by manipulating the density of surface states is demonstrated, from which very different ELA situations (variation over 0.5 eV) at interfaces with organic electron acceptor molecules are rationalized. Our findings further help to explain the rather dissimilar reported energy levels at perovskite surfaces and interfaces, refining our understanding of the operational principles in perovskite related devices.
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Wu, Ming-Yuan, and 吳明遠. "Investigating the interfacial band alignments at Hf-based gate dielectrics." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/79182881037102906352.
Full textAbstract:
碩士中國文化大學
材料科學與奈米科技研究所
97
The trend of shrinking gate dielectric thickness rapidly in device, the tunneling effect generates a great leakage current. According to this reason, the conventional material (SiO2) which used at gate dielectric has to replace. Hafnium is considered as the compatible candidate to replace the silicon dioxide. The advantage of hafnium dielectric not only has high permittivity but also the better effect oxide thickness (EOT) value. This paper studies three different hafnium materials： HfO2, HfSiO and HfSiON. The thin film was manufactured by using metal organic CVD (MOCVD). During the different RTA temperatures, discussed the thin film thermal stability and structure characteristic. XRD and XPS analyzed the crystal structure and chemical bonding respectively. TEM observed the interfacial quality between hafnium and silicon substrate. MIS capacitor structure expresses the electric characterization to discuss the influence of device in different annealing temperature, which promoted the interfacial layer by using the C-V, I-V curve analysis. In conclusion, the thermal stability of HfSiO and HfSiON are better than HfO2. Although, the permittivity of HfSiO and HfSiON decreasing, but due to the defect density of thin film is small, which modified the leakage current tunneling effect. The interfacial layer emerged from the three types material, doping silicon atom can restrain the interfacial layer growth effectively.
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Lin, Shang-Ren, and 林上仁. "Determination of Band Alignments at the Interfaces of TMDC Vertical Heterostructures Using Soft X-ray Photoemission Spectromicroscopy." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/jftsb3.
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Turcu, Mircea Cassian [Verfasser]. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys / von Mircea Cassian Turcu." 2004. http://d-nb.info/971826161/34.
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Ku, Yi Hang, and 辜翊航. "Band alignment studies of graphene/ZnO and MoS2/WS2 heterostuctures." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/57973252544563615533.
Full textAbstract:
碩士國立清華大學
先進光源科技學位學程
104
In this study, we focus on 2D material interface and measured the band structure by Scanning Photo-Electron Microscopy (SPEM) at National Synchrotron Radiation Research Center (NSRRC). The experiment with two topics: (1) Graphene/ZnO heterojunction, and (2) MoS2/WS2 heterostructures. From the topic (1), we found ZnO with flat band structure contact to the interface, and it was quite different from the results of Schottky contact in literature. In topic (2), we compared two MoS2/WS2 hetero- structures with different bonding at the interface (Van der Waals bond and covalent bond), and we found the structures have distinct band structure properties. With these new results, we believe it will contribute to the application of two-dimensional materials in the future. Keywords: 2D material, band structure, X-ray photoelectron spectroscopy, graphene, transition-metal dichalcogenide
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Chiu, Ming-Hui. "Band Alignment Determination of Two-Dimensional Heterojunctions and Their Electronic Applications." Diss., 2018. http://hdl.handle.net/10754/627889.
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Two-dimensional (2D) layered materials such as MoS2 have been recognized as high on-off ratio semiconductors which are promising candidates for electronic and optoelectronic devices. In addition to the use of individual 2D materials, the accelerated field of 2D heterostructures enables even greater functionalities. Device designs differ, and they are strongly controlled by the electronic band alignment. For example, photovoltaic cells require type II heterostructures for light harvesting, and light-emitting diodes benefit from multiple quantum wells with the type I band alignment for high emission efficiency. The vertical tunneling field-effect transistor for next-generation electronics depends on nearly broken-gap band alignment for boosting its performance. To tailor these 2D layered materials toward possible future applications, the understanding of 2D heterostructure band alignment becomes critically important.
In the first part of this thesis, we discuss the band alignment of 2D heterostructures. To do so, we firstly study the interlayer coupling between two dissimilar 2D materials. We conclude that a post-anneal process could enhance the interlayer coupling of as-transferred 2D heterostructures, and heterostructural stacking imposes similar symmetry changes as homostructural stacking. Later, we precisely determine the quasi particle bandgap and band alignment of the MoS2/WSe2 heterostructure by using scan tunneling microscopy/spectroscopy (STM/S) and micron-beam X-ray photoelectron spectroscopy (μ-XPS) techniques. Lastly, we prove that the band alignment of 2D heterojunctions can be accurately predicted by Anderson’s model, which has previously failed to predict conventional bulk heterostructures.
In the second part of this thesis, we develop a new Chemical Vapor Deposition (CVD) method capable of precisely controlling the growth area of p- and n-type transition metal dichalcogenides (TMDCs) and further form lateral or vertical 2D heterostructures. This method also allows p- and n-type TMDCs to separately grow in a selective area in one step. In addition, we demonstrate a first bottom-up 2D complementary inverter based on hetero-TMDCs.
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Lohaus, Christian. "The Fermi Level in Hematite - Doping, Band Alignment, and Charge Transitions." Phd thesis, 2019. https://tuprints.ulb.tu-darmstadt.de/8541/1/Lohaus_2019_final.pdf.
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In this work the position of the Fermi level in hematite (Fe2O3) is being manipulating and the accessible range of Fermi level positions within the optical band gap is being determined. This range directly translates to the photovoltage that a semiconducting material like Fe2O3 can generate and thereby gives an answer why usually the photovoltages of hematite based devices fall short of predicted values based on the value of the optical band gap.
In order to study the Fermi level position of RF-magnetron sputtered hematite thin films the samples were being investigated by XPS and UPS without leaving the UHV conditions in advance, thus guarantying clean surfaces. The phase and other structural properties of the thin films after deposition and manipulation were investigated by Raman spectroscopy and XRD. Optical transmission and reflectance measurements and electrical investigations gave insight into the functional properties of the thin films.
The manipulation of the position of the Fermi level was achieved with several techniques. First, by utilizing a self-designed co-sputtering setup, doping elements were incorporated during the sputter deposition into the hematite thin films. The doping elements of choice were the p-type dopant magnesium as well as the n-type dopants silicon and zirconium.
In addition, manipulation of the Fermi level was achieved by contact formation on the surface of hematite thin films. Dedicated interface experiments to materials such as ITO, RuO2, Al2O3, and NiO gave further insight into the accessible Fermi level positions. Finally, the behavior of the Fermi level in hematite while being in contact with molecular species (oxygen, water, OH-, peroxides) was being studied as well.
The results show accessible Fermi level positions from 0.3eV to 1.75eV above the valence band maximum. This range of about 1.5 eV is far less than the optical band gap which is about 2.2 eV and is in good agreement with the low photovoltages that are usually reported for hematite (or other transition metal oxides) based devices.
The upper value of 1.75 eV was achieved by several different techniques and is identified to be a fundamental limit to the Fermi level due to pinning. The origin of this pinning is found to be the charge transition from Fe3+ to Fe2+. In other words, instead of generating free charge carriers in the conduction band the electrons are being trapped at an iron site and are positioned much lower in energy.
This trapping has already been discussed in literature as polarons and has been identified to be the leading cause for slow charge carrier transport. This work extents the understanding of polarons in hematite and other transition metal oxides by identifying these quasi-particles as reasons for energetic limitations preventing large photovoltages.
In addition, it was shown that the polaron state which is positioned within the optical band gap of hematite acts as an effective band edge. Using the results from interface experiments a new assignment of the band edge position on an absolute energy scale is possible and it is shown that electrochemical Mott-Schottky plot analysis have positioned the band edges too low. However, charge transfer from hematite to the hydrogen redox level in water is still not possible as the electrons are trapped within the lower lieing polaron state.
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Hsu, Feng-Chang, and 許峰菖. "Carrier dynamics and band alignment of GaAsSb Capped InAs Quantum Dots." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/34864449947347294953.
Full textAbstract:
碩士國立交通大學
電子物理系所
99
The optical properties of GaAsSb-capped InAs quantum dots (QDs) with different capping layer thickness are investigated. Both the emission energy and the recombination lifetime of the QDs are found to be correlated with the capping layer thickness. Theoretical calculations based on eight-band model indicates that the quantum confinement of hole states and their wave function distributions are sensitive to the GaAsSb capping layer thickness. The Sb induced structural changes in QDs are also found to play a significant role in the optical properties of GaAsSb-capped QDs. We show that controlling the GaAsSb capping layer thickness is a feasible way to tailor the InAs QDs for long-wavelength applications. Then, we study the recombination dynamics in the InAs/GaAs0.84Sb0.16 QDs. In this type-II QDs system, the radiative transitions are strong affected by the band-bending effect induced by the carriers accumulated at the type-II InAs/GaAs0.84Sb0.16 interface. After the laser pulse excitation, the QD emission exhibits strong transition rate variations and large energy redshifts. Here we use the energy dependent TRPL to map the whole QD emission spectrum. After analysis the time evolution of peak energy and peak intensity, we can get the time evolution of the intensity and the energy shift. We report up to 2.1 times transition rate enhancement in the annealed type-II InAs/GaAs0.84Sb0.16 QDs could be achieved by high injection power. We find that the transition energy shows a linear dependence with the 2/3th power of the total emission intensity, indicating the QD emission obeys the type-II transition. Consequently, we can control the transition type in the InAs/GaAs0.84Sb0.16 QDs by the different injection levels. Finally, we study the electro-optical characteristics of type-II QDs embedded in PIN structure. We use photocurrent experiment to study the absorption spectra and the carrier escape processes in the type-II QDs. Then we study the effect of applied electric field on the emission properties of type-II QDs.
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Peng, Chuan-Ming, and 彭權銘. "Band Alignment Type of the SiGe/Si Heterojunction Determined by Electro-Luminescence." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/73413836548890118169.
Full textAbstract:
碩士國立臺灣大學
電子工程學研究所
94
The advantage of the optical electronic component made up by silicon and germanium materials is that it could be fully compatible with the Si-based microelectronic chips. Therefore, the cost of the fabrication could decrease. In addition, the growth techniques for quantum heterojunction structures are in advanced and then the heterojunction structure of silicon or germanium has been studied far and wide recently. In this study, the light-emitting diodes (LEDs) with multi-periods of Si/SiGe superlattice structures are used. The ten periods Si/SiGe superlattice structure are grown by UHV/CVD system and two materials of Si and Si0.9Ge0.1bulk materials which works as capping layer are grown in the P+ doped region. The two samples are called the Si0.9Ge0.1 capping and the Si capping respectively. The study starts by the measurements of the EL spectra and the LI curves. Then, the optical characteristics of the light emitting diode is got and discussed. This discussion is focused on the Si light emission from the buffer layer. Then, by the discussion, the band structure at the boundary between the Si buffer layer and the Si0.9Ge0.1 capping layer is discussed. Finally, a stable and reliable studying framework would be established.
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Al, Sulami Ahmad. "A First Principle Investigation of Band Alignment in Emerging III-Nitride Semiconductors." Thesis, 2020. http://hdl.handle.net/10754/662679.
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For more than seventy years, semiconductor devices have functioned as the cornerstone for technological advancement, and as the defining transition into the information age. The III-Nitride family of semiconductors, in particular, underwent an impressive maturation over the past thirty years, which allowed for efficient light- emitting devices, photo-detectors, and power electronic devices.
As researchers try to push the limits of semiconductor devices, and in particular, as they aim to design ultraviolet light emitters and high threshold power devices, the search for new materials with high band gaps, high breakdown voltages, unique optical properties, and variable lattice parameters is becoming a priority. Two interesting candidates that can help in achieving the aforementioned goals are the wurtzite BAlN and BGaN alloy systems, which are currently understudied due to difficulties associated with their growth in epitaxial settings.
In our research, we will investigate the band alignment between BAlN and BGaN alloys, and other wurtzite III-Nitride semiconductors from first principle simulations. Through an understanding of band alignment types and a quantification of the band offset values, researchers will be able to foresee the applicability of a particular interface. As an example, a type-I band alignment with a high conduction band offset and a low
valence band offset is a potential electron blocking layer to be implemented in standard LED designs.
This first principle investigation will be aided by simulations using Density Functional Theory (DFT) as implemented in the Vienna Ab Initio Simulation Package (VASP) environment. In addition, we will detail an experiment from the literature that uses X- ray Photoelectron Spectroscopy on multiple samples to infer and quantify the band alignment between different materials of interest to us. We aim in this study to anticipate the band alignment in interfaces involving materials at the cutting edge of research. Our hope is to set a theoretical ground for future experimental studies on this same matter in parallel to the current efforts to improve the quality and stability of wurtzite BAlN and BGaN alloy crystals.
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Chan, Ming-Hui, and 詹明蕙. "Direct evidence of type II band alignment in ZnO nanorods/P3HT heterostructures." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/89410221796248366194.
Full textAbstract:
碩士國立臺灣大學
應用物理所
99
In this thesis, the emission from ZnO/P3HT heterostructures with type II band alignment has been investigated, analyzed and discussed. The photoluminescence (PL) emission around 950 nm can be found and attributed to the type II transition related to the recombination of electrons in conduction band of ZnO and holes in highest occupied molecular orbital (HOMO of P3HT). Power-dependent PL spectra exhibiting a blue-shift with the increasing excitation power offer one of the evidences on the type II transition. In addition, lifetime of P3HT measured by using time-resolved photoluminescence (TRPL) also strongly supports that the infrared light indeed arises from the type II transition. It is found that the lifetime of P3HT in ZnO/P3HT heterostructrue (396 ps) is much shorter than that of pure P3HT film (613 ps). Therefore, our measurements provide the first direct evidence of the type II band alignment in ZnO/P3HT heterostructure.
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Smith, Noah Harold. "Alignment filtering of ICESat flight data." 2012. http://hdl.handle.net/2152/19483.
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ICESat consisted of the Geoscience Laser Altimeter System (GLAS) and a commercial spacecraft bus. The stability of the GLAS to bus alignment was unknown and significant for GLAS pointing. Pointing control was performed by the bus, and variations of the GLAS alignment were effectively pointing control errors. There were four star trackers making measurements sensitive to this alignment, two on GLAS and two on the bus. Tracker pointing variations during samples from seven years of flight data were estimated using an alignment filter. The states of an alignment filter represent multiple independent attitudes, enabling the fusion of measurements from an arbitrary number of trackers and gyro units. The ICESat alignment filter states were equivalent to four tracker pointing vectors, expressed in both the body and celestial frames. Together with a star catalog, the four pointing vectors were equivalent to predictions of the tracker measurements. The stars provided nearly ideal reference points, but filter performance was improved by detecting and handling deterministic star errors. The primary result was evidence for relatively large pointing variations of the two GLAS trackers, on the order of fifty arcseconds, with both periodic orbital variations and trends on long time scales. There was also evidence of correlations between the variations of the two GLAS trackers, suggesting that they reflected GLAS to bus alignment variations.text
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Tsai, Chung-Lin, and 蔡宗霖. "The Study on the Band Alignment and Characterizationof GaAsSb/GaAs Quantum Well Lasers." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/60234027793066686362.
Full textAbstract:
碩士國立臺灣大學
電子工程學研究所
93
In the past decade, many research groups reported their valence band offset ratio (Qv0) for GaAsSb/GaAs system, but no common consensus is made yet. In this study, we propose a novel method to determine the valence band offset ratio by comparing the wavelength- cavity length relation of a GaAs0.64Sb0.36/GaAs single quantum well laser with a self-consistent solution. The determined valence band offset ratio and bowing parameter are Qv0 = 1.02 and bg = -1.31 eV respectively. In this calculation, we also found that when the carrier density is low, the dominant transition is from electron excited state to hole ground state. Only when the carrier density is high enough to form the band bending, electron ground state becomes the dominant transition level. Simulation results also show that spontaneous recombination does not dominate the characteristic temperature of our laser. A new quantum well structure with narrow GaAs barrier is analyzed. The simulation shows that the structure can enhance the coupling between electron and heavy hole wavefunctions. It may reduce the threshold current density, and further, improve the characteristic temperature, as long as the strain can be accommodated by the lattice.
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Wang, Li-Hong, and 王力弘. "Observation of Band Alignment at WSe2-MoSe2 Lateral Heterojunction by Scanning Tunneling Microscopy." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/g5vn3f.
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碩士國立臺灣大學
應用物理研究所
106
Graphene has catched a lot of attention since it was proved to be two-dimensional material. It has plenty of intresting properties such as high carrier mobility, superier thermal conductivity, fexibility, transconductances, and so on. The lack of bandgap and complex preparation to open the bandgap of graphene make it less attractive when the two-dimensional transition metal dichalcogenides (2-d TMDCs) was discovered. Some of the TMDCs are semiconductor and has suitable bandgap which would influence the on-o↵ ratio in field effect transistor (FET). We would reveal the band alignment of single layer WSe2-MoSe2 lateral heterojunction on highly oriented pyrolytic graphite (HOPG), and the band width in the WSe2-MoSe2 boundary by scanning tunneling microscopy. The moir´e pattern of TMDCs denotes that there is an angle around 7 between layers. The band offset and the built-in electric field are calculated. The bandgaps of WSe2 and MoSe2 are 2.04 eV and 2.16 eV. The band o↵set of conduction band and valence band are 0.26 eV and 0.37 eV. At the heterojunction boundary, we observed a transition width up to 3.58 nm with a built-in electric field of about 7.7x107 V/m. These properties expand the field of photonic and electrical devices.
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"Interface Electronic State Characterization of Plasma Enhanced Atomic Layer Deposited Dielectrics on GaN." Doctoral diss., 2014. http://hdl.handle.net/2286/R.I.24827.
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abstract: In this dissertation, the interface chemistry and electronic structure of plasma-enhanced atomic layer deposited (PEALD) dielectrics on GaN are investigated with x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). Three interrelated issues are discussed in this study: (1) PEALD dielectric growth process optimization, (2) interface electronic structure of comparative PEALD dielectrics on GaN, and (3) interface electronic structure of PEALD dielectrics on Ga- and N-face GaN. The first study involved an in-depth case study of PEALD Al2O3 growth using dimethylaluminum isopropoxide, with a special focus on oxygen plasma effects. Saturated and self-limiting growth of Al2O3 films were obtained with an enhanced growth rate within the PEALD temperature window (25-220 ºC). The properties of Al2O3 deposited at various temperatures were characterized to better understand the relation between the growth parameters and film properties. In the second study, the interface electronic structures of PEALD dielectrics on Ga-face GaN films were measured. Five promising dielectrics (Al2O3, HfO2, SiO2, La2O3, and ZnO) with a range of band gap energies were chosen. Prior to dielectric growth, a combined wet chemical and in-situ H2/N2 plasma clean process was employed to remove the carbon contamination and prepare the surface for dielectric deposition. The surface band bending and band offsets were measured by XPS and UPS for dielectrics on GaN. The trends of the experimental band offsets on GaN were related to the dielectric band gap energies. In addition, the experimental band offsets were near the calculated values based on the charge neutrality level model. The third study focused on the effect of the polarization bound charge of the Ga- and N-face GaN on interface electronic structures. A surface pretreatment process consisting of a NH4OH wet chemical and an in-situ NH3 plasma treatment was applied to remove carbon contamination, retain monolayer oxygen coverage, and potentially passivate N-vacancy related defects. The surface band bending and polarization charge compensation of Ga- and N-face GaN were investigated. The surface band bending and band offsets were determined for Al2O3, HfO2, and SiO2 on Ga- and N-face GaN. Different dielectric thicknesses and post deposition processing were investigated to understand process related defect formation and/or reduction.Dissertation/Thesis
Ph.D. Physics 2014
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Correia, Luís Miguel Ribeiro. "Hybrid equalization techniques for heterogeneous systems in the millimeter wave band." Master's thesis, 2021. http://hdl.handle.net/10773/32345.
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With the constant demand for better service and higher transmission rates current technologies are reaching the limits of the channel capacity. Although, technologies such as MIMO and Heterogeneous systems appear to increase the channel capacity by introducing more antennas at the transceivers making the link between users and base station more reliable. Furthermore, the current spectrum, sub-6GHz, is becoming saturated and due to the properties of such frequencies the deployment of heterogeneous systems can introduce some levels of interference. Towards improving future communication systems a new part of the frequencies spectrum available should be used, researchers have their eyes on the mmWave band. This band allows to increase the carrier frequency and respective signal bandwidth and therefore increase the transmission speeds, moreover the properties of such frequencies unlock some advantages over the frequencies used in the sub-6G band. Additionally, mmWave band can be combined with massive MIMO technology to enhance the system capacity and to deploy more antenna elements in the transceivers. One more key technology that improves the energy efficiency in systems with hundreds of antenna elements is the possibility to combine analog and digital precoding techniques denoted as hybrid architectures. The main advantages of such techniques is that contrary to the full digital precoding processing used in current systems this new architecture allows to reduce the number of RF chains per antenna leading to improved energy efficiency.
Furthermore to handle heterogeneous systems that have small-cells within the macro-cell, techniques such as Interference Alignment (IA) can be used to efficiently remove the existing multi-tier interference.
In this dissertation a massive MIMO mmWave heterogeneous system is implemented and evaluated. It is designed analog-digital equalizers to efficiently remove both the intra an inter-tier interference. At digital level, an interference alignment technique is used to remove the interference and increase the spectral efficiency. The results showed that the proposed solutions are efficient to remove the macro and small cells interference.Com a constante procura de melhores serviços e taxas de transmissão mais elevadas, as tecnologias atuais estão a atingir os limites de capacidade do canal. Contudo tecnologias como o MIMO e os sistemas heterogéneos permitem aumentar a capacidade do canal através da introdução de mais antenas nos transcetores e através da implementação de pequenos pontos de acesso espalhados pela célula primária, com o intuito de tornar as ligações entre os utilizadores e a estação base mais fiáveis. Tendo também em atenção que o espectro atual, sub-6GHz, está sobrecarregado e que devido às propriedades das frequências utilizadas a implementação de sistemas heterogéneos pode levar a níveis de interferência insustentáveis. Por modo a resolver esta sobrecarga futuros sistemas de comunicação devem aproveitar uma maior parte do espectro de frequências disponível. A banda das ondas milimétricas (mmWave) tem sido apontada como solução, o que permite aumentar a frequência utilizada para transportar o sinal e consequentemente aumentar as velocidades de transmissão. Uma outra vantagem da banda mmWave é que pode ser combinada com a tecnologia MIMO massivo, permitindo implementar mais elementos de antena nos terminais e consequentemente aumentar a capacidade do sistema. Umas das tecnologias desenvolvida para melhorar a eficiência energética em sistemas com centenas de antenas é a possibilidade de combinar técnicas de codificação analógica e digital, designadas como arquiteturas híbridas. A principal vantagem desta técnica é que, contrariamente ao processamento feito nos sistemas atuais, totalmente no domínio digital, esta nova arquitetura permite reduzir o número de cadeias RF por antena. Com o intuito de reduzir a interferência em sistemas heterogéneos, técnicas como o alinhamento de interferência são usadas para separar utilizadores das células secundárias dos utilizadores das células primárias de modo a reduzir a interferência multi-nível existente no sistema geral. Nesta dissertação, é implementado e avaliado um sistema heterogéneo que combina MIMO massivo e ondas milimétricas. Este sistema é projetado com equalizadores analógico-digitais para remover com eficiência a interferência intra e inter-camadas. No domínio digital é utilizada a técnica de alinhamento de interferência para remover a interferência e aumentar a eficiência espectral. Os resultados mostram que as soluções propostas são eficientes para remover a interferência entre as células secundárias e a primária.
Mestrado em Engenharia Eletrónica e Telecomunicações
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Chetty, Daniel. "Optimisation of the alignment of business and credit functions in the private bank segment in a South African bank." Diss., 2008. http://hdl.handle.net/2263/23813.
Full textAbstract:
Currently the sales and credit departments of Private Banks have divergent business objectives. The sales department’s primary objective is to sell the bank’s products and generate revenue through new business acquisition, while the credit department’s objective is to balance risk and reward by ensuring that capital is deployed in the most effective manner. In the private bank department of the bank that was studied, these divergent objectives have led to inefficiencies in the business processes and have promoted the silo-based operations, which impact the customer experience negatively. Several strategies for future implementation were identified in order to optimise the alignment between the sales and credit functions of the private banking department of the bank. The strategies were categorised into customer centricity, relationship pricing, alignment of personal key performance indicators, addressing of system inefficiencies and exploring various alternate strategies (e.g. strategies that aim to achieve a better understanding of each others’ roles and work pressures better; improving communication; aligning their goals; working towards supporting the success of each department). It was found that there was a strong alignment of the views of the private bank staff (credit and sales viewed as a group) towards the future strategies. When the views of the credit staff were compared with the views of the sales staff, it was found that there was alignment of the opinions of the two departments on the futures strategies that could be implemented to allow credit and sales to work more effectively together.Dissertation (MBA)--University of Pretoria, 2010.
Gordon Institute of Business Science (GIBS)
unrestricted
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Ramesha, A. "Sub-Threshold Slope Modeling & Gate Alignment Issues In Tunnel Field Effect Transistor." Thesis, 2008. https://etd.iisc.ac.in/handle/2005/792.
Full textAbstract:
The Tunnel Field Effect Transistor (TFET) with sub-60mV/decade Sub-threshold slope and extremely high ION/IOFF ratio has attracted enough attention for low standby power (LSTP) applications where the battery life is very important. So far research in this area has been limited to numerical simulation and experimental analysis. It is however extremely necessary to develop compact models for TFET in order to use them in nano-scale integrated circuit design and simulation. In this work, for the first time, we develop analytical Sub-threshold slope model for n-channel double gate TFET (nDGTFET). Unlike conventional FETs, current in TFET is mainly controlled by the band-to-band tunneling mechanism at source/channel interface. As the total drain current is proportional to band-to-band generation rate, the main challenge in the present work is to find an explicit relationship between average electric field over the tunneling path and the applied gate voltage under nonlocal tunneling condition. Two dimensional Poisson’s equation (with Laplace approximation)is first solved in a rectangular coordinate system in order to obtain analytical expression for electron energy distribution over the channel region.Kane’s Model[J. Phy. Chem.Solids 12(181)1959]for band-to-band tunneling along with some analytical approximation techniques are then used to derive the expression for the Sub-threshold slope under nonlocal tunneling conditions. This Sub-threshold slope model is verified against professional numerical device simulator (MEDICI) for different device geometries.
Being an asymmetric device, TFET fabrication suffers from source misalignment with gate. As the doping in source and drain-gate are different, conventional-FET-like self-aligned gate stack formation is not possible for TFET. Such misalignment, at source side, seriously degrades the performance of TFETs. To overcome this problem, in this work we explore the possibility of using “gate replacement” technique for TFET fabrication. We first develop process flow for single gate bulk nTFET, and then we extend it to n-channel double gate TFET (nDGTFET) using modified FinFET process. Good alignments between source and gate are observed with TCAD-simulations in both the cases.
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Ramesha, A. "Sub-Threshold Slope Modeling & Gate Alignment Issues In Tunnel Field Effect Transistor." Thesis, 2008. http://hdl.handle.net/2005/792.
Full textAbstract:
The Tunnel Field Effect Transistor (TFET) with sub-60mV/decade Sub-threshold slope and extremely high ION/IOFF ratio has attracted enough attention for low standby power (LSTP) applications where the battery life is very important. So far research in this area has been limited to numerical simulation and experimental analysis. It is however extremely necessary to develop compact models for TFET in order to use them in nano-scale integrated circuit design and simulation. In this work, for the first time, we develop analytical Sub-threshold slope model for n-channel double gate TFET (nDGTFET). Unlike conventional FETs, current in TFET is mainly controlled by the band-to-band tunneling mechanism at source/channel interface. As the total drain current is proportional to band-to-band generation rate, the main challenge in the present work is to find an explicit relationship between average electric field over the tunneling path and the applied gate voltage under nonlocal tunneling condition. Two dimensional Poisson’s equation (with Laplace approximation)is first solved in a rectangular coordinate system in order to obtain analytical expression for electron energy distribution over the channel region.Kane’s Model[J. Phy. Chem.Solids 12(181)1959]for band-to-band tunneling along with some analytical approximation techniques are then used to derive the expression for the Sub-threshold slope under nonlocal tunneling conditions. This Sub-threshold slope model is verified against professional numerical device simulator (MEDICI) for different device geometries.
Being an asymmetric device, TFET fabrication suffers from source misalignment with gate. As the doping in source and drain-gate are different, conventional-FET-like self-aligned gate stack formation is not possible for TFET. Such misalignment, at source side, seriously degrades the performance of TFETs. To overcome this problem, in this work we explore the possibility of using “gate replacement” technique for TFET fabrication. We first develop process flow for single gate bulk nTFET, and then we extend it to n-channel double gate TFET (nDGTFET) using modified FinFET process. Good alignments between source and gate are observed with TCAD-simulations in both the cases.
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Bin, Yang. "Business-IT alignment from operational level: empirical evidence from the Bank of Qingdao, China." Doctoral thesis, 2020. http://hdl.handle.net/10071/24929.
Full textAbstract:
Business-IT Alignment (BITA) has long been a significant topic for scholars as well as enterprise managers especially in the Internet era. Although numerous studies have identified the factors influencing the aligning process and relationships between them and organization successes from strategic perspective, few consider the impact of these elements on employees’s performances from an operational level. To fill this gap, this thesis first discusses the state-of-art and the challenges of BITA in China’s city commercial banks (CCBs) and further develops a theoretical framework to empirically evaluate the BITA in China banking industry. Finally, some recommendations for improving the level of BITA in China’s CCBs are provided.
Taking the Bank of Qingdao (BQD) as a sample, this thesis empirically examines BITA maturity model with the results that five factors including communication, IT competency/value measurement, IT governance, partnership, and IT skills are positively related to the BITA while IT scope and architecture are not significant. In addition, the moderating effect of service quality between BITA and employee’s working performance is also supported by the survey. This study also develops a new theoretical model namely, business-IT punctuated equilibrium alignment model (BIPEAM), based on life cycle theory and punctuated equilibrium theory to describe the alternately leading roles between business and IT strategies. This model may contribute towards the better understanding of the mechanism of business-IT strategic alignment process from a longitudinal perspective within an enterprise.O alinhamento entre o negócio e as Tecnologias de Informação (TI) ou alinhamento business-IT (BITA) tem sido desde há muito um tópico significativo para académicos bem como para gestores de empresas, especialmente na era da Internet. Embora numerosas investigações tenham identificado os fatores que influenciam o processo de alinhamento e as relações entre eles e os sucessos da organização do ponto de vista estratégico, poucas consideram o impacto destes elementos no desempenho dos empregados a partir de um nível operacional. Para preencher esta lacuna, esta tese começa por discutir o estado da arte e os desafios do BITA nos bancos comerciais das cidades da China (CCBs) e desenvolve um quadro teórico para avaliar empiricamente o BITA na indústria bancária Chinesa. Por último, são fornecidas algumas recomendações para melhorar o nível de BITA nos CCBs da China. Tomando o Banco de Qingdao (BQD) como amostra, esta tese examina empiricamente o modelo de maturidade do BITA com os resultados de que cinco fatores, incluindo comunicação, competência/avaliação de TI, governação de TI, parceria, e competências de TI estão positivamente relacionados com o BITA enquanto que o âmbito e a arquitetura de TI não são significativos. Além disso, o efeito moderador da qualidade do serviço entre a BITA e o desempenho de trabalho do empregado é também apoiado pelo inquérito realizado. Este estudo também desenvolve um novo modelo teórico, nomeadamente o modelo de alinhamento de equilíbrio pontuado de business-IT (BIPEAM) baseado na teoria do ciclo de vida e na teoria do equilíbrio pontuado para descrever os papéis alternadamente de liderança entre as estratégias empresariais e de TI. Este modelo pode contribuir para uma melhor compreensão do mecanismo do processo de alinhamento estratégico entre empresas e as TI, a partir de uma perspetiva longitudinal dentro de uma empresa.
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Chen, Wei-Guang, and 陳韋光. "The Effect of Mechanical Strain and Band Alignment at the Anatase-Rutile Interface on the Photocatalytic Activity of TiO2." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/27214522204362057359.
Full textAbstract:
碩士國立臺灣大學
材料科學與工程學研究所
102
TiO2 is considered as one of the most important photocatalysts to date primarily due to many of its superior physical and chemical properties. Among its various polymorphs, rutile and anatase TiO2 are the two most important phases and have been widely used in many practical applications. However, due to its relatively large band gap, only a small portion of the solar spectrum in the ultraviolet light region can be absorbed to excite electrons to generate photocurrents for use in photocatalytic reactions. To further improve its performance, many research efforts have been made to increase its photocatalytic efficiency under sunlight, including chemical doping, mechanical strain and formation of heterojunction structures. Nevertheless, the progress of current research in photocatalysis for water splitting reaction is still very slow, and many fundamental details and underlying mechanisms remain unraveled. In this study, we employed first-principles density functional theory calculations to investigate the electronic property changes of the strained anatase TiO2 as well as the band lineup at the rutile-anatase interface. There are two main focuses in this thesis: In the first part of the thesis, we investigated the effect of mechanical strains on the electronic property changes of anatase TiO2, which include the variations of electronic bang gaps, energy levels of VBM and CBM, and the effective masses of charge carriers. In our strained models, biaxial and uniaxial strains were imposed along the directions parallel to the (101), (100), and (001) surfaces, respectively, to mimic the lattice deformations arising from the lattice mismatch with the underlying substrates. Our calculated results show that the band gap of anatase TiO2 can be effectively reduced when [1 ¯01] uniaxial compressive strain is in the (101) surface, [001] uniaxial compressive strain is in the (100) surface, and [100]&;[010] biaxial tensile strains is in the (001) surface, respectively. Our calculations also show that it is possible to make the energy level of CBM go upward while the band gap is reduced in the meanwhile when the (001) surface is under biaxial tensile stress. Furthermore, for all the strained structures that can cause band gap reduction, the variations of the effective masses for electrons and holes do not show negative impact on charge carrier separation. These results indicate that the photocatalytic activity of anatase TiO2 can be fine-tuned by applying mechanical strain along certain direction on this material system. In the second part of the thesis, we studied the intrinsic band alignment at the rutile-anatase interface to understand the origins of the synergistic effect observed in the mixed phase TiO2 system. This synergic effect to enhance the separation of photo-excited charge carrier is generally believed to be attributed to a staggered band offset between the two phases. Nevertheless, the explicit direction of charge flow remains controversial and is still under intensive debate. To clarify this controversy, we have constructed two interface models, anatase(112)/rutile(100) and anatase(110)/rutile(011), respectively, to calculate their band alignments using first-principles density functional theory calculations. Our calculated results show that there is indeed a staggered band lineup at the rutile/anatase interface and both VBM and CBM of rutile lie higher in energy than those of anatase phase. The offset values of VBM/CBM were found to be 0.468 ±0.12eV/0.268 ±0.12eV for rutile(100)/anatase(112) interface, and 0.467±0.07eV/0.267±0.07eV for rutile(011)/ anatase(110) interface, respectively. Based on this result, the photo-excited electrons would majorly transport from rutile to anatase while the hole would favor in the opposite direction, which can help enhance the charge carrier separation resulting in better photocatalytic activity of the mixed phase TiO2. On the other hand, we also employed the vacuum level alignment method to study the band lineup at the rutile/anatase interface without acquiring detailed knowledge of the interface structures. Basically, the band alignments obtained using this method are consistent with those predicted based on the realistic interface structure models, providing a convenient way to acquire the preliminary guess for the band lineup of the heterojunction material systems.
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Shih, Min-Chuan, and 施敏權. "Atomic-scale observation of the interfacial band alignment and photogenerated carrier distribution in polymer-based and perovskite-based solar cells." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/57744546569517670675.
Full textAbstract:
博士國立中山大學
物理學系研究所
104
Heterointerface properties represent a critical point to achieve high power conversion efficiency in solar cells. The ongoing improvement can be advanced when deep understanding of the nanomorphological distribution and the corresponding electronic structure can be determined. Therefore, the understanding of interfacial electronic properties inside the photoactive layer will be of crucial importance to further enhance the charge generation, transport, and collection, and the corresponding device performances and stabilities of polymer-based and perovskite-based solar cells. In the first part, we demonstrate cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S) measurements to direct visualize the atomic-scale interfacial band alignment across the film thickness in the model system of polymer-based solar cells, i.e. phase segregated blends of poly(3-hexylthiophene) (P3HT)/ [6,6]-phenyl C61 butyric acid methyl ester (PCBM). We were able to achieve the direct observation of the interfacial band mappings at the donor (P3HT)/acceptor (PCBM) interface and at the interface between the photoactive layer and the anode modification layer with an atomic-scale resolution. The second part, the light-modulated scanning tunneling microscopy (LM-STM) was utilized to reveal the correlation of the nanoscaled compositional distributions and interfacial electronic structures at grain boundaries of polycrystalline CH3NH3PbI3 perovskite grains under light illumination, which enables us to directly obtain the mapping images of photogenerated carriers of electrons and holes and the photoinduced interfacial band bending of both the valence band and conduction band for the first time. The unique advantages of using XSTM to investigate polymer/fullerene bulk heterojunction solar cells allow us to observe simultaneously the quantitative link between the vertical morphologies and the corresponding local electronic structures. Furthermore, the LM-STM is utilized to explore the real-space observation of photoinduced carrier generation and interfacial band bending at grain boundaries of perovskite crystals under light illumination. The direct observation of the interfacial band alignment inside the photoactive layer infers that the photogenerated carriers’ behavior, which is crucial for improving the efficiencies of the charge separation, collection and transportation for polymer-based and perovskite-based solar cells.
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"Electronic States of High-k Oxides in Gate Stack Structures." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.15179.
Full textAbstract:
abstract: In this dissertation, in-situ X-ray and ultraviolet photoemission spectroscopy have been employed to study the interface chemistry and electronic structure of potential high-k gate stack materials. In these gate stack materials, HfO2 and La2O3 are selected as high-k dielectrics, VO2 and ZnO serve as potential channel layer materials. The gate stack structures have been prepared using a reactive electron beam system and a plasma enhanced atomic layer deposition system. Three interrelated issues represent the central themes of the research: 1) the interface band alignment, 2) candidate high-k materials, and 3) band bending, internal electric fields, and charge transfer. 1) The most highlighted issue is the band alignment of specific high-k structures. Band alignment relationships were deduced by analysis of XPS and UPS spectra for three different structures: a) HfO2/VO2/SiO2/Si, b) HfO2-La2O3/ZnO/SiO2/Si, and c) HfO2/VO2/ HfO2/SiO2/Si. The valence band offset of HfO2/VO2, ZnO/SiO2 and HfO2/SiO2 are determined to be 3.4 ± 0.1, 1.5 ± 0.1, and 0.7 ± 0.1 eV. The valence band offset between HfO2-La2O3 and ZnO was almost negligible. Two band alignment models, the electron affinity model and the charge neutrality level model, are discussed. The results show the charge neutrality model is preferred to describe these structures. 2) High-k candidate materials were studied through comparison of pure Hf oxide, pure La oxide, and alloyed Hf-La oxide films. An issue with the application of pure HfO2 is crystallization which may increase the leakage current in gate stack structures. An issue with the application of pure La2O3 is the presence of carbon contamination in the film. Our study shows that the alloyed Hf-La oxide films exhibit an amorphous structure along with reduced carbon contamination. 3) Band bending and internal electric fields in the gate stack structure were observed by XPS and UPS and indicate the charge transfer during the growth and process. The oxygen plasma may induce excess oxygen species with negative charges, which could be removed by He plasma treatment. The final HfO2 capping layer deposition may reduce the internal potential inside the structures. The band structure was approaching to a flat band condition.Dissertation/Thesis
Ph.D. Physics 2012