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Buzzo, Marco. "Dopant imaging and profiling of wide bandgap semiconductor devices /." Konstanz : Hartung-Gorre, 2007. http://www.loc.gov/catdir/toc/fy0715/2007427206.html.
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Farahmand, Maziar. "Advanced simulation of wide band gap semiconductor devices." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/14777.
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Schwarz, Casey Minna. "Radiation Effects on Wide Band Gap Semiconductor Transport Properties." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5488.
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In this research, the transport properties of ZnO were studied through the use of electron and neutron beam irradiation. Acceptor states are known to form deep in the bandgap of doped ZnO material. By subjecting doped ZnO materials to electron and neutron beams we are able to probe, identify and modify transport characteristics relating to these deep accepter states. The impact of irradiation and temperature on minority carrier diffusion length and lifetime were monitored through the use of the Electron Beam Induced Current (EBIC) method and Cathodoluminescence (CL) spectroscopy. The minority carrier diffusion length, L, was shown to increase as it was subjected to increasing temperature as well as continuous electron irradiation. The near-band-edge (NBE) intensity in CL measurements was found to decay as a function of temperature and electron irradiation due to an increase in carrier lifetime. Electron injection through application of a forward bias also resulted in a similar increase of minority carrier diffusion length. Thermal and electron irradiation dependences were used to determine activation energies for the irradiation induced effects. This helps to further our understanding of the electron injection mechanism as well as to identify possible defects responsible for the observed effects. Thermal activation energies likely represent carrier delocalization energy and are related to the increase of diffusion length due to the reduction in recombination efficiency. The effect of electron irradiation on the minority carrier diffusion length and lifetime can be attributed to the trapping of non-equilibrium electrons on neutral acceptor levels. The effect of neutron irradiation on CL intensity can be attributed to an increase in shallow donor concentration. Thermal activation energies resulting from an increase in L or decay of CL intensity monitored through EBIC and CL measurements for p-type Sb doped ZnO were found to be the range of Ea = 112 to 145 meV. P-type Sb doped ZnO nanowires under the influence of temperature and electron injection either through continuous beam impacting or through forward bias, displayed an increase in L and corresponding decay of CL intensity when observed by EBIC or CL measurements. These measurements led to activation energies for the effect ranging from Ea = 217 to 233 meV. These values indicate the possible involvement of a SbZn-2VZn acceptor complex. For N-type unintentionally doped ZnO, CL measurements under the influence of temperature and electron irradiation by continuous beam impacting led to a decrease in CL intensity which resulted in an electron irradiation activation energy of approximately Ea = 259 meV. This value came close to the defect energy level of the zinc interstitial. CL measurements of neutron irradiated ZnO nanostructures revealed that intensity is redistributed in favor of the NBE transition indicating an increase of shallow donor concentration. With annealing contributing to the improvement of crystallinity, a decrease can be seen in the CL intensity due to the increase in majority carrier lifetime. Low energy emission seen from CL spectra can be due to oxygen vacancies and as an indicator of radiation defects.ID: 031001520; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Advisers: Elena Flitsiyan, Leonid Chernyak.; Title from PDF title page (viewed August 19, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 104-109).
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Fay, Michael W. "Advanced electron microscopy of wide band-gap semiconductor materials." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340213.
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Martin, Aude. "Nonlinear Photonic Nanostructures based on Wide Gap Semiconductor Compounds." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS526/document.
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La consommation d’énergie liée aux technologies de l’information augmente trèsrapidement et dans la mesure où la société a besoin d’être toujours plus connectée tout ens’appuyant sur des solutions durables, les technologies actuelles ne suffisent plus. La photoniqueintégrée s’impose dès lors comme une alternative à l’électronique pour réaliser du traitementdu signal économe en énergie. Au cours de cette thèse, j’ai étudié des structures sub-longueurd’onde en semiconducteur, les cristaux photoniques, qui présentent des propriétés non linéairesimpressionnantes. Plus précisément, le confinement fort et la propagation en lumière lente permettentun traitement sur puce de signal ultra-rapide tout optique, soit à partir de mélange àquatre ondes ou d’auto-modulation de phase. L’originalité est l’utilisation de nouveaux matériauxsemi-conducteurs ayant moins d’absorption non linéaires et par porteurs libres, effets qui limitentla pleine exploitation des effets non linéaires dans les structures photoniques en Silicium. Dansma thèse, des semiconducteurs III-V ont été utilisés pour développer des guides et des cavitéscristal photonique de grande qualité qui sont en mesure de supporter des densités de puissanceoptiques extrêmement élevées ainsi que de grands niveaux de puissance moyenne. J’ai amélioré laconductivité thermique des guides d’ondes grâce à l’intégration hétérogène de membranes GaInPavec du dioxyde de silicium. Cette plateforme permettra à terme de démontrer de l’amplificationsensible à la phase dans le régime continu que j’ai déjà démontré dans le régime pulsé en utilisant des membranes suspendues en GaInP. En parallèle, j’ai démontré des cristaux photoniques de grande qualité dans du Gallium phosphure, qui est un matériau très prometteur en raison de lagrande bande interdite et de la très bonne conductivité thermique. Les résultats préliminaires ontpermis la réalisation d’un régime non linéaire intense (mini-peigne de fréquence, compression etfission de soliton ...)The energy consumption of the whole ICT ecosystem is growing at a fast paceand in a global context of the search for an ever more connected yet sustainable society, a technologicalbreakthrough is desired. Here, integrated nonlinear photonics will help by providingnovel possibilities for energy efficient signal processing. In this PhD thesis, I have been investigatingsub-wavelength semiconductor structures, particularly photonic crystals, which have shownremarkable nonlinear properties. More specifically the strong confinement and slow light propagationenables on-chip ultra-fast all-optical signal processing, either based on four-wave-mixingor self-phase modulation. The main point here is the use of novel semiconductor materials withimproved nonlinear properties with respect to Silicon. In fact, it has now been acknowledgedthat the nonlinear and free-carriers absorption in Silicon integrated photonic structures is anissue hindering the full exploitation of nonlinear effects. In my thesis, wide-gap III-V semiconductorshave been used to develop high quality photonic crystal waveguides and cavities whichare able to sustain extremely high optical power densities as well as large average power levels.I have demonstrated PhC waveguides with much improved thermal conductivity through heterogeneousintegration of GaInP membranes with silicon dioxide. This will allow continuous wave phase-sensitive amplification, which I already demonstrated in the pulsed regime using GaInPself-suspended membranes. In parallel, I have demonstrated high quality PhC in Gallium Phosphide,which is a very promising material because of the large bandgap and the very good thermalconductivity. Preliminar results demonstrate the achievement of extremely large nonlinear regime(mini-comb, soliton compression and fission ...)
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Bellotti, E. (Enrico). "Advanced modeling of wide band gap semiconductor materials and devices." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/15354.
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Orange, Catherine Louise. "Spin-flip Raman scattering of wide band gap semiconductor heterostructures." Thesis, University of East Anglia, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267773.
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Sodipe, Olukayode O. "Wide-band Gap Devices for DC Breaker Applications." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1529.
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With the increasing interest in wide-band gap devices, their potential benefits in power applications have been studied and explored with numerous studies conducted for both SiC and GaN devices. This thesis investigates the use of wide-band gap devices as the switching element in a semiconductor DC breaker. It involves the design of an efficient semiconductor DC breaker, its simulation in SPICE, construction of a hardware prototype and the comparative study of SiC and Si versions of the aforementioned breaker. The results obtained from the experiments conducted in the process of concluding this thesis show that the SiC version of the breaker is a superior option for a semiconductor DC breaker.
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Lajn, Alexander. "Transparent rectifying contacts on wide-band gap oxide semiconductors." Doctoral thesis, Universitätsbibliothek Leipzig, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-102799.
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Die vorliegenden Arbeit befasst sich mit der Herstellung und Charakterisierung von transparenten Metall-Halbleiter- Feldeffekttransistoren. Dazu werden im ersten Kapitel
transparente gleichrichtende Kontakte, basierend auf dem Konzept von Metalloxidkontakten, hergestellt und im Hinblick auf chemische Zusammensetzung des Kontaktmaterials, Barriereninhomogenität und Kompatibilität mit amorphen Halbleitern untersucht. Außerdem wird die
Anwendbarkeit der Kontakte als UV-Sensor studiert. Im zweiten Kapitel werden transparente leitfähige Oxide vorgestellt und insbesondere deren optische und elektrische Eigenschaften
in Abhängigkeit von den Herstellungsbedingungen studiert. Das dritte Kapitel beinhaltet Untersuchungen zu transparenten Feldeffektransistoren, die auf den im ersten Kapitel untersuchten transparenten gleichrichtenden Kontakten basieren (TMESFETs). Insbesondere die elektrischen Stabilität der Bauelemente hinsichtlich Beleuchtung, erhöhten Temperaturen und Spannungsstress wird untersucht. Auch die Langzeitstabilität, Reproduzierbarkeit und der
Effekt gepulster Spannungen wird betrachtet. Weiterhin wird die Verwendung amorpher Halbleiter im Kanal und damit auch die Herstellung flexibler Transistoren auf Folie demonstriert.
Zuletzt werden die TMESFETs integriert und als Inverterschaltkreise aufgebaut und untersucht. Außerdem wird die Eignung der Transistoren zur Messung von Aktionspotentialen von Nervenzellen studiert.
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Mayrock, Oliver. "Localization, disorder, and polarization fields in wide-gap semiconductor quantum wells." Doctoral thesis, [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=96140437X.
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Garner, D. M. "Silicon heterojunction bipolar transistors with wide band-gap amorphous semiconductor emitters." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599324.
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Firstly, the motivation behind the silicon HBT is discussed, followed by an investigation of tetrahedral amorphous carbon (ta-C) as a possible heteroemitter material. Silicon HBTs with n-type ta-C as a heteroemitter in npn transistors were studied first. Transistor action occurred, but the current gain was only 10-6. This was found to be due to the low electron affinity of ta-C creating a barrier to electron injection into the base, opposite to how an HBT should behave. The low electron affinity of ta-C motivated the fabrication of pnp transistors with p-type ta-C as the heteroemitter. These performed better, having a current gain approaching unity. The lack of thorough investigation of the silicon HBT with an amorphous silicon (a-Si:H) heteroemitter prompted an investigation into the static and dynamic characteristics of this device. Numerical simulation using device modelling software such as MEDICI is well-established for crystalline semiconductor materials but less so for amorphous materials. Therefore a physics-based model for a a-Si:H was incorporated into MEDICI and used to model the a-Si: emitter HBT under a range of collector and base dopings. The main observation from this work was that the low drift mobility of a-Si:H was a major impediment on its frequency response, limiting it to only 2.6GHz. The heteroemitter material properties were then varied to study their effect on transistor dynamic and static characteristics. The requirements on heteroemitter material parameters were found which produced a silicon HBT with superior performance to a silicon homojunction bipolar transistor. Silicon HBTs with a-Si:H emitters were fabricated, and the experimental characteristics compared well with the stimulations, verifying the a-Si:H model and the use of device simulation software to calculate the characteristics of silicon HBTs with amorphous emitters. Finally, a new 'pseudo'-HBT (PHBT) structure which has an n-type doped crystalline silicon emitter region between the heteroemitter material and the p-type base was elucidated and studied. This was found to increase the maximum cutoff frequency using an a-Si:H as the heteroemitter material from 2.8GHz to 6.4GHz.
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Ni, Ze. "Wide Band-Gap Semiconductor Based Power Converter Reliability and Topology Investigation." Diss., North Dakota State University, 2020. https://hdl.handle.net/10365/31935.
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Wide band-gap semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) have been widely investigated these years for their preferred operation at higher switching frequency, higher blocking voltage, higher temperature, with a compacter volume, in comparison with the traditional silicon (Si) devices. SiC MOSFETs have been utilized in photovoltaic systems, wind turbine converters, electric vehicles, solid-state transformers, more electric ships, and airplanes. GaN based transistors have also been adopted in the DC-to-DC converters in data centers, personal computers, AC-to-DC power factor correction converters for the consumer electronic adaptors, and DC-to-AC photovoltaic micro-inverters.
The first part of this dissertation is regarding the lifetime modeling and condition monitoring for the SiC MOSFETs. Since SiC-based devices have different failure modes and mechanisms compared with Si counterparts, a comprehensive review will be conducted to develop accurate lifetime prediction, condition monitoring, and lifetime extension strategies. First, a novel comprehensive online updated system-level lifetime modeling approach will be presented. Second, to monitor the SiC MOSFET ageing, the typical degradation indicators of SiC MOSFET gate oxide will be investigated. Third, to measure the junction temperature, the dynamic temperature-sensitive electrical parameters for the medium-voltage SiC devices will be studied.
The other part is the topology investigation of these emerging wide band-gap devices. A generalized topology that would leverage the advantages of the wide band-gap devices will be introduced and analyzed in detail. Following it is a new evaluation index for comparing different topologies with the consideration of the semiconductor die information. The topology and its derivatives will be utilized in the subsequent chapters for three applications. First, a 100 kW switched tank converter (STC) will be designed using SiC MOSFETs for transportation power electronic systems. Second, an updated STC topology integrating with the partial-power voltage regulation will be introduced for electric vehicle applications. Third, two novel single-phase resonant multilevel modular boost inverters will be designed based on the voltage-regulated STC. These topologies will be validated through designed prototypes. As a result, the high power density and high efficiency will be realized by combining the well-suited topologies and the advantages of the WBG devices.
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Brown, Graeme. "Time-resolved ultrafast spectroscopy of wide-gap II-VI semiconductor quantum wells." Thesis, Heriot-Watt University, 2001. http://hdl.handle.net/10399/502.
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Ouyang, Qiqing Christine. "Physical model enhancement and exploration of bandgap engineering in novel sub-100nm pMOSFETs /." Digital version:, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p9992880.
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Barnett, Anna Megan. "Wide band gap compound semiconductor detectors for x-ray spectroscopy in harsh environments." Thesis, University of Leicester, 2012. http://hdl.handle.net/2381/10375.
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Novel photon counting Alo.8Gao.2As, GaAs and SiC X-ray photodiodes were investigated through experiments and Monte Carlo computer simulations for their suitability as spectroscopic soft (:S 25 keY) X-ray detectors in high temperature (up to 90 QC) environments. Photon counting Alo.8Gao.2As and GaAs non-avalanche p+-i-n+ mesa X-ray photodiodes were shown to operate at temperatures as high as 90 QC. The temperature dependences of their spectral resolutions (FWHM at 5.9 keY) are reported. Analyses of the noise sources contributing to the devices' measured performances are presented which suggest that efforts to improve the spectral resolutions would be well targeted at reducing the noise contributions from the packaging of the detectors. For the GaAs diodes, the X-ray characterisation of the devices was extended to higher energies (25 keY). Internal detector X-ray fluorescence was demonstrated and Monte Carlo computer simulations were compared with the experimental results. Prior to the research presented in this thesis, the only Alo.8Gao.2As photon counting X-ray avalanche photodiodes reported in the literature (Lees et al., 2008, Nucl. Instr. and Meth. A, Vol. 594, pp. 202-205) had shown anomalies in the obtained spectra. Through new experimental measurements and computer simulations, the anomaly is explained. A new method was developed which uses the phenomenon to extract measurements of the electron and hole ionisation coefficients of Alo.8Gao.2As at a typical operating field and the first report of their temperature dependence is made. Measurements characterising the X-ray spectroscopic performance of Semi-Transparent SiC Schottky Diodes over an energy range ~6 keY to 25 keY at temperatures up to 80 QC are presented and discussed, along with relative efficiency measurements and data showing the temperature dependence of the leakage current in such devices. The research presented in this thesis shows that Alo.8Gao.2As, GaAs and SiC X-ray detectors are promising devices for high temperature soft X-ray spectroscopy.
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Klar, Peter Jens. "Magneto-optical studies of wide-gap dilute magnetic semiconductor heterostructures and quantum dots." Thesis, University of East Anglia, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338223.
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Zhang, Zhichun. "Process Dependence of Defects and Dopants in Wide Band Gap Semiconductor and Oxides." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366107518.
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Vandersand, James Dennis. "Growth of 6H-SiC homoepitaxy on substrates off-cut between the [01-10] planes." Master's thesis, Mississippi State : Mississippi State University, 2002. http://library.msstate.edu/etd/show.asp?etd=etd-11072002-095154.
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Piquette, Eric C. McGill T. C. "Molecular beam heteroepitaxial growth and characterization of wide band gap semiconductor films and devices /." Diss., Pasadena, Calif. : California Institute of Technology, 1999. http://resolver.caltech.edu/CaltechETD:etd-11292006-152956.
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Johnson, Jared M. "Atomic Scale Characterization of Point Defects in the Ultra-Wide Band Gap Semiconductor β-Ga2O3." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1577916628182296.
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Jadwisieńczak, Wojciech M. "The luminescence properties of the wide bandgap nitrides doped with rare earth ions and gallium nitride doped with conventional isoelectronic impurities." Ohio : Ohio University, 2001. http://www.ohiolink.edu/etd/view.cgi?ohiou1179158888.
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Bakarezos, Efthimios. "Ultrafast nonlinear optics of wide-gap II-VI quantum wells and polymeric materials." Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/519.
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Yao, Chengcheng Yao. "Semiconductor Galvanic Isolation Based Onboard Vehicle Battery Chargers." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1513586255613963.
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Armstrong, Andrew M. "Investigation of deep level defects in GaN:C, GaN:Mg and pseudomorphic AlGaN/GaN films." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1164038818.
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Flitcroft, Richard M. "Wide bandgap collector III-V double heterojunction bipolar transistors." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341875.
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Hiramatsu, Hidenori, Kazushige Ueda, Hiromichi Ohta, Masahiro Hirano, Maiko Kikuchi, Hiroshi Yanagi, Toshio Kamiya, and Hideo Hosono. "Heavy hole doping of epitaxial thin films of a wide gap p-type semiconductor, LaCuOSe, and analysis of the effective mass." American Institite of Physics, 2007. http://hdl.handle.net/2237/11981.
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Amor, Sarrah. "Étude des défauts dans les alliages de semi-conducteurs à grand gap B(AlGa)N et de leur rôle dans les propriétés de transport : application aux photo-détecteurs U." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0286/document.
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Le nitrure de gallium (GaN) et ses alliages ternaires et quaternaires suscitent de plus en plus d’intérêt dans les communautés scientifiques et industrielles pour leur potentiel d’utilisation dans des dispositifs électroniques haute fréquence, dans les transistors à forte mobilité électroniques, dans la photo-détection UV et les cellules solaires de nouvelles générations. L’aboutissement de ces nouveaux composants reste entravé à l’heure actuelle, entre autre, par la non maîtrise des techniques d’établissement de contacts électriques. C’est dans ce cadre général que s’inscrivent les travaux de cette thèse. Même si l’objectif principal de cette thèse concerne l’étude des défauts électriquement actifs dans les alliages de semiconducteurs à grand gap B(AlGa)N et de leur rôle dans les propriétés de transport, la réalisation des contacts ohmiques et des contacts Schottky constitue une étape essentielle dans la réalisation des dispositifs à étudier. Pour les contacts ohmiques, nous avons déposé des couches de type Ti/Al/Ti/Au (15/200/15/200) par évaporation thermique. Des résistances spécifiques des contacts de l’ordre de 3x10-4Wcm2 ont été déterminées par les méthodes des TLM linéaires et confirmées par les TLM circulaires. Une modélisation théorique a été entreprise dans ce sens pour analyser les mesures expérimentales. Ensuite on a réalisé des diodes Schottky en déposant des contacts métalliques de Platine (Pt) d’épaisseur 150 nm. Des facteurs d’idéalité de 1.3 et une hauteur de barrière de 0.76 eV ont été obtenus et d’une manière reproductible. Une fois ces dispositifs réalisés, une étude des mécanismes de transport a été entreprise et nous a permis de mettre en évidence l’existence des effets tunnel direct et assisté par le champ, en plus de l’effet thermoïonique classique. Ceci a été mis en évidence par des mesures de courant et de capacité en fonction de la température. Pour les photodétecteurs, nous avons réalisés les mêmes mesures de courant et de capacité à l’obscurité et sous illumination à des longueurs d’ondes adaptées. Ces mesures nous ont permis de comprendre les phénomènes de gain qu’on a observés sur ces échantillons et aussi de mettre en évidence des mécanismes thermiquement actifs, dont les énergies d’activation ont été déterminées par la technique de l’Arrhenius. L’étude des défauts électriquement actifs a été menée par la technique transitoire de capacité de niveaux profonds, la (DLTS). Cette technique a été récemment mise en oeuvre au laboratoire et nous a permis d’effectuer des mesures sous différentes conditions incluant diverses polarisations de repos, différentes fréquences, et différentes hauteurs et largeurs d’impulsion de polarisation. Un des résultats importants est la possibilité de caractérisation à la fois des pièges à majoritaires et des pièges à minoritaire en changeant simplement les conditions de polarisation et contrairement aux procédures habituelles où une excitation optique supplémentaire est souvent nécessaire pour augmenter la concentration des porteurs minoritaires. Il a ainsi été mis en évidence, en accord avec la plupart des résultats de la littérature, l’existence de 6 pièges à électrons, tous situés en dessous de 0.9 eV de la bande de conduction, de trois pièges à trous dans l’intervalle 0.6 - 0 .7 eV au dessus de la bande de valence et un piège à trous distribué à l’interface. Une procédure rigoureuse de fit a été mise au point et a permis de confirmer nos résultats obtenus par la procédure classique de l’ArrheniusGallium nitride (GaN) and its ternary and quaternary alloys are attracting more and more interest in the scientific and industrial communities for their potential for use in high frequency electronic devices, for transistors with high electronic mobility, for UV photo-detection and new-generation solar cells. The outcome of these new components is still be seen to be limited in many areas, mainly due to the lack of control of electrical contacts implementation techniques. It is in this context that this thesis takes place.Although the main objective of this thesis deals with the study of the electrically active defects in high band gap B(AlGa)N semiconductor alloys and their role in the transport properties, the production of ohmic and Schottky contacts is an essential step in the realization of the devices under study. For the Ohmic contacts, we have deposited Ti/Al/Ti/Au (15/200/15/200) layers by thermal evaporation. Using the Transfer Length Method (TLM), we obtained specific contact resistances in the order of 3x10-4Wcm2. The Circular TLM has also confirmed this result. Besides, a theoretical modelling has been carried out to analyse the experimental measurements. Schottky diodes were then produced by depositing 150 nm platinum (Pt) metal contacts. An ideality factor of 1.3 and a barrier height of 0.76 eV were obtained. On the other hand, a study of transport mechanisms has been performed. It allowed us to demonstrate the existence of the direct tunnelling and the Thermionic Field Emission, in addition to the conventional thermionic effect. This result was underpinned by current and capacity measurements as a function of temperature. For photo detectors, we performed the same measurements of current and capacity in darkness and under illumination at suitable wavelengths. These measurements allowed understanding the internal gain that was observed on the samples. Furthermore, they show the effect of the thermally active mechanisms whose activation energies were determined by the Arrhenius technique. Using the Deep-Level Transient Spectroscopy (DLTS) technique followed up the study of the electrically active defects. This technique has recently been implemented in the laboratory. It allowed us to perform measurements under different conditions including various reverse bias, different frequencies, and different voltage pulse amplitudes and durations. One of the important results is the possibility of characterizing both majority and minority traps by simply changing the polarization conditions, as opposed to the usual procedures where an additional optical excitation is often necessary to increase the concentration of the minority carriers. In accordance with most of the encountered literature results, we found 6 electron traps all located below 0.9 eV of the conduction band, 3 hole traps in the 0.6-0.7 eV range above the valence band and one hole trap distributed at the interface. A rigorous procedure was developed and confirmed our results obtained by the standard Arrhenius technique
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Filsecker, Felipe. "Characterization and evaluation of a 6.5-kV silicon carbide bipolar diode module." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-217848.
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This work presents a 6.5-kV 1-kA SiC bipolar diode module for megawatt-range medium voltage converters. The study comprises a review of SiC devices and bipolar diodes, a description of the die and module technology, device characterization and modelling and benchmark of the device at converter level. The effects of current change rate, temperature variation, and different insulated-gate bipolar transistor (IGBT) modules for the switching cell, as well as parasitic oscillations are discussed. A comparison of the results with a commercial Si diode (6.5 kV and 1.2 kA) is included. The benchmark consists of an estimation of maximum converter output power, maximum switching frequency, losses and efficiency in a three level (3L) neutral point clamped (NPC) voltage-source converter (VSC) operating with SiC and Si diodes. The use of a model predictive control (MPC) algorithm to achieve higher efficiency levels is also discussed. The analysed diode module exhibits a very good performance regarding switching loss reduction, which allows an increase of at least 10 % in the output power of a 6-MVA converter. Alternatively, the switching frequency can be increased by 41 %.
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Ovramenko, Tamara. "STM studies of single organic molecules on silicon carbide." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112315.
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L’interaction de molécules organiques avec les surfaces semiconductrices permet de contrôler les propriétés physiques de ces dernières et ce, soit à travers une modification locale en utilisant des molécules individuelles, soit par la passivation de la surface par une mono-couche complète. Aussi, le contrôle de l’interaction moléculaire nous permet de modifier les propriétés intrinsèques des molécules à travers un découplage électronique partiel ou complet entre les orbitales moléculaires et la surface. Pour atteindre ces objectifs, cette thèse présente l’étude expérimentale de l’adsorption de molécules sur la surface semiconductrice à large gap de 6H-SiC(0001)-3x3. Les expériences ont été réalisées à l’aide d’un microscope à effet tunnel opérant dans les conditions d’Ultra-Haut Vide et de température ambiante (UHV RT-STM). Les résultats ont été comparés à des études théoriques employant des calculs selon la théorie de la fonctionnelle de la densité (DFT). Trois molécules on été étudié durant ce travail de thèse : C60, Caltrope et Trima. Les études STM et DFT montre que les molécules individuelles de C60 sont chimisorbé à la surface de carbure de silicium SiC(0001)-3x3 à travers la formation d’une seule liaison Si-C avec un seul adatome de silicium, contrairement aux autres surfaces semiconductrices où la molécule se chimisorbe en formant plusieurs liaisons. Trois sites d’adsorption par rapport à l’adatome de Si de la maille de surface ont été observés. Pour expliquer les observations STM, les forces de Van der Waals entre la molécule de C60 et les atomes de la surface voisins ont du être pris en compte dans les calculs DFT. Il a été observé aussi que les molécules de C60 forment de petits clusters même à de faibles taux de couverture ce qui indique la présence d’un état précurseur de la molécule et des interactions intermoléculaires non négligeable. La molécule de Caltrope, nouvellement synthétisée, a été étudié aussi bien sur la surface de Silicium que celle de SiC. Le dépôt de cette molécule complexe ne peut être réalisé selon la méthode d’évaporation classique sans induire sa dissociation et a donc nécessité l'emploi de techniques d’évaporation spécifiques. Nos résultats expérimentaux montrent un comportement remarquable: le dépôt de molécule individuelle est induit sur la surface de manière efficace par la pointe du STM démontrant ainsi l’idée d’imprimerie moléculaire. Suite à son adsorption sur la surface de silicium à travers une seule liaison, la molécule de Caltrope se comporte comme un moteur moléculaire activé thermiquement. La troisième molécule a être étudié est la molécule de Trima. Elle a été sélectionnée à cause de sa taille comparable à la distance des ad-atomes de silicium de la surface de SiC. La structure chimique de la molécule qui se termine par un groupement cétone rend possible la fonctionnalisation de la surface. Ceci est révélé par les calculs DFT de la densité de charge. La distribution de charge montre qu’il n’y a pas de partage entre les atomes d’oxygènes de la molécule et les ad-atomes de la surface et donc nous avons un évidence claire pour la formation d’une liaison dativeThe interaction of organic molecules with a semiconductor surface enables the physical properties of the surface to be controlled, from a local modification using individual isolated molecules to passivation using a complete monolayer. Controlling the molecular interaction also allows us to modify the intrinsic properties of the molecules by partial or complete electronic decoupling between the molecular orbitals and the surface. To this end, this thesis presents experimental studies of the adsorption of molecules on the wide band gap 6H-SiC(0001)-3×3 substrate. The experiments were performed using Ultra-High Vacuum Room Temperature Scanning Tunneling Microscopy (UHV RT STM) and the results were compared with comprehensive theoretical Density Functional Theory (DFT) calculations. Three different molecules were studied in this thesis: C60, Caltrop and Trima. The STM and DFT studies show that individual C60 fullerene molecules are chemisorbed on the silicon carbide SiC(0001)-3×3 surface through the formation of a single Si-C bond to one silicon adatom, in contrast to multiple bond formation on other semiconducting surfaces. We observed three stable adsorption sites with respect to the Si adatoms of the surface unit cell. To explain the STM observations, Van der Waals forces between the C60 molecule and the neighboring surface atoms had to be included in the DFT calculations. The C60 molecules are also observed to form small clusters even at low coverage indicating the presence of a mobile molecular precursor state and non negligible intermolecular interactions. The second newly designed Caltrop molecule was studied on both the Si and SiC surfaces. Intact adsorption of this complex organic molecule cannot be realized using classical adsorption methods and requires the use of specific evaporation techniques. Our experimental results show remarkable behavior: The STM tip efficiently deposits single molecules one at a time, demonstrating the concept of single molecule printing. After adsorption on the Si surface through one bond, the Caltrop operates as a thermally activated molecular rotor. The third molecule to be studied is the Trima molecule. This molecule was chosen because it is commensurable in size with the surface Si adatom distance. The chemical termination of the molecule with a ketone group enables the successful functionalization of the SiC surface. The Trima molecule provides a rare and clear-cut example of the formation of two dative bonds between the oxygen atoms of the carbonyl groups and the Si adatoms of the SiC surface. This is revealed by the DFT calculations of the charge density. The charge distribution shows that there is no sharing of electrons between the oxygen atoms of the molecule and the surface which is clear evidence for the formation of a dative bond
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Maertens, Alban. "Etude de la réalisation d'une structure transistor (FET) pour l'observation de l'exciton du ZnO sous champ électrique." Thesis, CentraleSupélec, 2016. http://www.theses.fr/2016SUPL0009/document.
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Ce manuscrit porte sur la conception d’un transistor à effet de champ destiné à l’observation de la photoluminescence de l’exciton et des complexes excitoniques chargés du ZnO sous l’influence d’un champ électrique. Pour cela, des simulations ont permis de définir un cahier des charges de la structure du transistor afin de bloquer la conductivité dans le canal de ZnO et d’appliquer un champ électrique intense. La seconde partie concerne le choix du matériau de grille et de l’électrode transparente de surface pour l’observation de la photoluminescence dans le canal. L’oxyde de gallium (-Ga2O3) a été choisi car il présente un grand gap, des propriétés d’isolant et de semi-conducteur avec dopage. Cependant les films de Ga2O3 dopés avec Ti, Sn, Zn et Mg élaborés par MOCVD n’ont pas révélé de conductivité. Les films d’alliages (Ga,Sn)2O3 n’ont pas non plus montré de conductivité et leur structure est étudiée intensivement. Des traitements plasma radiofréquence sous flux d’argon, d’oxygène ou d’hydrogène ont permis de montrer que l’implantation de l’hydrogène donne lieu à un niveau donneur avec une énergie d’activation de 7 meV. La conductivité est toutefois modulée par le dopage en Sn et les traitements s’accompagnent d’un changement de la sous-stœchiométrie en oxygène qui diminue la transparence à cause de la formation de niveau profond de lacune d’oxygène. La structure finale de la grille transparente dans l’ultraviolet pour l’observation de la photoluminescence du ZnO peut donc être élaborée par une grille diélectrique de -Ga2O3 puis une électrode conductrice transparente de (Ga,Sn)2O3 traitée superficiellement par un plasma d’hydrogèneThis manuscript covers the design of a field transistor for the observation of photoluminescence of the exciton and the charged excitonic complex of ZnO under the influence of an electric field. For this, simulations have helped to define the specifications of the transistor structure to block the conductivity in the ZnO channel and applying a strong electric field. The second part concerns the choice of gate material and the surface transparent electrode for the observation of photoluminescence in the channel. The gallium oxide (-Ga2O3) was chosen because it has a large gap, insulating properties and semiconductor properties with doping. However, Ga2O3 films doped with Ti, Sn, Zn and Mg MOCVD did not show conductivity. Films of alloys (Ga,Sn)2O3 have not shown either conductivity and their structure is studied intensively. Radio frequency plasma treatment under a flux of argon, oxygen or hydrogen have shown that implantation of hydrogen gives rise to a donor level with 7 meV activation energy. However, the conductivity is modulated by doping Sn and treatments are accompanied by a change of sub-stoichiometry in oxygen, which reduces the transparency due to the formation of deep level of oxygen vacancy. The final structure of the transparent gate in the ultraviolet for the observation of photoluminescence of ZnO can be prepared by a dielectric gate -Ga2O3 and a transparent conductive electrode of (Ga,Sn)2O3 surface treated by a plasma of hydrogen
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Chan, Yung. "Optical functions of wide band gap semiconductors /." View the Table of Contents & Abstract, 2004. http://sunzi.lib.hku.hk/hkuto/record/B32021264.
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Tirino, Louis. "Transport Properties of Wide Band Gap Semiconductors." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5210.
Full textAbstract:
Transport Properties of Wide Band Gap Semiconductors
Louis Tirino III
155 pages
Directed by Dr. Kevin F. Brennan
The objective of this research has been the study of the transport properties and breakdown characteristics of wide band gap semiconductor materials and their implications on device performance. Though the wide band gap semiconductors have great potential for a host of device applications, many gaps remain in the collective understanding about their properties, frustrating the evaluation of devices made from these materials.
The model chosen for this study is based on semiclassical transport theory as described by the Boltzmann Transport Equation. The calculations are performed using an ensemble Monte Carlo simulation method. The simulator includes realistic, numerical energy band structures derived from an empirical pseudo-potential method. The carrier-phonon scattering rates and impact ionization transition rates are numerically evaluated from the electronic band structure. Several materials systems are discussed and compared. The temperature-dependent, high-field transport properties of electrons in gallium arsenide, zincblende gallium nitride, and cubic-phase silicon carbide are compared.
Since hole transport is important in certain devices, the simulator is designed to simulate electrons and holes simultaneously. The bipolar simulator is demonstrated in the study of the multiplication region of gallium nitride avalanche photodiodes.
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Cheekoori, Reddiprasad. "Electron transport in wide energy gap semiconductors." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/40421.
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The dependence of the low-field electron drift mobility on the crystal temperature is determined for a number of wide energy gap semiconductors of interest. The materials considered include gallium nitride, aluminium nitride, indium nitride, and zinc oxide; while indium nitride is not a wide energy gap semiconductor in of itself, alloys of indium nitride with gallium nitride are. For the bulk results, it is found that indium nitride exhibits the highest low-field electron drift mobility while aluminium nitride exhibits the lowest low-field electron drift mobility. This is related to the small effective mass of electrons in indium nitride and the large effective mass of electrons in aluminium nitride. For the case of electrons confined within a two-dimensional electron gas, it is found that the low-field electron drift mobility exceeds that corresponding to the bulk material. This is due to the enhanced screening that electron concentrations exceeding the bulk ionized impurity concentrations level offer, i.e., surplus electrons act to further screen the ionized impurities; in a two-dimensional electron gas, the electron concentrations may far exceed those found in a bulk material. Recommendations for further study are suggested.
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Chan, Yung, and 陳勇. "Optical functions of wide band gap semiconductors." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B45015338.
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Saadatkia, Pooneh. "Optoelectronic Properties of Wide Band Gap Semiconductors." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1562379152593304.
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Mickevičius, Jūras. "Carrier recombination in wide-band-gap nitride semiconductors." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091121_102304-00016.
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The thesis is dedicated to carrier recombination investigations in wide-band-gap semiconductors and their structures. The complex experimental studies were performed by combining several different techniques. Carrier dynamics in GaN epilayers were investigated under extremely low and high excitation conditions. A new method for interpreting photoluminescence decay kinetics was suggested by interrelating luminescence and light-induced grating decay transients. The new approach for studies of yellow band in GaN was shown by linking the carrier lifetime with yellow band intensity. Two AlGaN epilayers grown by different novel growth techniques were compared and the factors limiting carrier lifetime were identified. Moreover, more evidence on alloy mixing and band potential fluctuations in AlGaN was provided by our study. Essential knowledge was attained about carrier dynamics in high-Al-content AlGaN/AlGaN multiple quantum well structures: the influence of built-in electric field and carrier localization on carrier dynamics. Most of the samples under study were grown by MEMOCVDTM growth technique, and our study confirmed the high potential of this innovative growth technique for improving material quality.Disertacija skirta krūvininkų rekombinacijos tyrimams plačiatarpiuose nitridiniuose puslaidininkiuose bei jų dariniuose. Kompleksiniai eksperimentiniai tyrimai buvo atlikti naudojant kelias skirtingas metodikas. Atlikti krūvininkų dinamikos GaN sluoksniuose tyrimai labai žemų ir aukštų sužadinimų sąlygomis. Pasiūlytas naujas liuminescencijos gesimo kinetikų interpretavimo metodas, siejant liuminescencijos ir šviesa indukuotų dinaminių gardelių kinetikas. Naujas požiūris į geltonosios liuminescencijos juostą GaN sluoksniuose leido susieti geltonosios liuminescencijos intensyvumą su krūvininkų gyvavimo trukme. Skirtingomis technologijomis augintų AlGaN sluoksnių palyginimas suteikė informacijos apie juostos potencialo fliuktuacijas bei krūvininkų gyvavimo trukmę ribojančius veiksnius AlGaN medžiagose. Atskleista naujų krūvininkų dinamikos daugialakštėse AlGaN/AlGaN kvantinėse duobėse ypatumų – vidinio elektrinio lauko bei kvantinės duobės pločio fliuktuacijų sąlygotos lokalizacijos įtaka krūvininkų dinamikai. Dauguma tirtų bandinių buvo auginti naudojant MEMOCVDTM technologiją ir tyrimai patvirtino šios technologijos potencialą siekiant pagerinti medžiagų kokybę.
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Kusch, Gunnar. "Characterization of low conductivity wide band gap semiconductors." Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27392.
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This thesis covers research on low electric conductivity wide band gap semiconductors of the group-III nitride material system. The work presented focussed on using multi-mode scanning electron microscope (SEM) techniques to investigate the luminescence properties and their correlation with surface effects, doping concentration and structure of semiconductor structures. The measurement techniques combined cathodoluminescence (CL) for the characterization of luminescence properties, secondary electron (SE) imaging for imaging of the morphology and wavelength dispersive X-ray (WDX) spectroscopy for compositional analysis. The high spatial resolution of CL and SE-imaging allowed for the investigation of nanometer sized features, whilst environmental SEM allowed the characterisation of low conductivity samples. The investigated AlxGa₁₋xN samples showed a strong dependence on the miscut of the substrate, which was proven to influence the surface morphology and the compositional homogeneity. Studying the influence of the AlxGa₁₋xN sample thickness displayed a reduced strain in the samples with increasing thickness as well as an increasing crystalline quality. The analysis of AlxGa₁₋xN:Si samples showed the incorporation properties of Si in AlxGa₁₋xN, the correlation between defect luminescence, Si concentration and resistivity as well as the influence of threading dislocations on the luminescence properties and incorporation of point defects. The characterization of UV-LED structures demonstrated that a change in the band structure is one of the main reasons for a decreasing output power in AlₓGa₁₋ₓN based UV-LEDs. In addition the dependence of the luminescence properties and crystalline quality of InxAl₁₋xN based UV-LEDs on various growth parameters (e.g. growth temperature, quantum well thickness) was investigated. The study of nanorods revealed the influence of the template on the compositional homogeneity and luminescence of InxAl₁₋xN nanorod LEDs. Furthermore,the influence of optical modes in these structures was studied and found to provide an additional engineering parameter for the design of nanorod LEDs.
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Zhang, Shaolin. "Wide band gap nanomaterials and their applications." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B41758225.
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Bump, Buddy J. "Synthesis and Characterization of CdSe/ZnS Core/Shell Quantum Dot Sensitized PCPDTBT-P3HT:PCBM Organic Photovoltaics." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1309.
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Durable, cheap, and lightweight polymer based solar cells are needed, if simply to meet the demand for decentralized electrical power production in traditionally “off-grid” areas. Using a blend of Poly(3-hexylthiophene-2,5-diyl) (P3HT), Phenyl-C61-butyric acid methyl ester (PCBM), and the low band-gap polymer Poly[2,6-(4,4-bis-(2- ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), we have fabricated devices with a wide spectral response and 3% power conversion efficiency in AM 1.5 conditions; however, this thin film system exhibits only 0.43 optical density at 500 nm. To improve the performance of this polymer blend photovoltaic, we aim to increase absorption by adding CdSe(ZnS) core (shell) quantum dots. Four groups of devices are fabricated: a control group with an active polymer layer of 16 mg/mL P3HT, 16 mg/mL PCBM, and 4 mg/mL PCPDTBT; and three groups with dispersed quantum dots at 4 mg/ml, 1 mg/mL, and 0.25 mg/mL. The (CdSe)ZnS quantum dots are coated with octadecylamine ligands and have a peak absorbance at 560 nm and peak emission at 577 nm. The active layer was dissolved in chlorobenzene solvent and spun on glass substrates, patterned with indium tin oxide. The devices were then annealed for fifteen minutes at 110° C, 140° C, and 170° C. Current-voltage characteristic curves v and optical density data were taken before and after the anneal step. Finally, surface characterization was conducted with atomic force microscopy and electrostatic force microscopy. When compared to the control, the sensitized devices exhibited increased absorption and depressed electrical performance with increasing quantum dot loading. The surface morphology, both electrical and physical, showed deviation from the typical values and patterns shown by the control that increased with quantum dot loading. When the degrading electrical characteristics, increasing optical absorbance, and surface changes, are considered together, it becomes likely that the quantum dots interact in a significant manner with the morphology of the P3HT phase, which leads to an overall decrease in performance.
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Bolger, Jeremy Adam. "Picosecond nonlinear optical processes in wide-gap semiconductors andpolydiacetylene." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/1500.
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Harrison, Daniel. "Impact ionisation rate calculations in wide band gap semiconductors." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4651/.
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Calculations of band-to-band impact ionisation rates performed in the semi-classical Fermi’s Golden Rule approximation are presented here for the semiconductors GaAs, In(_0.53)Ga(_0.47)As and Si(_0.5)Ge(_0.5) at 300K. The crystal band structure is calculated using the empirical pseudopotential method. To increase the speed with which band structure data at arbitrary k-vectors can be obtained, an interpolation scheme has been developed. Energies are quadratically interpolated on adapted meshes designed to ensure accuracy is uniform throughout the Brillouin zone, and pseudowavefunctions are quadratically interpolated on a regular mesh. Matrix elements are calculated from the pseudowavefunctions, and include the terms commonly neglected in calculations for narrow band gap materials and an isotropic approximation to the full wavevector and frequency dependent dielectric function. The numerical integration of the rate over all distinct energy and wavevector conserving transitions is performed using two different algorithms. Results from each are compared and found to be in good agreement, indicating that the algorithms are reliable. The rates for electrons and holes in each material are calculated as functions of the k-vector of the impacting carriers, and found to be highly anisotropic. Average rates for impacting carriers at a given energy are calculated and fitted to Keldysh-type expressions with higher than quadratic dependence of the rate on energy above threshold being obtained in all cases. The average rates calculated here are compared to results obtained by other workers, with reasonable agreement being obtained for GaAs, and poorer agreement obtained for InGaAs and SiGe. Possible reasons for the disagreement are investigated. The impact ionisation thresholds are examined and k-space and energy distributions of generated carriers are determined. The role of threshold anisotropy, variation in the matrix elements and the shape of the bands in determining characteristics of the rate, particularly the softness of the rate's threshold behaviour are investigated.
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Zhang, Shaolin, and 張少林. "Wide band gap nanomaterials and their applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B41758225.
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Chen, Xinyi, and 陈辛夷. "Wide band-gap nanostructure based devices." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B49799290.
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Wide band gap based nanostructures have being attracting much research interest because of their promise for application in optoelectronic devices. Among those wide band gap semiconductors, gallium nitride (GaN) and zinc oxide (ZnO) are the most commonly studied and optoelectronic devices based on GaN and ZnO have been widely investigated. This thesis concentrates on the growth, optical and electrical properties of GaN and ZnO nanostructures, plus their application in solar cells and light emitting diodes (LEDs).
GaN-nanowire based dye sensitized solar cells were studied. Different post-growth treatments such as annealing and coating with a TiOx shell were applied to enhance dye absorption. It was found that TiOx increased the dye absorption and the performance of the dye sensitized solar cell.
ZnO nanorods were synthesized by vapor deposition and electrodeposition. Post-growth treatments such as annealing and hydrothermal processing were used to modify the defect chemistry and optical properties. LEDs based on GaN/ZnO heterojunctions were studied. The influence of ZnO seed layers on GaN/ZnO LEDs was investigated. GaN/ZnO LEDs based on ZnO nanorods with MgO and TiOx shells were also prepared in order to modify the LED performance. The coating condition of the shell was found to influence the current-voltage (I-V) characteristics and device performance. Moreover, high brightness LEDs based on GaN with InGaN multiple quantum wells were also fabricated.
The origin of the emission from GaN/ZnO LEDs was studied using different kinds of GaN substrates. Direct metal contacts on bare GaN substrates were also employed to investigate the optical emission and electrical properties. It is found that the emission from the GaN/ZnO LEDs probably originated from the GaN substrate.
GaN/ZnO LEDs with MgO as an interlayer were also fabricated. The MgO layer was expected to modify the band alignment between the GaN and the ZnO. It was shown that GaN/MgO/ZnO heterojunctions (using both ZnO nanorods and ZnO films) have quite different emission performance under forward bias compared to those that have no MgO interlayer. An emission peak was around 400 nm could originate from ZnO.
Nitrogen doped ZnO nanorods on n-type GaN have been prepared by
electrodeposition. Zinc nitrate and zinc acetate were used as ZnO precursors and NH4NO3 was used as a nitrogen precursor. Only the ZnO nanorods made using zinc nitrate showed obvious evidence of doping and coherent I-V characteristics. Cerium doped ZnO based LEDs were fabricated and showed an emission that depended on the cerium precursor that was employed. This indicates that the choice of precursor influences the growth, the materials properties and the optical properties of ZnO.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
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Blewett, Ian James. "Ultrafast nonlinear optical processes in wide-gap II-VI semiconductors." Thesis, Heriot-Watt University, 1996. http://hdl.handle.net/10399/754.
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Kahn, Kevin. "Two-dimensional wide band gap semiconductors for deep UV photonics." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/48013.
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Light emitters and detectors in the deep ultraviolet range (DUV) are of great current interest, with applications in water purification, solar-blind photodetectors and communication, biohazard detection, and phosphor-assisted white light emitters. However, DUV optoelectronics based on solid-state heterostructures suffer from low internal and external quantum efficiencies, due to issues relating to their fundamental material properties. These limitations motivate the exploration of new classes of materials for these applications. The recent emergence of two-dimensional (2D) materials has opened up new possibilities in this area, however 2D materials also bring new experimental challenges: particularly the deposition and characterisation of atomic layers, as well as scientific challenges, especially understanding how interactions between the 2D layer and the substrates and/or the environment may affect the properties of the 2D layer. In this thesis, the optical properties of promising materials for deep UV photonics are assessed using a combination of techniques, and the mathematical links between the resulting data are demonstrated. The first part of this work discusses the optical and structural properties of gallium nitride and its alloys, which are the foundation of current optoelectronics, and addresses the optical processes of freestanding and supported 2D hexagonal boron nitride (h-BN) as a potential candidate for high-efficiency deep UV optoelectronic devices. The objectives are to (i) confirm the validity of the models on well-known materials, (ii) determine whether h-BN is a good candidate for deep UV optoelectronics and (iii) whether and how interactions between 2D h-BN with substrates must be taken into consideration. The second part discusses the optical properties of barium zirconate titanate with changes in composition and dimensionality. The objectives are (i) to apply models developed for the nitrides to extract the bulk properties of these oxides, and (ii) to determine whether they are good candidates for deep UV optoelectronics in their 2D form.
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Yellai, Kashyap Williams John R. "Post ion-implantation surface planarization process for 4H-SiC wafers using carbon encapsulation technique." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Fall/Theses/YELLAI_KASHYAP_13.pdf.
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Hamad, Hassan. "Détermination des coefficients d'ionisation de matériaux à grand gap par génération multi-photonique." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0017/document.
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L’utilisation des semi-conducteurs à large bande interdite (wide bandgap ou WBG) tels que le carbure de silicium SiC, le nitrure de gallium GaN, le diamant, etc… s’est répandue dans le domaine de l’électronique de puissance ces dernières décennies. Leurs caractéristiques électroniques et mécaniques font des WBGs des solutions alternatives pour remplacer le traditionnel silicium. Cependant, des études supplémentaires sont indispensables pour améliorer la tenue en tension, les pertes statiques et dynamiques et les performances en fonctionnement à haute température des composants WBGs. Dans ce cadre, deux bancs expérimentaux OBIC (Optical Beam Induced Current) spécifiques « en cours de développement » sont mis en place pendant cette thèse. L’OBIC consiste à éclairer avec un faisceau laser de longueur d’onde appropriée une jonction polarisée en inverse, des porteurs de charge sont alors créés par absorption photonique. On peut alors mesurer un courant induit par faisceau optique (OBIC) lorsque les porteurs sont générés dans la zone de charge d’espace. Après une première phase de préparation et d’adaptation de l’environnement expérimental, des essais ont mené à la démonstration du principe de génération multi-photonique en éclairant une jonction SiC avec un faisceau vert (532 nm). L’analyse des différentes mesures OBIC nous a permis de construire une image du champ électrique à la surface de la diode : une analyse non destructive pour étudier l’efficacité des protections périphériques des jonctions et pour détecter les défauts dans la structure cristalline. Egalement, la durée de vie des porteurs minoritaires a été déduite par l’analyse de la décroissance du courant OBIC au bord de la jonction. Les coefficients d’ionisation sont également déterminés par la méthode OBIC, ces coefficients sont des paramètres clés pour la prévision de la tension de claquage des composants. Nous avons réalisé des mesures OBIC dans le GaN, et nous avons observé un effet d’absorption bi-photonique dans le diamant avec un faisceau UV (349 nm)In the last few decades, the use of wide bandgap (WBG) semiconductors (silicon carbide SiC, gallium nitride GaN, diamond, etc…) has become popular in the domain of power electronics. Their electronic and mechanical characteristics made of the WBGs a good alternative to the traditional silicon. However, additional studies are mandatory to improve the breakdown voltage, static and dynamic losses, and the performance at high temperature of the WBG devices. In this context, two specific experimental benches OBIC (Optical Beam Induced Current) -under development- are set up during this thesis. OBIC method consists to generate free charge carriers in a reverse biased junction by illuminating the device with an appropriate wavelength. An OBIC signal is measured if the charge carriers are generated in the space charge region. After a first phase of preparation and adaptation of the experimental environment, OBIC measurements led to demonstrate the multi-photonic generation by illuminating a SiC junction with a green laser (532 nm). OBIC measurements allowed giving an image of the electric field at the surface of the diode: OBIC presents a non-destructive analysis to study the efficiency of the peripheral protection and to detect the defects in the semi-conductor. Minority carrier lifetime was also deduced by studying the OBIC decrease at the edge of the space charge region. Ionization rates were extracted using OBIC method; these coefficients are key parameters to predict the breakdown voltage of the devices. OBIC measurements were also realized on the GaN, and two-photon generation was highlighted by measuring an OBIC current in the diamond when illuminating it with a UV laser beam (349 nm)
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Chen, Jian. "Calculation of linear and nonlinear optical susceptibilities in wide gap semiconductors /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487941504293146.
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Robutel, Rémi. "Etude des composants passifs pour l'électronique de puissance à "haute température" : application au filtre CEM d'entrée." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00665819.
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Les travaux présentés dans ce manuscrit sont dédiés à l'étude des composants passifs pour l'électronique de puissance à haute température. Des condensateurs et des matériaux magnétiques sont sélectionnés et caractérisés jusqu'à environ 250°C. Les caractéristiques électriques et électromagnétiques montrent, pour certains de ces composants et matériaux, des dépendances significatives en fonction de la température, mais également des non-linéarités et des phénomènes d'hystérésis. Les caractérisations sont ensuite exploitées pour la conception d'un filtre CEM d'entrée d'un onduleur de tension de 2kW. Une démarche et des considérations liées au dimensionnement d'un filtre sont détaillées. Un démonstrateur de filtre CEM est testé en charge et à haute température (200°C). Les résultats montrent une dépendance relativement faible des perturbations conduites entre 150kHz et 30MHz en fonction de la température (environ +6dBµA entre 25°C et 200°C selon la norme DO-160F). Le fonctionnement à haute température de composants passifs au sein d'un filtre CEM pour l'électronique de puissance a été démontré. En complément du filtre à composant discret et pour répondre aux besoins d'atténuation à haute fréquence qui seront accrus pour les convertisseurs à base de semi-conducteurs à grand gap (SiC et GaN) qui commutent plus rapidement que des interrupteurs de type IGBT en Si, nous avons proposé l'intégration de condensateurs de mode commun au sein d'un module de puissance. Les résultats simulés et expérimentaux ont montré une réduction des perturbations conduites grâce à l'intégration de ces condensateurs. Cette solution, compatible avec un fonctionnement à haute température, est positionnée comme une solution alternative à un filtre d'entrée complexe (multi-niveaux) et s'inscrit dans la tendance actuelle des IPEM (Intelligent/Integrated Power Electronics Module) qui recherche l'intégration de fonctions dans le module de puissance. L'ensemble de ces travaux souligne par ailleurs l'importance du packaging pour l'électronique de puissance à haute température.
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Lim, Sang-Hyun. "Characterization of p-type wide band gap transparent oxide for heterojunction devices." Amherst, Mass. : University of Massachusetts Amherst, 2009. http://scholarworks.umass.edu/dissertations/AAI3359903/.
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