Dissertations / Theses on the topic 'OPTOELECTRONICS APPLICATIONS'
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Lee, Tae-Hee. "Silver nanocluster single molecule optoelectronics and its applications." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-01302004-144007/unrestricted/lee%5Ftaehee%5F200405%5Fphd.pdf.
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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2004.Srinivasarao, Mohan, Committee Member; Sherrill, C. David, Committee Member; Orlando, Thomas, Committee Member; EL-Sayed, Mostafa, Committee Member; Dickson, Robert, Committee Chair. Vita. Includes bibliographical references (leaves 136-159).
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Annetts, Paul Julian. "Advanced applications of semiconductor optical amplifiers." Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299275.
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Lansley, Stuart Peter. "Diamond photodetectors for deep ultra-violet applications." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269925.
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Occhi, Luca. "PEDOT:PSS-based hybrid materials for optoelectronics applications." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/61335.
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Organic electronics is a research area that, in recent year, has received increasing attention both from academia and industry. Performance of organic optoelectronic devices, such as organic light-emitting diodes (OLEDs) and organic photovoltaic devices (OPVs), relies on the electrical and optical characteristics of each component. However, the performance are frequently limited by the distribution of the internal electromagnetic field: an effective light management, involving either the incoupling of incident radiation (in case of photovoltaic cells and photo-detectors), or the outcoupling of emitted light (for light-emitting diodes), is crucial. The electric field distribution may be optimised by adjusting the device geometry or, alternatively, by modifying the optical properties (i.e. refractive index and absorption coefficient) of each component. Developing a material with tunable optical properties, whilst maintaining acceptable electrical characteristics, would offer a significant alternative in high-performance devices. Among the different compounds used in organic devices, the charge injection/extraction materials play a key role: the ubiquitous poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is an example of an organic compound often limited (in thickness) by the optical losses. In this work we introduce an innovative, solution-processable, inorganic/organic hybrid material based on PEDOT:PSS, which could be used as an efficient hole-transport layer, or as an electrode, in OLEDs and OPVs. The hybrid system exhibits high optical quality, a dramatic increase of refractive index (up to +12-13%), and a decrease in work function, whilst maintaining good electrical conductivity. We prove the effectiveness of our approach both by modeling the distribution of normalised modulus squared of the optical electric field in light-emitting structures. Furthermore, we fabricate and characterise optoelectronic devices (OLEDs and OPVs) with PEDOT:PSS hybrid hole-transport layers, demonstrating an increase of efficiency in the organic light-emitting diodes. Finally, we investigate the thermoelectric properties of hybrid material, thus opening interesting new applications for our hybrid compound.
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Asil, Demet. "Hybrid functional semiconductors for optoelectronic applications." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708582.
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Moreira, Paulo Manuel Rodrigues Simões. "Optical receiver design and optimisation for multi-gigahertz applications." Thesis, Bangor University, 1993. https://research.bangor.ac.uk/portal/en/theses/optical-receiver-design-and-optimisation-for-multigigahertz-applications(851ce42c-3b48-488f-88c3-8f4137b79607).html.
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This thesis is concerned with structures and design techniques appropriate for the realisation of integrated optical receivers operating at multi-gigahertz frequencies. The development and practical proving of novel signal designs tailored specifically to very high bit-rate optical communication systems is reported. Timing imperfections and signal dependent noise - a result of the optical amplification deployed in all high-performance systems - are two major impairments that must be accommodated if optimum system performance is to be achieved. Here, a signal design that accommodates these impairments is developed and compared to established designs. The new signal designs are shown to provide improved performance, in particular, they exhibit tolerance to uncertainty in the exact level of the impairment. Following the derivation of the signal designs a range of practical realisations are described. A receiver amplifier GaAs MMIC for 4.8 Gbit/s operation with embedded signal shaping is described followed by the design and test of integrated post-detection filters for 10 and 15 Gbit/s systems. The susceptibility of the embedded signal shaping receiver to variations in photodiode capacitance leads to the development and test of a low inputimpedance common-gate 5 Gbit/s GaAs MMIC receiver. To effect signal shaping at very high data-rates a modified distributed amplifier structure is proposed which better utilises the capabilities of the available foundry processes. Two distributed amplifier based optical receivers with embedded signal shaping are devised and simulation results for 10 Gbit/s show the efficacy of this design approach. The implications of noise matching are investigated and a 2 GHz SCM receiver is used as a vehicle to illustrate the methods developed. The long term goal of receiver design is to fully integrate bnth optical and electrical components onto a single chip. A preliminary investigation of the feasibility of this goal is carried out on an experimental InP-based process. Two receiver designs for 10 Gbit/s were prepared as a precursor to a detailed design of an OEIC with embedded signal shaping that incorporates the novel topologies developed during this work.
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Gebremichael, Yonas Meressi. "Highly birefringent fibre based polarisation modulated ellipsometry and sensor applications." Thesis, City University London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390940.
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Addington, J. Shawn. "Integrated optoelectronics applications in fiber optic receiver packaging." Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/37463.
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The objective of this research is the' development and evaluation of a new style of integrated optoelectronics. The approach combines the selectivity of traditional hybrid integration with the "internal" interconnection capabilities of monolithic integration, through the use of low temperature cofireable ceramic (LTCC) tape systems. This new integration technique is applied to a fiber optic receiver system, and focuses on three main tasks. The first task involves the realization, and eventual hybridization, of the receiver electronics, including the photodetector and the associated amplifier circuitry. Second, materials and techniques for the processing of planar optical waveguides are investigated, in order to expand the potential applications of the technique. Finally, a new technique of integrating an optical fiber with the above components is introduced and evaluated.
Multichip module (MCM) technology has become the new standard in the field of electronic packaging. Much of the success of MCM packaging may be attributed to the development of LTCC systems. LTCC materials utilize their multilayer (3-dimensional) nature to achieve a higher level of electronic circuit density within a hermetic module. The goal of this research effort is to expand this capability to include optical components, in addition to the traditional electronics. The optical counterpart to the printed electrical wiring within an LTCC package is the planar waveguide. Much of this research is therefore devoted to an investigation of materials and processing techniques used to develop planar optical waveguide structures. This research discusses the production and evaluation of both thin film and thick film structures based on germanium oxide (GeO₂) - a material with promising photosensitivity characteristics. As has been seen with optical fibers, the optimization of planar optical waveguides is also not a trivial task. Aside from the material and processing concerns, there is also the compatibility with cofireable ceramic materials that must be addressed.
Once these planar optical waveguides are able to be incorporated within the internal layers of the multichip module, there must be a means of accessing them from the outside of the package. Thus this research work also investigates the ability to integrate optical fibers within LTCC materials. Traditional optical fiber connectors are not suitable for this application, since the interface between fiber and waveguide will be inside a hermetic module. This research discusses the techniques used to· achieve this novel integration capability. The planar optical waveguides developed in this work are not yet optimized for full integration within cofireable ceramic materials. Thus, the interface between fiber and waveguide is theoretically. analyzed from the perspective of coupling efficiency. Nevertheless, the ability to integrate an optical fiber within an LTCC module is demonstrated through the development of a fiber optic receiver module. One of the benefits of the integration technique proposed in this research work is selectivity. This feature is demonstrated through the evaluation and selection of individual components of the receiver system. This work demonstrates that the selection of receiver components is not dictated by the integration technology, but is determined instead by individual performance characteristics.
Through the hybridization of the receiver circuitry and the successful integration of an optical fiber within the LTCC material, a functional integrated fiber optic receiver module has been completed. In addition, this research into the development of both thick and thin film planar optical waveguide materials is an important step toward the eventual integration of these devices.Ph. D.
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Pratt, Andrew Richard. "Control of indium migration on patterned substrates for optoelectronic device applications." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307775.
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Moon, Kevin. "Design and characterisation of CCD detector systems for x-ray applications." Thesis, University of York, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311014.
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Sambasivan, Nadarajah. "The adhesion of an optical adhesive to glass substrates for optoelectronics applications." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/843340/.
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Surface characterisation and failure mechanisms of adhesively bonded glass butt joints were studied. Materials of relevance to the adhesive bonding of fibre optic components were employed: a fine annealed Grade A glass (Schott(TM) BK - 7), and a fast curing epoxy based optical adhesive. The joint behaviour and their durability under adverse environmental conditions were investigated, and the subsequent, failed joint fracture surfaces were examined using XPS, ToF-SIMS and SEM. Surface analysis techniques have been employed to characterise components of the adhesive systems and to interrogate the surface of failed joints with a view to establishing the locus of failure. Joints were immersed in pure water for period of 0 - 270 days at 35°C. Substantial reduction in the bond strength within a few days of water immersion was observed. Also for the joints left in for a prolonged exposure periods (> 100 days) the strength values reached a minimum value. The surface analysis of the joints has indicated a cochoidal brittle fracture through the adhesive in dry conditions, and an interfacial failure for wet joint fractures. Calculations of the polymer thickness on the interfacial surfaces indicated a decrease in overlayer thickness. This reduction reached a constant value for joints left in water for more than 100 days. During this investigation surfaces segregation of minor components of the adhesive such as amine and diluent was also identified by ToF-SIMS and XPS. In order to study this phenomenon further, reformulation of the adhesive has been carried out. Six adhesives were formulated, of which three resins were based on the change in diluent content of the system, three were based on the change in amine concentrations. This work has clearly identified amine segregation only at the interfacially failed joints. It is expected that when the joints cures very fast, even if the formulation contains very high proportion of amine, the segregation is minimal. Also, some evidence of diluent migration at the interfaces was observed during the reformulation studies.
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Hughes, Patrick Joseph. "Photoreflectance characterisation of AlGaAs/GaAs single quantum well structures for optoelectronic applications." Thesis, University of Surrey, 1995. http://epubs.surrey.ac.uk/844385/.
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The modification of the optical properties of quantum well structures by post growth thermal diffusion techniques is important for the fabrication and integration of quantum well devices for optoelectronic applications. This thesis is concerned with the characterisation of as-grown and thermally interdiffused quantum well structures using room temperature photoreflectance. In particular, all the interband transitions (symmetry 'allowed' and 'forbidden') in the subband of four AlGaAs/GaAs single quantum well structures were determined using photoreflectance. The identification of the transitions was complicated by the presence of Franz-Keldysh oscillations in all photoreflectance spectra which were associated with an interface built-in electric field in the as-grown structures. The source and magnitude of the field on either side of the interface was determined after the sequential etching and photoreflectance analysis of these structures. From the spectra of the etched structures, optical interference effects were found which enabled the layer thicknesses in these structures to be determined. High temperature rapid thermal annealing of these structures resulted in interdiffusion across the well barrier interfaces of the quantum well structures which modified the subband structure, and therefore the optical properties, of the quantum well. This annealing was found to produce limited interdiffusion by correlating the relative 'blue shifts' of the interband transitions with those of a theoretical model. Good agreement with the model was obtained, which allowed temperature dependent interdiffusion co-efficients and an activation energy to be determined. The effects of oxygen ion implantation followed by annealing was also studied and found to significantly enhance the extent of the interdiffusion. In addition, interband transitions of heavy-hole and light-hole character were distinguished from polarisation studies while temporal studies resulted in the identification of unintentional impurities and the determination of photocarrier trap times in the as-grown and implanted structures. The work presented here demonstrates the versatility of photoreflectance for the room temperature characterisation of as-grown and thermally processed quantum well structures for optoelectronic devices, prior to fabrication.
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Duffy, Christopher. "Stimulated Brillouin Scattering In Monomode Optical Fibres For Sensing And Signal Processing Applications." Thesis, Cranfield University, 1994. http://dspace.lib.cranfield.ac.uk/handle/1826/4550.
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This thesis describes research into non-linear optical effects in monomode
fibres for sensing and signal processing schemes. The work is initially placed
into the context of relevant fibre sensor applications for aerospace. Candidate
non-linear processes are then described and Stimulated Brillouin Scattering
(SBS) targeted as a suitable mechanism. The SBS process in monomode
fibres is then fully described, including a theoretical assessment of the magnitude
of both pump and Stokes signals with fibre length.
The project developed, firstly, an all-optical frequency shifter using SBS
which generated output carriers in the 1-70OMHz regýon, depending on fibre
type and system topology. In particular, a single-fibre system was demonstrated
for the first time. Limitations of the technique arose through fibre
photosensitivity and non-linear dynamical effects which, respectively, increased
the input pump power requirements and introduced intensity and
frequency instabilities into the output signal. Both processes were investigated
fully. Optical fibre and pump characteristics, and system configurations,
were therefore identified which minimised their impact.
The same SBS heterodyning principles were then used to investigate
single-pump sensor systems. Both 'quasi-point' and two-element, multiplexed
temperature sensors were demonstrated. A linear relationship between
the Stokes frequency and temperature was obtained from 5 to 55'C,
determined primarily by the thermal response of the acoustic phonon velocity.
The sensing resolution was typically ±2'C, limited by the non-linear dynamical
effects, and the spatial resolution was determined by the pump/fibre
interaction length. One unique sensing element per optical input was demonstrated.
These results are then placed in the context of systems utilising
alternative SBS-based strategies, other non-linear effects and fibre ring resonators.
Management elements of the project were covered by detailing both the
technical and strategic motivations for undertaking the research and, by describing
the issues on which a cost benefit analysis of fibre sensors for aircraft
can be undertaken.
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Yu, S. F. "Investigation of grating coupled surface emitting lasers for optical interconnects and signal processing applications." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319578.
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Saberi, Moghaddam Reza. "Metal oxide nanostructures for hybrid optoelectronic applications." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709034.
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Harwell, Jonathon R. "Optoelectronic applications of lead halide perovskites." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16943.
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Hybrid perovskites are a new class of semiconductor which have proven to be an ideal material for making thin film solar cells. They have the advantages of flexibility, low cost, and easy processing, whilst achieving efficiencies competitive with monocrystalline silicon. Many of the properties which make them ideal for solar cells are also applicable to light emitting devices, and there is now increasing interest in their application for light emitting diodes (LEDs) and lasers. This thesis aims to use a range of novel spectroscopy techniques to investigate the origin of these favourable properties, and to exploit these properties to produce high performance distributed feedback lasers. A detailed understanding of the origins of the excellent properties of hybrid perovskites is of crucial importance in the search for new variations with improved performance or lowered toxicity. This thesis uses Kelvin probe, air photoemission, and resonant ultrasound spectroscopy to probe deeply into the underlying physics of hybrid perovskite single crystals and devices. Using these techniques, we are able to produce detailed maps of the energy levels in a common perovskite solar cell, and we also gain strong insight into the underlying strains and instabilities in the perovskite structure that give rise to their elastic properties. The strong light emission of hybrid perovskites is then exploited to produce high quality distributed feedback lasers emitting in the green and infrared part of the spectrum. These lasers are observed to have superior stability, good thresholds, and many interesting beam parameters owing to their high refractive index. We explore a wide range of processing methods in order to achieve the lowest lasing threshold and the best stability. Finally, we investigate the properties of low dimensional perovskites and investigate their potential in optoelectronic applications.
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Charati, Manoj B. "Peptides and polypeptides as scaffolds for optoelectronics and biomaterials applications." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 200 p, 2009. http://proquest.umi.com/pqdweb?did=1891590581&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Wen, Xiaonan. "Piezotronics as an electromechanical interfacing technology for electronic and optoelectronic applications." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53844.
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Innovation on human-machine interfacing technologies is critical for the development of smart, multifunctional and efficient electronic/optoelectronic systems. The effect of piezotronics is a newly started field of study, which utilizes piezoelectric polarization that is mechanically induced inside a piezoelectric semiconductor to regulate electron transport across electronic contact interfaces. With the concept coined in 2006, many efforts have been contributed to studying the underlying physical mechanism of this effect as well as demonstrating various applications based on single nanowire piezotronic devices. This thesis selects ZnO as the material foundation and was started by firstly studying flexible, controllable and scalable synthesis methods for ZnO nanowires array and thin film. By replacing the use of random, individual nanowires with these materials, novel piezotronic and piezophototronic devices were designed, fabricated and tested to achieve the function of strain sensing, tactile imaging, piezo-enhanced photodetection and solar energy harvesting. The adoption of nanowires array and thin film materials over single nanowires leads to significant advantages in terms of scalable fabrication, industrial compatibility and broader functionality. By consistently going down this route, we believe that the field of piezotronics will eventually make revolutionary impact on MEMS, optoelectronics, multifunctional sensor networks, human-machine interfacing and so on.
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Hallani, Rawad Kamal. "Designing Anthradithiophene Derivatives Suitable For Applications in Organic Electronics and Optoelectronics." UKnowledge, 2015. http://uknowledge.uky.edu/chemistry_etds/61.
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Anthradithiophene (ADT) derivatives have proven to be a front-runner in the world of small molecule semiconductors for organic electronics and optoelectronics. This is mainly due to the improved stability, easy tuning of chemical and physical properties, and impressive device performance that these molecules possess, especially in organic field effect transistors (OFET) and organic photovoltaics (OPV). The second chapter of this dissertation shows that reducing the amount of alkylsilylethynyl groups, used for functionalizing and solubilizing the ADT backbone, does alter the chemical, physical and crystallographic properties of ADTs. These changes offer the opportunity to study and observe different intermolecular interactions as well as monitoring their influence on sulfur scrambling in solid state. Additionally, from the early days ADTs and functionalized ADTs have been synthesized as isomeric mixtures. In chapter three, I demonstrate a new and simple method that can separate the syn and anti isomers of the F-TES-ADT and F-TEG-ADT chromatographically. The effects of isomeric purity on crystal packing and field effect transistor performance were studied extensively.
Chapter four of this dissertation reveals a new generation of acceptor (electron poor) ADT derivatives obtained by attaching cyanide as electron withdrawing group (EWG) to the ADT chromophore. An extensive study was conducted on CN-ADT (acceptor) molecules in small molecule (F-TES-ADT) donor/ small molecule (CN-ADT) acceptor binary BHJ blends as well as P3HT/CN-ADT/PCBM ternary BHJ blends. Photophysical studies of the Donor/ acceptor blends (interface, domains, and crystal orientation) were conducted to obtain a better understanding of the film morphology and its effect on solar cell performance.
Finally, the last part of the dissertation, Chapter five, focus on studying singlet fission in ADT derivatives, as well as the effect of varying the size of the alkylsilylethynyl functional group (used for solubilizing the ADT backbone) on altering the electronic couplings and how can that potentially affect the singlet fission rate in these molecules. We also tried to inspect the extent of the correlation between long-range order in crystal packing and singlet fission by monitoring singlet fission rate and efficiency for ADT derivatives with different thin film morphologies.
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Elsayed, Moussa Mehdi. "Supramolecular assemblies with organophosphorated based derivatives for potential applications in optoelectronics." Thesis, Rennes 1, 2013. http://www.theses.fr/2013REN1S135.
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Au cours de ce travail, nous avons préparé des clips moléculaires efficaces à partir de dimères de cuivre(I) ou d'or(I) portant des ligands organophosphorés en tirant parti des interactions métallophiles. Dans un premier temps, un complexe de cuivre(I) portant des ligands bis(2-pyridyl)phospholes a été utilisé comme clip moléculaire pour organiser des systèmes pi monotopiques à fonction cyano et portant divers fragments pi-conjugués. Ces dimères formés par assemblage pis'auto-organisent à l'état solide en colonnes pi infinies. Dans un deuxième temps, un complexe d'or(I) portant un ligand biphosphole a été utilisé comme clip moléculaire pour organiser des unités éthynyl[6]helicenes en dimères. Ces dimères ont montré une augmentation des propriétés chiroptiques par rapport au ligand éthynyl[6]helicene libre. Dans un troisième temps, un complexe bimétallique de cuivre(I) portant des ligands 1,1-bis(diphénylphosphino)méthane (dppm) s'est révélé être un clip moléculaire efficace pour la conception d'architectures supramoléculaires auto-assemblées par réaction avec des cyanométallates. Ces dérivés supramoléculaires ont des topologies différentes et sont émissifs dans le domaine visible après excitation dans l'UV. Dans certains cas, ils ont montré des propriétés de luminescence thermochromique intéressantesIn this work, we have prepared organophosphorated ligands based copper(I) or gold(I) dimers that act as efficient molecular clips thanks to metallophilic interactions. Firstly, a bimetallic copper(I) complex bearing bis(2-pyridyl)phosphole ligands was used as a molecular clip to organize monotopic cyano-capped pi-systems carrying various pi-conjugated fragments into self-assembled pi-stacked dimers. These dimers organized in the solid state within infinite columnar pi-stacks. Secondly, a bimetallic gold(I) complex bearing a biphosphole ligand was used as a molecular clip to organize ethynyl-capped [6]helicene moieties into self-assembled dimers. These dimers showed an enhancement of the chiroptical properties as compared to the free ethynyl[6]helicene ligand. Thirdly, a bimetallic copper(I) complex bearing 1,1-bis(diphenylphosphino)methane (dppm) ligands has revealed a powerful molecular clip to design self-assembled supramolecular architectures by reaction with different cyanometallates. These supramolecular derivatives have different topologies and are emissive in the visible spectrum upon UV excitation and in some cases they showed intriguing thermochromic luminescence properties
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Augustine, Godfrey. "Modeling, fabrication, and characterization of InP thin films and dvices for optoelectronic applications." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/15382.
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Goedel, Karl Christoph. "Optoelectronic applications of solution-processable sulfide semiconductors." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/268085.
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Solar cells and photodetectors rely on similar physical principles based on the interaction of light and matter. Both types of optoelectronic devices are indispensable in a wide range of technological applications, from large-scale renewable power conversion to everyday consumer items. In this thesis, the use of facile solution-processable semiconductors in solar cells and light sensors is studied with a focus on antimony sulfide (Sb₂S₃) and antimony sulfoiodide (SbSI). The improvement of the photovoltaic performance in Sb₂S₃ sensitized solar cells upon the controlled partial oxidation of the absorber layer is investigated. A reduction in charge carrier recombination is the reason for the improved efficiency, caused by the oxidation process. Further, a new chemical bath deposition method for antimony sulfide is developed. Carried out at room temperature, this technique eliminates the necessity of cooling equipment during the deposition process. The antimony sulfide from this method decreases the density of trap states compared to the conventional deposition. Power-conversion efficiencies of up to η=5.1% are achieved in antimony sulfide sensitised solar cells using the new room temperature deposition method. Finally, antimony sulfide is used as a precursor to form films of antimony sulfoiodide (SbSI) micro-crystals in a facile physical vapour process. These films are then used to fabricate photodetectors. With PMMA as an insulating spacer layer, the devices are built in a sandwich-type architecture. Optoelectronic characterisation shows that these devices have the shortest response and recovery times reported for SbSI photodetectors to date.
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Jones, Gareth Francis. "Modification of graphene for applications in optoelectronic devices." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/31537.
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In this thesis, we investigate how the optical and electronic properties of graphene may be modified in proximity to various other materials. We present several examples of how modification in this way can help make graphene better suited for specific device applications. We develop a method of up-scaling the fabrication of FeCl3-intercalated few-layer graphene from micron-sized flakes to macroscopic films so that it may be used as a transparent electrode in flexible light-emitting devices. We also find that photo-responsive junctions can be arbitrarily written into FeCl3-intercalated few-layer graphene by means of optical lithography. These junctions produce photocurrent signals that are directly proportional to incident optical power over an extended range compared to other graphene photodetectors. Through theoretical analysis of these junctions, we conclude that the enhanced cooling of hot carriers with lattice phonons is responsible for this behaviour. Finally, we trial rubrene single crystals as the light-absorbing layer in a graphene phototransistor. We find that rubrene single crystal-graphene interfaces exhibit enhanced charge transfer efficiencies under illumination with extremely weak light signals. Through a comparative study with similar devices, we conclude that the wide variation in sensitivity amongst graphene phototransistors is largely due to extraneous factors relating to device geometry and measurement conditions.
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Cheng, An-jen Park Minseo Tzeng Y. "One dimensional zinc oxide nanostructures for optoelectronics applications solar cells and photodiodes /." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SUMMER/Electrical_and_Computer_Engineering/Dissertation/Cheng_An-jen_33.pdf.
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Stamplecoskie, Kevin. "Silver Nanoparticle Controlled Synthesis and Implications in Spectroscopy, Biomedical and Optoelectronics Applications." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24164.
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This thesis describes the photochemical synthesis of silver nano particles, several ways to make these particles as well as control the size and shape of the colloidal particles. Understanding the primary reactions in photochemical nanoparticle formation has lead to important contributions to the overall mechanism of metal nanoparticle synthesis. The size and shape control of the particles is shown to have important implications for the Raman spectrum of surface bound molecules. The particles have also been used in antibacterial properties where it was shown that silver nanoparticles are more antibacterial than the corresponding silver cation, while remaining non-toxic to several common cell lines. The particles were also shown to have some interesting properties that can be exploited in lithography and optoelectronics.
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Hamada, Tomoyuki. "Ab Initio Molecular Orbital Study of Nonlinear Optical Materials for Optoelectronics Applications." Kyoto University, 1998. http://hdl.handle.net/2433/182321.
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Kahn, Mohammed Tariq Ekeramodien. "Development of a non-monochromatic lightwave sensor for applications in smart structures research." Thesis, Peninsula Technikon, 1998. http://hdl.handle.net/20.500.11838/888.
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Thesis (MTech (Electrical Engineering))--Peninsula Technikon, Cape Town, 1998The purpose of this study was to perform an investigation into advances in the field of opto-electronics and to develop a suitable lightwave sensor, for application in smart structures research. Included in the scope of this research was the theoretical development and analysis of an appropriate technology to lead to an implementation of such sensors. This project forms part of an overall plan to gain experience in optoelectronic (photonic) sensor design. In research done previously in smart structure monitoring, piezo-electric techniques with the usual electrical interconnections was used. In a highly distributed sensor system the problems of electromagnetic interference, the tribo-electric effect and noise could be problematic. In this research, opto electronic techniques were thoroughly researched and an improvement on laser based fibre-optic interferometers was made. A non monochromatic lightwave interferometer was developed from theory and a prototype tested. The results suggests that an interferometric sensor can be operated with a non monochromatic source by using a second interferometer to modulate the frequency spectrum of the light before it is detected by a photodetector. Various test and measurement circuits for improved photodetector performance were evaluated, as well as a study of signal processing techniques that would be of use for an upgrade of the project where specific feature detection and analysis using the sensor is envisaged. A specification for a computer based data acquisition system was developed to do initial tests. The project should continue, with the sensor head being improved and all the necessary signal processing routines programmed into a Labview based data acquisition system.
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Zaman, Saima. "Synthesis of ZnO, CuO and their Composite Nanostructures for Optoelectronics, Sensing and Catalytic Applications." Doctoral thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-81120.
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Research on nanomaterials has become increasingly popular because of their unique physical, chemical, optical and catalytic properties compared to their bulk counterparts. Therefore, many efforts have been made to synthesize multidimensional nanostructures for new and efficient nanodevices. Among those materials, zinc oxide (ZnO), has gained substantial attention owing to many outstanding properties. ZnO besides its wide bandgap of 3.34 eV exhibits a relatively large exciton binding energy (60 meV) at room temperature which is attractive for optoelectronic applications. Likewise, cupric oxide (CuO), having a narrow band gap of 1.2 eV and a variety of chemo-physical properties that are attractive in many fields. Moreover, composite nanostructures of these two oxides (CuO/ZnO) may pave the way for various new applications. This thesis can be divided into three parts concerning the synthesis, characterization and applications of ZnO, CuO and their composite nanostructures. In the first part the synthesis, characterization and the fabrication of ZnO nanorods based hybrid light emitting diodes (LEDs) are discussed. The low temperature chemical growth method was used to synthesize ZnO nanorods on different substrates, specifically on flexible non-crystalline substrates. Hybrid LEDs based on ZnO nanorods combined with p-type polymers were fabricated at low temperature to examine the advantage of both materials. A single and blended light emissive polymers layer was studied for controlling the quality of the emitted white light. The second part deals with the synthesis of CuO nanostructures (NSs) which were then used to fabricate pH sensors and exploit these NSs as a catalyst for degradation of organic dyes. The fabricated pH sensor exhibited a linear response and good potential stability. Furthermore, the catalytic properties of petals and flowers like CuO NSs in the degradation of organic dyes were studied. The results showed that the catalytic reactivity of the CuO is strongly depending on its shape. In the third part, an attempt to combine the advantages of both ZnO and CuO NSs was performed by developing a two-step chemical growth method to synthesize the composite NSs. The synthesized CuO/ZnO composite NSs revealed an extended light absorption and enhanced defect related visible emission.
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Narayan, R. "Development of novel methacrylic and supramolecular comb polymers of rylenebisimides for applications in optoelectronics." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2013. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2186.
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Lee, Kyoung-Keun. "Implementation of AlGaN/GaN based high electron mobility transistor on ferroelectric materials for multifunctional optoelectronic-acoustic-electronic applications." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28209.
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Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.Committee Chair: William. Alan Doolittle; Committee Member: Jeffrey Nause; Committee Member: Linda S. Milor; Committee Member: Shyh-Chiang Shen; Committee Member: Stephen E. Ralph.
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Hosatte, Mikaël. "Nanostructured silicon-based metamaterial and its process of fabrication for applications in optoelectronics and energy." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAD019.
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Des nanostructures basées sur des différences de cristallinité ont été insérées dans des cellules test en silicium par des techniques d’amorphisation innovantes. Un nouveau mécanisme de multiplication de porteurs a ainsi été observé. Cet effet peut provenir des niveaux d’énergie électronique introduits par de grandes densités locales de bi-lacunes. Un principe de fonctionnement impliquant des mécanismes à niveaux d’énergie multiples et un transport électronique rapide au sein de la bande d’énergie des atomes de phosphore non-ionisés a également été proposé. Cela conduit à une asymétrie favorable entre la génération et la recombinaison des porteurs libres.L’énergie nécessaire à un photon pour enclencher le procédé s’est révélée plus petite que deux fois celle de la bande interdite. L’amélioration du rendement photovoltaïque devient donc concevable et une nouvelle génération de cellules solaires à haute efficacité pourrait ainsi émerger de cet effet de multiplication à faible-énergieNanostructures based on differences of crystallinity have been embedded into all-silicon test devices by innovative amorphization techniques and a new carrier multiplication mechanism was observed. This effect can indeed originate from the electron energy levels resulting from the high densities of divacancies localized at the crystalline/amorphous interfaces.An operating principle involving multiple energy level mechanisms and fast electronic transport within the unionized phosphorus energy band was also advanced. It led to a favourable asymmetry between generation and recombination of free carriers.Besides, contrary to other carrier multiplication effects, photon energy lower than twice the band gap was found sufficient to initiate the process. The enhancement of photovoltaic yields becomes therefore conceivable and propositions of prototypes are made. A new generation of high efficiency solar cells may then emerge from this Low-Energy Electron Multiplication effect
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Giri, Binod. "Controlled Synthesis of Nanostructured Two-dimensional Tin Disulfide and its Applications in Catalysis and Optoelectronics." Digital WPI, 2020. https://digitalcommons.wpi.edu/etd-dissertations/609.
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Tin disulfide (SnS2) is a two-dimensional (2D) material with excellent properties and high prospects for low-cost solutions to catalytic and optoelectronic applications. In this work, vertical nanoflakes of SnS2 have been synthesized using custom-designed close space sublimation (CSS) system and investigated for applications in photoelectrochemical (PEC) water oxidation and metal-semiconductor-metal (MSM) photodetector. For the PEC application, vertical SnS2 nanoflakes grown directly on transparent conductive substrates have been used as photoanodes, which produce record photocurrents of 4.5 mA cm−2 for oxidation of a sulfite hole scavenger and 2.6 mA cm−2 for water oxidation without any hole scavenger, both at 1.23 VRHE in neutral electrolyte under simulated AM1.5G sunlight, and stable photocurrents for iodide oxidation in acidic electrolyte. This remarkable performance has been attributed to three main reasons: (1) high intrinsic carrier mobility of 330 cm2 V−1 s−1 and long photoexcited carrier lifetime of 1.3 ns in the nanoflakes, (2) the nanoflake height that balances the competing requirements of light absorption and charge transport, and (3) the unique stepped morphology of these nanoflakes that improves photocurrent by exposing multiple edge sites in every nanoflake. In another application, these SnS2 nanoflakes have been used to enhance the performance of lead sulfide quantum dot (PbS QDs) photodetectors by providing a high-mobility channel for photoexcited charges from PbS QDs, which results in 2 orders of magnitude enhancement in responsivity. The physical models and experimental findings presented in this dissertation can help engineer more cost-effective solutions for PEC water splitting and optoelectronics based on 2D metal dichalcogenides.
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Gibbons, Michael J. "Robust, reusable qubits for quantum information applications." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39474.
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Most neutral atom quantum computing experiments rely on destructive state detection techniques that eject the detected qubits from the trap. These techniques limit the repetition rate of these experiments due to the necessity of reloading a new quantum register for each operation.
We address this problem by developing reusable neutral atom qubits. Individual Rubidium 87 atoms are trapped in an optical lattice and are held for upwards of 300 s. Each atom is prepared in an initial quantum state and then the state is subsequently detected with 95% fidelity with less than a 1% probability of losing it from the trap. This combination of long storage times and nondestructive state detection will facilitate the development of faster and more complex quantum systems that will enable future advancements in the field of quantum information.
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Wang, Feng. "Modes, Excitation and Applications of Plasmonic Nano-apertures and Nano-cavities." Kent State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=kent1348588159.
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Richter, Johannes Martin. "Charge carrier relaxation in halide perovskite semiconductors for optoelectronic applications." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275568.
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Lead halide perovskites have shown remarkable device performance in both solar cells and LEDs. Whilst the research efforts so far have been mainly focussed on device optimisation, little is known about the photophysical properties. For example, the nature of the bandgap is still debated and an indirect bandgap due to a Rashba splitting has been suggested. In this thesis, we study the early-time carrier relaxation and its impact on photoluminescence emission. We first study ultrafast carrier thermalization processes using 2D electronic spectroscopy and extract characteristic carrier thermalization times from below 10 fs to 85 fs. We then investigate the early-time photoluminescence emission during carrier cooling. We observe that the luminescence signal shows a rise over 2 picoseconds in CH3NH3PbI3 while carriers cool to the band edge. This shows that luminescence of hot carriers is slower than that of cold carriers, as is found in direct gap semiconductors. We conclude that electrons and holes show strong overlap in momentum space, despite the potential presence of a small band offset arising from a Rashba effect. Recombination and device performance of perovskites are thus better described within a direct bandgap model. We finally study carrier recombination in perovskites and the impact of photon recycling. We show that, for an internal photoluminescence quantum yield of 70%, we measure external yields as low as 15% in planar films, where light out-coupling is inefficient, but observe values as high as 57% in films on textured substrates that enhance out-coupling. We study the photo-excited carrier dynamics and use a rate equation to relate radiative and non-radiative recombination events to measured photoluminescence efficiencies. We conclude that the use of textured active layers has the ability to improve power conversion efficiencies for both LEDs and solar cells.
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Zrir, Mohammad ali. "Tensile-strained and highly n-doped Germanium for optoelectronic applications." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4036/document.
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Dans le cadre de ce travail de thèse, nous avons étudié une approche permettant de réaliser les composants d'émission de la lumière basés sur les couches epitaxiées de Ge contraint en tension et fortement dopé de type n. Afin de créer de contrainte en tension dans les films épitaxiés de Ge, nous avons investi deux méthodes : faire croître du Ge sur InGaAs ayant un paramètre de maille plus grand que celui de Ge, et faire croître du Ge sur Si, en prenant l'avantage du coefficient de dilatation thermique du Ge, qui est deux fois plus grand que celui du Si. Concernant la croissance de Ge sur les substrats Si, nous avons étudié deux orientations cristallines, <001> and <111>, afin de pouvoir comparer la valeur de contrainte en tension obtenue et aussi la densité des dislocations émergeantes. Le dopage de type n dans le Ge a été effectué en utilisant le phosphore et l'antimoine. Nous avons montré que quand le dopage est effectué à des températures relativement basses et suivi d'un recuit thermique rapide, de concentration d'électrons électriquement activés de ~ 4x10^19 cm-3, a pu être obtenue. Cette valeur représente l'un des meilleurs résultats expérimentalement obtenus jusqu'à présent. Des mesures de recombinaison radiative par spectroscopie de photoluminescence effectuées à température ambiante ont mis en évidence une augmentation de l'émission du gap direct de Ge d'environ 150 fois. Finalement, nous avons étudié les effets de la barrière de diffusion sur l'efficacité de dopage pendant les recuits thermiques. Une comparaison sur l'efficacité de trois barrières de diffusion, Al2O3, HfO2 and Si3N4, sera présentée et discutéeDuring my thesis, we studied approaches to achieve light-emitting devices based on tensile strained and highly n-doped Ge epitaxial films. In order to create an elastic tensile strain in the epitaxial Ge films, we have investigated two methods: The epitaxial growth of Ge on InGaAs buffer layers that have a larger lattice constant, and the epitaxial growth of Ge on Si, by which we take benefit of the thermal expansion coefficient of Ge which is twice greater than that of Si. Concerning the growth of Ge on Si substrates, we have studied two crystalline orientations, <001> and <111>, in order to compare the values of the accumulated tensile strain and also the density of threading dislocations. The n-type doping in Ge was performed using a co-doping technique with phosphorus (P2 molecule) and antimony (Sb). We demonstrated that the dopants sticking coefficient leads to dopant incorporation in the Ge film larger than their solid solubility, which generally increases with increasing substrate temperature. As a result, when the doping is carried out at relatively low temperatures and followed by rapid thermal annealing, electrically activated electron concentration of 4x1019 cm-3 was demonstrated. This value is one of the best results obtained experimentally so far. The radiative recombination, at RT, measured by photoluminescence spectroscopy showed an increase in the direct gap emission of Ge of about 150 times. Finally, we studied the effects of diffusion barrier on the doping concentration during the thermal annealing. A comparison between the advantages of three diffusion barriers, Al2O3, HfO2 and Si3N4, will be presented and discussed
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Hajsaid, Marwan. "Photoresponse study of platinum silicide Schottky-barrier diodes and electrical characterization of porous silicon with some device applications /." free to MU campus, to others for purchase, 1996. http://wwwlib.umi.com/cr/mo/fullcit?p9717171.
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Cheung, Ka-yi, and 張嘉兒. "Optical parametric processes in biophotonics and microwave photonics applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45207835.
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Norton, Dennis Thomas Jr. "Type-II InAs/GaSb superlattice LEDs: applications for infrared scene projector systems." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/5031.
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Optoelectronic devices operating in the mid-wave (3-5 Μm) and long-wave (8-12 Μm) infrared (IR) regions of the electromagnetic spectrum are of a great interest for academic and industrial applications. Due to the lack of atmospheric absorption, devices operating within these spectral bands are particularly useful for spectroscopy, imaging, and dynamic scene projection. Advanced IR imaging systems have created an intense need for laboratory-based infrared scene projector (IRSP) systems which can be used for accurate simulation of real-world phenomena occurring in the IR. These IRSP systems allow for reliable, reproducible, safe, and cost-effective calibration of IR detector arrays. The current state-of-the-art technology utilized for the emitter source of IRSP systems is thermal pixel arrays (TPAs) which are based on thin film resistor technology. Thermal pixel array technology has fundamental limitations related to response time and maximum simulated apparent temperature, making them unsuitable for emulation of very hot (> 700 K) and rapidly evolving scenes.
Additionally, there exists a need for dual wavelength emitter arrays for IRSP systems dedicated to calibration of dual wavelength detector arrays. This need is currently met by combining the spectral output from two separate IRSP systems. This configuration requires precise alignment of the output from both systems and results in the maximum radiance being limited to approximately half that of the capability of a given emitter array due to the optics used to combine the outputs.
The high switching speed inherent to IR light-emitting diodes (LEDs) and the potential for high power output makes them an appealing candidate to replace the thermal pixel arrays used for IRSP systems. To this end, research has been carried out to develop and improve the device performance of IR LEDs based on InAs/GaSb type-II superlattices (T2SLs). A common method employed to achieve high brightness from LEDs is to incorporate multiple active regions, coupled by tunnel junctions. Tunnel junctions must provide adequate barriers to prevent carrier leakage, while at the same time remain low in tunneling resistance to prevent unwanted heating. The performance of two tunnel junction designs are compared in otherwise identical four stage InAs/GaSb superlattice LED (SLED) devices for application in IRSP systems.
This research culminated in the development of a 48 Μm pitch, 512$times512 individually addressable mid-wave IR LED array based on a sixteen stage, InAs/GaSb T2SL device design. This array was hybridized to a read-in integrated circuit and exhibited a pixel yield greater than 95 %. Projections based on single element emitter results predict this array will be able to achieve a peak apparent temperature of 1350 K within the entire 3-5 Μm band. These results demonstrate the feasibility of emitter arrays intended for IRSP systems based on InAs/GaSb SLED devices.
Additionally, a dual wavelength 48 Μm pitch, 8x8 emitter array based on InAs/GaSb T2SL LEDs was developed and demonstrated. This design incorporates two separate, 16 stage InAs/GaSb SL active regions with varying InAs layer thicknesses built into a single vertical heterostructure. The device architecture is a three terminal device allowing for independent control of the intensity of each emission region. Each emitter region creates a contiguous pixel, capable of being planarized and mated to drive electronics.
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Yang, Ying. "Organic semiconductor lasers : compact hybrid light sources and development of applications." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/2569.
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This thesis describes a number of studies on organic semiconductors as laser gain media with the aim of simplifying the excitation scheme and exploring potential applications. A hybrid device taking the advantage of high power inorganic light emitting diodes (LEDs) and low threshold organic distributed feedback lasers is demonstrated to realize a LED pumped organic laser. When the drive current is higher than 152 A, a sharp peak is clearly observed in the laser output spectrum, implying the LED successfully pumps the polymer laser above threshold. This is the first time an incoherent LED has been used as the excitation source for an organic semiconductor laser. A strategy for further improving the performance of the hybrid device is explored with the use of a luminescent concentrator made of a dye doped SU8 film, to intensify the power density from the inorganic LED. The luminescent concentrator is capable of increasing the incident power density by a factor of 9 and reducing the lasing threshold density by 4.5 times. As a preliminary investigation towards mode-locked polymer lasers, the impact of a solid state saturable absorber on a solution based organic semiconductor laser is explored. The dye doped polystyrene thin film saturable absorber exhibits a saturation intensity of a few MW/cm². When it is placed into the laser cavity, a train of short pulses is generated and the underlying mechanism is discussed. Finally, the potential of using organic semiconductor lasers in the detection of nitro-aromatic explosive vapours is studied in distributed feedback polyfluorene lasers. A high sensing efficiency and fast response from the laser prove polyfluorene lasers can be used as disposal and low cost devices in explosive chemosensing.
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Schnabel, Manuel. "Silicon nanocrystals embedded in silicon carbide for tandem solar cell applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:da5bbb64-0bcd-4807-a9f3-4ff63a9ca98d.
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Tandem solar cells are potentially much more efficient than the silicon solar cells that currently dominate the market but require materials with different bandgaps. This thesis presents work on silicon nanocrystals (Si-NC) embedded in silicon carbide (SiC), which are expected to have a higher bandgap than bulk Si due to quantum confinement, with a view to using them in the top cell of a tandem cell. The strong photoluminescence (PL) of precursor films used to prepare Si-NC in SiC (Si-NC/SiC) was markedly reduced upon Si-NC formation due to simultaneous out-diffusion of hydrogen that passivated dangling bonds. This cannot be reversed by hydrogenation and leads to weak PL that is due to, and limited by, non-paramagnetic defects, with an estimated quantum yield of ≤5×10-7. Optical interference was identified as a substantial artefact and a method proposed to account for this. Majority carrier transport was found to be Ohmic at all temperatures for a wide range of samples. Hydrogenation decreases dangling bond density and increases conductivity up to 1000 times. The temperature-dependence of conductivity is best described by a combination of extended-state and variable-range hopping transport where the former takes place in the Si nanoclusters. Furthermore, n-type background doping by nitrogen and/or oxygen was identified. In the course of developing processing steps for Si-NC-based tandem cells, a capping layer was developed to prevent oxidation of Si-NC/SiC, and diffusion of boron and phosphorus in nanocrystalline SiC was found to occur via grain boundaries with an activation energy of 5.3±0.4 eV and 4.4±0.7 eV, respectively. Tandem cells with a Si-NC/SiC top cell and bulk Si bottom cell were prepared that exhibited open-circuit voltages Voc of 900 mV and short-circuit current densities of 0.85 mAcm-2. Performance was limited by photocurrent collection in the top cell; however, the Voc obtained demonstrates tandem cell functionality.
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VOHRA, VARUN. "Multilevel organization of hybrid materials based on zeolite L crystals for light emitting devices applications." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2009. http://hdl.handle.net/10281/7549.
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Zeolite L has been shown to be a successful host material for preparing a large variety of inorganic/organic hybrids. The channel entrances of the zeolite L are of a diameter of 0,71 nm and therefore, by tuning the size and the shape of the organic guest, one can make those guests enter one by one due to size restrictions. Once in the channels, well chosen dye molecules stay separated one from another which leads to a higher photoluminescence quantum yield.
A challenge concerning such host guest compounds is to be able to optically or electronically address the dye inside the zeolite channels. Another interesting feature is to obtain organised functional hybrid thin films with a high concentration of non aggregated dye loaded zeolite L crystals and to use those thin films as active layers for devices such as light emitting diodes (LED). Some of these systems lead to very efficient two step energy transfers from the conjugated polymer to the dye included inside the inorganic host. New perspectives for the fabrication of novel devices based on zeolite L crystals can be introduced through using those systems which could have an enormous potential in the fields of lighting, and displays but also to mimic the energy conversion process during photosynthesis.
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Cheung, Chor-keung. "The construction of a focused low energy positron beam facility and its application in the study of various optoelectronic materials." View the Table of Contents & Abstract, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36995770.
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Ego, Christophe. "Oligo and polyfluorenes of controlled architecture for applications in opto-electronics." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210958.
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Polyfluorenes are polymers with outstanding properties: They are semi-conducting, relatively rigid, quite stable chemically and thermally, easily substituted and therefore potentially soluble in numerous solvents and more importantly, they exhibit blue electro- and photoluminescence. For all these reasons, these polymers are the subjects of numerous academic and industrial researches.The first subject of this work deal with the design, the synthesis and the characterisation of polyfluorenes end-capped with perylene dicarboximide derivatives. These perylene moieties are able to interact by energy transfer under specific conditions of illumination, proximity and orientation. Their observation by single molecule spectroscopy permitted therefore to gain valuable information concerning the three-dimensional folding of single polyfluorene chains. To complete this study, the synthesis and characterisation of a perylene end-capped trimer of fluorene was performed. This structure being monodisperse, a finer analysis of the energy-transfer occurring between both perylene dyes could be accomplished, which confirmed the structural hypothesis made for the polymer. During these studies, it has been observed that, in addition to the energy transfer occurring between both perylene derivatives, another energy transfer occurs between the polyfluorene backbone and the perylene derivatives upon excitation of the first. This led to the idea of the synthesis of a polyfluorene bearing perylenes dicarboximide as side chains. This perylene-rich polyfluorene has been used to build a photovoltaic cell efficient in the wavelengths of both polyfluorene absorption and perylene carboximide absorption.
Another subject of this work was the design, synthesis and characterisation of polyfluorenes bearing bulky phenoxy groups as side-chains. These polymers, due to their lower tendency toward aggregation, exhibited a better stability of their emission colour upon annealing. Similarly, a series of homo- and copolymers of fluorene bearing bulky and hole accepting triphenylamine substituants was synthesised and characterised. In addition to their improved colour stability in comparison with dialkylpolyfluorenes, the LEDs build with these materials exhibited a very low turn on voltage.
Doctorat en sciences, Spécialisation chimie
info:eu-repo/semantics/nonPublished
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Cheung, Chor-keung, and 張初強. "The construction of a focused low energy positron beam facility and its application in the study of various optoelectronic materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37434925.
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Gorbenko, Viktoriia. "Caractérisation par faisceaux d’ions d’hétérostructures III-V pour les applications micro et optoélectroniques." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT140/document.
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L'intégration de composés semi-conducteurs III-V sur silicium devrait conduire au développement de nouveaux dispositifs micro- et optoélectroniques performants. Le composé InGaAs de haute mobilité électronique est un candidat prometteur pour le transistor métal-oxyde-semiconducteur à effet de champ à canal n au-delà du noeud technologique 10 nm. En outre les semi-conducteurs III-V sont aussi des matériaux appropriés pour la fabrication de composants optiques (lasers, diodes) et de dispositifs analogiques ultra-haute fréquence et leur intégration sur une plateforme Si ajoutera de nouvelles fonctionnalités pour le réseau de communications optiques. Cependant la miniaturisation des dispositifs et leur intégration dans les architectures 3D nécessitent le développement de méthodes de caractérisation avancées pour fournir des informations sur leur composition physico-chimique avec une résolution à l'échelle nanométrique.Dans cette thèse, les études physico-chimiques des hétérostructures III-V directement élaborées sur plaquettes de Si 300 mm par épitaxie en phase vapeur sont adressées. Les techniques de spectrométrie de masse d'ions secondaires sont utilisées et développées dans le but d'étudier la raideur des interfaces, la composition chimique et le dopage de couches III-V minces dans des architectures 2D et 3D avec une bonne résolution en profondeur. L'analyse quantitative précise sur un puits quantique InGaAs (PQ) pour des architectures 2D et 3D a été réalisée en utilisant les techniques SIMS magnétique et Auger. Pour obtenir le profil chimique des structures III-V étroites et répétitives, une méthode de moyenne des profils a été développée pour ces deux techniques. Egalement, la reconstruction 3D et le profil en profondeur de tranchées individuelles (moins de cent nanomètres de largeur) contenant un PQ d’InGaAs mince obtenu par croissance sélective dans des cavités de dioxyde de silicium en utilisant la méthode de piégeage des défauts par rapport d’aspect ont été obtenus avec succès en utilisant le SIMS à temps de vol ainsi que la sonde atomique tomographique. Enfin, les résultats ont été corrélés avec des mesures de photoluminescenceThe integration of III-V semiconductor compounds on silicon should lead to the development of new highly efficient micro- and opto-electronic devices. High mobility InGaAs material is a promising candidate for n-channel metal-oxide semiconductor field-effect transistor beyond the 10 nm technology node. Moreover III-V semiconductors are also suitable materials for fabrication of optical (lasers, diodes) and ultra-high frequency analog devices and their integration on a Si platform will add new functionalities for optical network and communication. However the miniaturization of devices and their integration into 3D architectures require the development of advanced characterization methods to provide information on their physico-chemical composition with nanometer scale resolution.In this thesis, the physico-chemical studies of III-As heterostructures directly grown on 300 mm Si wafers by metalorganic vapor phase epitaxy are addressed. Secondary ion mass spectrometry techniques are used and developed in order to study interfaces abruptness, chemical composition and doping of III-V thin layers in 2D and 3D architectures with high depth resolution. The accurate quantitative analysis on InGaAs quantum wells (QWs) in 2D and 3D architectures was performed using magnetic SIMS and Auger techniques. To obtain the chemical profiling of narrow and repetitive III-V structures the averaging profiling method was developed for both techniques. Additionally, 3D reconstruction and depth profiling of individual trenches (less than hundred nanometer in width) containing thin InGaAs QWs selectively grown in silicon dioxide cavities using the aspect ratio trapping method were successfully obtained using Time-of-flight SIMS and atom probe tomography. Finally, the results were correlated with photoluminescence measurements
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Kovacik, Peter. "Vacuum deposition of organic molecules for photovoltaic applications." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:98461a90-5ae3-4ae3-9245-0f825adafa72.
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Organic photovoltaics have attracted considerable research and commercial interest due to their lightness, mechanical flexibility and low production costs. There are two main approaches for the fabrication of organic solar cells – solution and vacuum processing. The former relies on morphology control in polymer-fullerene blends resulting from natural phase separation in these systems. The latter takes advantage of solvent-free processing allowing highly complex multi-junction architectures similar to inorganic solar cells. This work aims to combine the benefits of both by depositing conjugated polymers using vacuum thermal evaporation. By employing this unconventional approach it aims to enhance the efficiency of organic photovoltaics through increased complexity of the thin-film architecture while improving the nanoscale morphology control of the individual active layers. The thesis explores the vacuum thermal deposition of polythiophenes, mainly poly(3-hexylthiophene) (P3HT) and side-group free poly(thiophene) (PTh). A variety of chemical techniques, such as NMR, FT-IR, GPC, DSC and TGA, are used to examine the effect of heating on chemical structure of the polymers. Optimal processing parameters are identified and related to the resulting thin-film morphology and charge transport properties. Efficient photovoltaic devices based on polythiophene donors and fullerene acceptors are fabricated. Materials science techniques AFM, XRD, SEM, TEM and MicroXAM are used to characterize topography and morphology of the thin films, and UV-Vis, EQE, I-V and C-V measurements relate these to the optical and electronic properties. The results of the study show that polymer side groups have a strong influence on molecular packing and charge extraction in vacuum-deposited polymer thin films. Unlike P3HT, evaporated PTh forms highly crystalline films. This leads to enhanced charge transport properties with hole mobility two orders of magnitude higher than that in P3HT. The effect of molecular order is demonstrated on polymer/fullerene planar heterojunction solar cells. PTh-based devices have significantly better current and recombination characteristics, resulting in improved overall power conversion efficiency (PCE) by 70% as compared to P3HT. This confirms that the chemical structure of the molecule is a crucial parameter in deposition of large organic semiconductors. It is also the first-ever example of vacuum-deposited polymer photovoltaic cell. Next, vacuum co-deposited PTh:C60 bulk heterojunctions with different donor-acceptor compositions are fabricated, and the effect of post-production thermal annealing on their photovoltaic performance and morphology is studied. Co-deposition of blended mixtures leads to 60% higher photocurrents than in thickness-optimized PTh/C60 planar heterojunction counterparts. Furthermore, by annealing the devices post-situ the PCE is improved by as much as 80%, achieving performance comparable to previously reported polythiophene and oligothiophene equivalents processed in solution and vacuum, respectively. The enhanced photo-response is a result of favourable morphological development of PTh upon annealing. In contrast to standard vacuum-processed molecular blends, annealing-induced phase separation in PTh:C60 does not lead to the formation of coarse morphology but rather to an incremental improvement of the already established interpenetrated nanoscale network. The morphological response of the evaporated PTh within the blend is further verified to positively differ from that of its small-molecule counterpart sexithiophene. This illustrates the morphological advantage of polymer-fullerene combination over all other vacuum-processable material systems. In conclusion, this processing approach outlines the conceptual path towards the most beneficial combination of solution/polymer- and vacuum-based photovoltaics. It opens up a fabrication method with considerable potential to enhance the efficiency of large-scale organic solar cells production.
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Das, Aparna. "Boîtes quantiques de semi-conducteurs nitrures pour des applications aux capteurs opto-chimiques." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00870365.
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Ce travail de thèse a porté sur la synthèse de boîtes quantiques (BQs) de semi-conducteurs nitrures orientés (11-22) ou (0001) par épitaxie par jets moléculaires à plasma d'azote, pour des applications aux capteurs chimiques pour la détection du niveau de pH, d'hydrogène ou des hydrocarbures dans des environnements gazeux ou liquides. Dans la première partie de ce manuscrit, je décri la synthèse des couches bidimensionnelles semi-polaires (11-22) : des couches binaires (AlN, GaN, and InN) et des ternaires (AlGaN et InGaN), qui sont requises pour le contact de référence dans les transducteurs et aussi pour établir une connaissance de base pour comprendre la transition dès la croissance bidimensionnelle à la croissance tridimensionnel des BQs. Un résultat particulièrement relevant est l'étude de la cinétique de croissance et l'incorporation de l'indium dans les couches d'InGaN(11-22). De même que pour InGaN polaire (0001), les conditions optimales de croissance pour l'orientation cristallographique semi-polaire correspondent à la stabilisation de 2 ML d'In sur la surface, en excellent accord avec des calculs théoriques. Les limites de la fenêtre de croissance en termes de température du substrat et de flux d'In sont les mêmes pour les matériaux semi-polaire et polaires. Cependant, j'ai constaté une inhibition de l'incorporation de l'In dans les couches semi-polaires, même pour une température en dessous du seuil de la ségrégation pour l'InGaN polaire. Dans une deuxième étape, j'ai fabriqué des super-réseaux de BQs de GaN/AlN et InGaN/GaN, à la fois dans l'orientation polaire et semi-polaire. Les mesures de photoluminescence et de photoluminescence en temps résolu confirment la réduction du champ électrique interne dans les boîtes semi-polaires. D'autre part, les BQs semi-polaires à base d'InGaN doit relever le défi de l'incorporation d'In dans cette orientation cristallographique. Pour surmonter ce problème, l'influence de la température de croissance sur les propriétés des boîtes quantiques InGaN polaires et semi-polaires a été étudiée, en considérant la croissance à haute température (TS = 650-510 °C, où la désorption d'In est active) et à basse température (TS = 460-440 °C, où la désorption d'In est négligeable). J'ai démontré que les conditions de croissance à faible TS ne sont pas compatibles avec le plan polaire, tandis qu'ils fournissent un environnement favorable au plan semi-polaire pour améliorer l'efficacité quantique interne de nanostructures InGaN. Enfin, j'ai synthétisé un certain nombre de transducteurs à BQs de GaN/AlN et InGaN/GaN selon les axes de croissance polaire et semi-polaire. Dans chaque cas, les conditions de croissance pour atteindre la fourchette spectrale ciblée (420-450 nm d'émission à avec une couche contact transparente pour des longueurs d'onde plus courtes que 325 nm) ont été identifiés. L'influence d'un champ électrique externe sur la luminescence des transducteurs ont confirmé que la meilleure performance (plus grande variation de la luminescence en fonction de la polarisation) a été fournie par des structures à base de BQs d'InGaN/GaN. Avec ces données, les spécifications des transducteurs opto-chimiques ont été fixées : 5 perides de BQs d'InGaN/GaN sur une couche contact d'Al0.35Ga0.65N:Si). Puis, j'ai synthétisé un certain nombre de ces transducteurs afin d'obtenir un aperçu sur la reproductibilité, limites et les étapes critiques du processus de fabrication. En utilisant ces échantillons, nous avons réalisé un système capteur intégré qui a été utile pour le suivi de la valeur du pH de l'eau.
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Coronel-Rico, Juan Fernando. "Étude et réalisation d'un oscillateur à base de VCSEL verrouillé en phase pour des applications en télécommunications." Thesis, Toulouse, ISAE, 2016. http://www.theses.fr/2016ESAE0013/document.
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Les oscillateurs sont présents dans tous les systèmes de communications que nous utilisons. Ils nous permettent de faire la synchronisation entre l’émetteur et le récepteur d’un message. La qualité de cette synchronisation dépend de la stabilité de l’oscillateur. Afin de caractériser cette stabilité dans le domaine fréquentiel, le bruit de phase est utilisé comme paramètre de référence. Un oscillateur qui délivre un signal avec une faible valeur de bruit de phase est un oscillateur de grande pureté spectrale. Les oscillateurs électroniques ont une bonne performance à basse fréquence. En mesure de la demande des systèmes de très haut débit, les oscillateurs électroniques ne sont pas capables de produire signaux qu’avec l’utilisation de multiplicateurs de fréquence qui ajoutent plusieurs éléments à la chaine de communication. Les systèmes hybrides permettent de prendre d’avantage la bonne performance de composants optiques en haute fréquence afin de les intégrer dans les systèmes électroniques et surmonter de cette façon-là les limitations fréquentielles des systèmes électroniques. Ce travail vise l’utilisation de la technique de verrouillage optique par injection du faisceau d’un laser maître vers la cavité d’un VCSEL sous modulation directe dans la boucle d’oscillation. La technique du verrouillage optique du VCSEL permets d’élargir la bande passante de modulation directe du VCSEL et réduire son bruit d’intensité (Relative Intensity Noise - RIN). La réduction du RIN a comme effet secondaire la réduction de la contribution du bruit additif dans l’oscillateur et, en conséquence, la réduction du bruit de phase de l’oscillateurOscillators are present in all telecommunication systems. They synchronize the emitter and receiver of a message. The quality of the synchronization depends on the oscillator stability. To characterize the frequency domain oscillator stability, the phase noise of the carrier is used as figure of merit. An oscillator delivering a low phase noise carrier is a high spectral purity oscillator. Electronic oscillators are high performing at low frequencies. As communications systems require high data rate transmission, the electronic oscillators uses frequency multipliers that degrades the spectral purity of the carrier. The hybrid systems take advantage of the good performance of optical components at high frequency with the goal to be integrated in the electronic systems to overcome frequency limitation issues. This work use the optical injection locking technique by injecting the laser beam of a master laser inside the cavity of a VCSEL under direct modulation. The optical injection locking technique enlarges the direct modulation bandwidth of the VCSEL and reduces the Relative Intensity noise of the laser (RIN). The RIN reduction has as side effect the reduction of the additive noise inside the oscillator and, in consequence, reducing the oscillator phase noise
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Greul, Enrico [Verfasser], and Thomas [Akademischer Betreuer] Bein. "On the way to non-toxic and highly stable perovskite-based optoelectronics : synthesis and investigations of lead-free perovskites for photovoltaic applications / Enrico Greul ; Betreuer: Thomas Bein." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/119109815X/34.
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