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1
Haasmann, Daniel Erwin. "Active Defects in 4H–SiC MOS Devices". Thesis, Griffith University, 2015. http://hdl.handle.net/10072/367037.
Testo completoAbstract (sommario):
The research findings presented in this thesis have provided several key contributions towards a better understanding of the SiC–SiO2 interface in SiC MOS structures. The electrically active defects directly responsible for degrading the channel-carrier mobility in 4H–SiC MOSFETs have been identified and a novel technique to detect these defects in 4H–SiC MOS capacitors has been proposed and experimentally demonstrated. With a better understanding of defects at the SiC–SiO2 interface two alternative gate oxide growth processes have been proposed to overcome the practical limitations associated with current NO-nitridation techniques in high-volume, production based oxidation furnaces. This work therefore contributes to the wider research effort towards improving the performance of SiC MOSFETs in several ways. The following paragraphs summarise the key conclusions that have been obtained as a result of this study.
Electrically Active Defects and the Channel-Carrier Mobility (Chapter 3)
A critical review of defects at the SiC–SiO2 interface exposed a few key discrepancies in both the current understanding of the dominant defects responsible for channel-carrier mobility degradation in 4H–SiC MOSFETs and in the current approach to characterise and evaluate the SiC–SiO2 interface. Firstly, it was recognised that the Shockley-Read-Hall statistical model, based on thermally activated transport for traps spatially located at the semiconductor-oxide interface, cannot be directly applied to describe the transfer mechanism between free conduction band electrons and the shallow NITs near EC. This implication tends to suggest that the NITs near EC in SiC MOS structures cannot be accurately examined using traditional MOS characterisation techniques that are based on this statistical model. Secondly, in accordance with the studies conducted by Saks et. al. [1-3], it was realized that channel-carrier mobility degradation in 4H–SiC MOSFETs is primarily due to the significantly reduced free electron density in the inversion channel. In light of this understanding, the interfacial defects that actively trap channel electrons under strong inversion conditions were considered to be dominant in these devices as opposed to the NITs near EC that are typically examined using conventional MOS characterisation techniques on N-type MOS capacitors in depletion. To further support this hypothesis, a theoretical analysis of the inversion carrier concentration using the charge sheet model was conducted to demonstrate that the NITs with energy levels corresponding to strong inversion are of key importance to the channel-carrier mobility.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
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2
Almrabet, Meftah M. "Electrically active defects in novel Group IV semiconductors". Thesis, Sheffield Hallam University, 2006. http://shura.shu.ac.uk/19253/.
Testo completoAbstract (sommario):
This thesis presents the electrical characterisation of defects in novel group IV semiconducting materials: semiconducting diamond and silicon germanium (SiGe) virtual substrates. Several methods to clean diamond surfaces are introduced, which lead to the fabrication of a diamond Schottky diode with acceptable characteristics. Current-Voltage (I-V) and Capacitance-Voltage (C-V) measurements were carried out to study the electrical properties of both the diamond and SiGe Schottky diodes. Deep level transient spectroscopy (DLTS) and Laplace DLTS were then carried out to investigate the deep electronic states in these devices. Scanning Electron Microscopy (SEM) was also used to investigate defects in the diamond samples. For the diamond Schottky diodes, I-V and C-V measurements confirmed the quality of the fabricated Schottky diode; the measured phase angle between capacitance and voltage was close to 90° for temperatures greater than 300K and frequencies above 200 kHz and the device clearly exhibited rectification. DLTS and LDLTS measurements of the diamond did not show any signatures that could be attributed to isolated point defects. This could be due to the fact that it was necessary to take the samples to higher temperatures in order to fully ionize the boron in the sample. The boron acceptor is at 0.37 eV above the valence band and therefore only about 5% is ionised at room temperature. During the major part of the study at Manchester, there was no access to a high temperature cryostat. However, a clear capacitance transient was observed at lower temperatures and it is proposed that this is due to emission of holes from boron. Deep traps will be located deeper in the band gap than the boron. An additional problem was that the sample was of polycrystalline structure and is full of grain boundaries, which appear to be implicated in the leakage currents present in our devices. I-V, C-V, DLTS and LDLTS were also used to investigate the deep states in the SiGe virtual substrate. I-V and C-V measurements showed that the SiGe Schottky diode showed some leakage (reported by the suppliers) but nevertheless the diode exhibited rectification. Analysis of the DLTS data showed the presence of a defect in the SiGe samples which could be a structural defect, probably dislocation-related. However, the low background doping meant that a considerable depth below the surface was being measured in DLTS and depth profiling was not possible.
3
Doolittle, William Alan. "Fundamental understanding, characterization, passivation and gettering of electrically active defects in silicon". Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/15710.
Testo completo
4
He, Weiwei. "IGBT series connection based on cascade active voltage control with temporary clamp". Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708196.
Testo completo
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Maës, Clément. "Plasmonique active pour l’infrarouge sur semi-conducteur fortement dopé". Thesis, Montpellier, 2020. http://www.theses.fr/2020MONTS033.
Testo completoAbstract (sommario):
Le contexte de ma thèse se situe dans le cadre de l’imagerie multispectrale infrarouge (IR) et traite notamment de la plasmonique, domaine de l’optique électromagnétique dont le but est d’étudier et d’exploiter des ondes de surface existant à l’interface entre un métal et un diélectrique. On cherche à miniaturiser des fonctions optiques grâce aux nanotechnologies et plus précisément à réaliser du filtrage spectrale IR au niveau du pixel de détection en intégrant un nano-résonateur. Usuellement, on utilise des diélectriques et des métaux mais l’intégration est complexe. J’explore le potentiel offert par les semi-conducteurs fortement dopés pour remplacer les métaux, ce qui pourrait permettre une meilleure intégration aux procédés technologiques de fabrication de photodétecteur ou d’émetteur. J’utilise des semi-conducteurs III-V, compatibles avec la croissance épitaxiale du super-réseau de type 2 (T2SL) des photodétecteurs infrarouge à ondes longues (LWIR). De plus, travailler avec un semi-conducteur fortement dopé offre la possibilité de modifier la fréquence de résonance en ajustant la densité de porteurs libres par action d’une différence de potentiel. J’étudie des architectures de composants "GMR" (Guided-mode resonance), usuellement formées d’un guide d’onde en diélectrique, siège de la résonance, et d’un réseau en diélectrique ou en métal permettant le couplage entre l’onde incidente ou transmise et le mode guidé grâce aux ordres ±1 diffractés par le réseau dans la couche mince. La tendance actuelle est d’intégrer ces composants directement au niveau du pixel de détection mais au prix de nombreuses étapes de fabrication. J’étudie la possibilité d’utiliser exclusivement des semi-conducteurs pour simplifier le procédé de fabrication et permettre une intégration monolithique du filtre au détecteur. Le guide d’onde est constitué d’un semi-conducteur intrinsèque et le réseau en semi-conducteur fortement dopé. La gamme spectrale d’intérêt se situe dans l’infrarouge lointain (8 μm - 14 μm).Dans un premier temps, les démonstrations théorique et expérimentale d’un filtre spectral nanostructuré tout semi-conducteur pour l’infrarouge fondé sur la résonance de mode guidé ont été effectuées. J’ai dimensionné puis fabriqué un échantillon dont la première étape consiste en le dépôt par épitaxie d’une couche de GaSb et d’une couche de InAsSb fortement dopé sur un substrat en GaAs avant une étape de photolithographie pour définir le masque de la gravure ionique réactive afin d’obtenir le réseau de diffraction. Un travail expérimental a ensuite permis de caractériser le composant (mesure sous incidence normale, étude angulaire, mesure à basse température) avec notamment la réalisation d’un banc de caractérisation angulaire. En parallèle, j’ai étudié un empilement approprié de matériaux dopés permettant, par application d’une tension électrique, de déplacer les électrons libres issus du dopage dans le réseau et le guide, ce qui modifie alors localement l’indice de réfraction et donc directement les conditions de guidage de la lumière par variation de phase. Différentes approches ont été présentées pour tenter d’ajuster la longueur d’onde de résonance du filtre spectral GMR : accumulation et déplétion des charges dans le réseau de diffraction, insertion d’une jonction P-N dans le guide d’onde, ...Enfin, une première brique pour l’intégration d’un T2SL dans un nano-résonateur optique pour réaliser un photodétecteur nanostructuré tout semi-conducteur a été étudiée. J’ai proposé́ la conception théorique de plusieurs nano-résonateurs intégrant un photodétecteur de type T2SL (filière InAs/GaSb). J’ai conçu trois architectures aux propriétés spectrales distinctes et qui diffèrent notamment par l’épaisseur de la couche de T2SLThe context of my thesis deals with infrared (IR) multispectral imaging and in particular with plasmonics, a field of electromagnetic optics whose the aim is to study and exploit surface waves existing at the interface between a metal and a dielectric. We seek to miniaturize optical functions thanks to nanotechnologies and more precisely to perform IR spectral filtering at the detection pixel level by integrating a nano-resonator. Usually we use dielectrics and metals, but the integration is complex. I am exploring the potential offered by heavily doped semiconductors to replace metals, which could allow better integration into technological processes for fabricate a photodetector or emitter. I use III-V semiconductors, compatible with the epitaxial growth of type 2 superlattice (T2SL) of long wave infrared photodetectors (LWIR). Furthermore, working with a heavily doped semiconductor offers the possibility of modifying the resonance frequency by adjusting the density of free carriers by the action of a potential difference.I study architectures of "GMR" components (Guided-Mode Resonance), usually formed by a waveguide in dielectric, where occurs the resonance, and a grating in dielectric or metal allowing the coupling between the incident or transmitted wave and the guided mode thanks to the ±1 orders diffracted by the grating in the thin layer. The current trend is to integrate these components directly at the level of the detection pixel but at the cost of numerous fabrication steps. I am studying the possibility of using exclusively semiconductors to simplify the fabrication process and allow monolithic integration of the filter into the detector. The waveguide consists of an intrinsic semiconductor and the grating of heavily doped semiconductor. The spectral range of interest is in the far infrared (8 μm - 14 μm).First, theoretical and experimental demonstrations of an all-semiconductor nano-structured spectral filter for infrared based on guided-mode resonance were carried out. I dimensioned and then fabricated a sample where the first step consists in depositing by epitaxy a layer of GaSb and a layer of highly doped InAsSb on a GaAs substrate before a photolithography step to define the mask of the etching reactive ionic etching in order to obtain the diffraction grating. An experimental work then made it possible to characterize the component (measurement under normal incidence, angular study, measurement at low temperature) with in particular the realization of an angular characterization setup.In parallel, I studied an appropriate stack of doped materials allowing, by applying an electrical voltage, to move the free electrons from doping in the grating and the guide, which then locally modifies the refractive index and therefore directly the conditions for guiding the light by phase variation. Different approaches have been presented in an attempt to adjust the resonance wavelength of the GMR spectral filter: accumulation and depletion of charges in the diffraction grating, insertion of a PN junction in the waveguide, ...Finally, a first brick for the integration of a T2SL in an optical nano-resonator to make an all-semiconductor nano-structured photodetector was studied. I proposed the theoretical design of several nano-resonators integrating a T2SL type photodetector (InAs/GaSb). I designed three architectures with distinct spectral properties, which differ in particular in the thickness of the T2SL layer
6
Hill, Bradford K. Greene Michael E. "A linear CMOS tunable active resistor". Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SPRING/Electrical_and_Computer_Engineering/Thesis/Hill_Bradford_35.pdf.
Testo completo
7
Wang, Lei [Verfasser]. "Small molecule organic semiconductors as efficient visible light-active photocatalysts / Lei Wang". Mainz : Universitätsbibliothek der Johannes Gutenberg-Universität Mainz, 2017. http://d-nb.info/1225685842/34.
Testo completo
8
Toffanin, Stefano. "Multifunctional organic semiconductors as active materials for electronic and opto-electronic devices". Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426094.
Testo completoAbstract (sommario):
Since the first discovery of the photoelectric effect in anthracene, organic compounds have been studied as multi-functional materials because of their capability of showing a variety of properties such as charge transport, light absorption/emission, photoconductivity, electroluminescence and superconductivity.
The work presented in this Ph.D. thesis aims at studying different classes of ?-conjugated organic materials that present functional properties suitable for the realization of opto-electronic devices. In particular we focus our attention on the two specific properties that are deeply correlated to the molecular arrangement in the realization of nano-scale multifunctional devices: charge transport and light emission.
In the technologically appealing thin-films, the molecular arrangement is extremely sensitive to the deposition procedures and to the nature of the substrate. Thus, of great interest is the understanding at the micro- and nano-scale of the molecular architecture and morphological features which favour charge transport and/or energy transfer, in order to enhance performances of opto-electronic devices based on thin films. We show that in general linear ?-oligothiophenes can organize advantageously in thin-films in so as to guarantee the proper overlap between molecular orbitals which enables efficient field-effect charge transport. Introducing a new class of branched oligothiophenes (namely spider-like oligothiophenes) we aim at studying how complex 3D molecular architecture can affect optical emission, supermolecular organization and charge transport properties.
Investigation on the enhancement of light emission efficiency of organic molecular systems is then carried out presenting a new host-guest lasing system obtained by co-evaporation of an oligo(9,9-diarylfluorene) derivative (T3, donor) with a well-known red-emitter dye (DCM, acceptor). In this binary blend, an efficient Förster energy transfer takes place from the T3 matrix to the dye molecules when the dye concentration is properly optimized. Moreover the mirrorless lasing measurements reveal that amplified spontaneous emission threshold of the 2% DCM:T3 sample is almost an order of magnitude lower than the 2% DCM:Alq3 model system measured in the same experimental conditions.
The possibility of combining different functionalities in a single device is of great relevance for the further development of organic electronics in integrated components and circuitry. Organic light-emitting transistors (OLETs) have been demonstrated to be able to combine in a single device the electrical switching functionality of a field-effect transistor and the capability of light generation. When organic materials are implemented as active layers in device realization, interfaces formed by different materials are intrinsically important. The comprehension of the physics behind each interface is a crucial point to design new materials for device applications or to improve the performances of the existing ones
Here we present a new approach for realizing ambipolar light-emitting transistor. In the heterostructure we propose the first layer and third layers are optimized for field-effect charge (electrons and holes) transport. The second layer is formed by a host-guest matrix with high optical performance and showing amplified spontaneous emission under optical pumping.
The specificity of the presented tri-layer based OLET is the intrinsic separation of the charge transport region from the exciton formation region thus preventing completely the exciton-carrier quenching.
The optimization of the charge transport and light emission properties allows the realization of a tri-layer heterojunction presenting balanced electron and hole mobility (~10-1-10-2 cm2/Vs), high charge carrier density in correspondence of the maximum electroluminescence emission (~ 1 KA/cm2) and intense light generation.Fin dalla scoperta dell’effetto fotoelettrico nell’antracene, i composti organici sono stati studiati come materiali multifunzionali data la loro capacità di mostrare una varietà di proprietà differenti, come il trasporto di carica, emissione/assorbimento di luce, fotoconduttività, elettroluminescenza e superconduttività. Il lavoro presentato in questa tesi di dottorato si prefigge lo scopo di studiare differenti classi di materiali organici ? coniugati che presentino le proprietà funzionali adatte per la realizzazione di dispositivi optoelettronici. In particolare viene prestata particolare attenzione allo studio di due specifiche proprietà che sono profondamente connesse con l’organizzazione molecolare nei dispositivi multifunzionali con dimensioni nanometriche: il trasporto di carica e l’emissione di luce. Nei film sottili, univocamente considerati interessanti dal punto di vista tecnologico, l’organizzazione molecolare è fortemente dipendente dai processi di deposizione e dalla natura del substrato. Per aumentare le prestazioni dei dispositivi basati sui film sottili risulta fondamentale comprendere le strutture supermolecolari e le caratteristiche morfologiche su scala micro- e nanometrica che possono favorire il trasporto di carica e/o i processi di trasferimento di energia. Si dimostra che in generale gli oligotiofeni lineari depositati in film sottile possano organizzarsi vantaggiosamente in modo da garantire l’opportuna sovrapposizione tra gli orbitali molecolari che permette un efficiente trasporto di carica. Introducendo una nuova classe di oligotiofeni ramificati, denominati spider-like, ci proponiamo di studiare come una complessa architettura 3D possa modificare le proprietà di emissione, di organizzazione supermolecolare e di trasporto. Si procede quindi ad indagare la possibilità di aumentare l’efficienza di emissione di luce di sistemi organici molecolari mediante l’introduzione di un nuovo sistema host-guest con proprietà di lasing ottenuto sublimando un derivato diarilfluorenico (T3, donore) con una noto colorante emettitore nel rosso (DCM, accettare). In questa soluzione solida binaria, si verifica un efficiente trasferimento di energia alla Förster tra la matrice di T3 e le molecole di colorante quando la concentrazione di colorante viene opportunamente ottimizzata. Inoltre, la soglia di emissione spontanea amplificata del campione avente le molecole di DCM disperse al 2% in peso nel T3 risulta quasi un ordine di grandezza più bassa rispetto a quella del campione modello misurato nelle stesse condizioni sperimentali avente la stessa concentrazione in peso si molecole di DCM disperse in una matrice di Alq3. La possibilità di combinare diverse proprietà funzionali in un unico dispositivo risulta di notevole interesse per un ulteriore sviluppo dell’elettronica organica nei componenti integrati e nei circuiti. Si è dimostrato che i transistor organici ad emissione di luce sono capaci di combinare in un singolo dispositivo le proprietà di switch dei transistor ad effetto di campo con la capacità di generare luce. Quando i materiali organici vengono utilizzati come strati attivi nei dispositivi, le interfacce formate dai diversi materiali assumono un ruolo di primaria importanza. La comprensione dei processi fisici che avvengono ad ogni interfaccia è cruciale per disegnare nuovi materiali per dispositivi o per aumentare le prestazioni quelli già esistenti. In questo lavoro di tesi viene presentato un nuovo approccio per realizzare transistor ambipolari ad emissione di luce. Nell’eterogiunzione che viene proposta il primo e il terzo strato sono dedicati al trasporto di portatori di carica (elettroni e lacune) per effetto di campo mentre il secondo strato è formato da una soluzione solida host-guest che mostra efficiente emissione di luce ed emissione spontanea di luce se pompata otticamente. La specificità dell’approccio che presentiamo è che le regioni di trasporto di carica sono fisicamente separate da quella in cui avviene la formazione dell’eccitone. In questo modo viene ridotta completamente l’interazione tra l’eccitone e il portatore di carica. Dopo aver ottimizzato il trasporto di carica e le proprietà di emissione di luce, si è potuto realizzare un dispositivo basato sull’eterogiunzione a tre strati che presenta valori di mobilità per gli elettroni e le lacune bilanciati (~10-1-10-2 cm2/Vs), alta densità di portatori di carica in corrispondenza del massimo di elettroluminescenza (~ 1 KA/cm2) e intensa emissione di luce.
9
Palakodety, Atmaram Mohanty Saraju. "CMOS active pixel sensors for digital cameras current state-of-the-art /". [Denton, Tex.] : University of North Texas, 2007. http://digital.library.unt.edu/permalink/meta-dc-3631.
Testo completo
10
Shen, Chao. "Study of CMOS active pixel image sensor on SOI/SOS substrate /". View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202003%20SHEN.
Testo completoAbstract (sommario):
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 67-69). Also available in electronic version. Access restricted to campus users.
11
Lowry, Curtis Wayne. "Optical nonlinearities in passive and active gallium arsenide with applications to optical switching and laser instabilities". Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186295.
Testo completoAbstract (sommario):
Nonlinear optical properties of passive and active semiconductors are investigated experimentally and theoretically. Improvement of switching cycle time in optical nonlinear etalons to 40 ps is demonstrated, and strained-layer InGaAs/GaAs quantum well material is used in an asymmetric etalon to greatly improve switching power and contrast. Coherent energy transfer (CET) induced by injection of an external light field is demonstrated in a GaAs quantum well vertical-cavity surface-emitting laser (VCSEL). The evolution of CET induced asymmetric gain with increasing injected power is investigated experimentally and theoretically, and it is found that the CET induced effective gain peak and dip are detuned proportionally with injected power as in homogeneously broadened media and in contrast to other multi-wave effects in GaAs which are detuned proportionally with the light field. Transfer of gain modification between orthogonally polarized modes of the VCSEL and cascading of gain modification within a mode is observed and investigated. The approach of a laser to an injection locked state through increased injected power is investigated experimentally and theoretically, showing new emission frequencies produced which evolve to chaos-like behavior before reaching the phase locked state. CET induced gain modification is used to demonstrate low-power high-contrast switching between polarization modes of the VCSEL with differential gain of 3,510. Switching speed and switching bistability is observed and investigated. Injection induced modification of VCSEL transverse modes is studied experimentally and theoretically. Field defects in the resulting field are observed, and their locations are dependent on the frequency of the injected field, in contrast to the temporally evolving defects normally observed. The rich behavior of nonlinear properties, especially in gain media provide interesting results and valuable applications.
12
Gibson, Jr Allen. "Design and simulation of CMOS active mixers". Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4765.
Testo completoAbstract (sommario):
This paper introduces a component of the Radio Frequency transceiver called the mixer. The mixer is a critical component in the RF systems, because of its ability for frequency conversion. This passage focuses on the design analysis and simulation of multiple topologies for the active down-conversion mixer. This mixer is characterized by its important design properties which consist of conversion gain, linearity, noise figure, and port isolation. The topologies that are given in this passage range from the most commonly known mixer design, to implemented design techniques that are used to increase the mixers important design properties as the demand of CMOS technology and the overall RF system rises. All mixer topologies were designed and simulated using TSMC 0.18 micrometer] CMOS technology in Advanced Design Systems, a simulator used specifically for RF designs.ID: 030646192; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.E.E.)--University of Central Florida, 2011.; Includes bibliographical references.
M.S.E.E.
Masters
Electrical Engineering and Computing
Engineering and Computer Science
Electrical Engineering
13
McGarvey, Brian Scott. "Coupling of solid-state and electromagnetic equations for the computationally efficient time-domain modeling and design of wireless packaged geometries with nonlinear/active devices". Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-04092007-055514/.
Testo completoAbstract (sommario):
Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2007.Tentzeris, Manos, Committee Chair ; Laskar, Joy, Committee Member ; Papapolymerou, John, Committee Member.
14
Mitchell, Lee. "Investigation of Selected Optically-Active Nanosystems Fashioned using Ion Implantation". Thesis, University of North Texas, 2006. https://digital.library.unt.edu/ark:/67531/metadc5259/.
Testo completoAbstract (sommario):
Opto-electronic semiconductor technology continues to grow at an accelerated pace, as the industry seeks to perfect devices such as light emitting diodes for purposes of optical processing and communication. A strive for greater efficiency with shrinking device dimensions, continually pushes the technology from both a design and materials aspect. Nanosystems such a quantum dots, also face new material engineering challenges as they enter the realm of quantum mechanics, with each system and material having markedly different electronic properties. Traditionally, the semiconductor industry has focused on materials such Group II-VI and III-V compounds as the basis material for future opto-electronic needs. Unfortunately, these material systems can be expensive and have difficulties integrating into current Si-based technology. The industry is reluctant to leave silicon due in part to silicon's high quality oxide, and the enormous amount of research invested into silicon based circuit fabrication. Although recently materials such as GaN are starting to dominate the electro-optical industry since a Si-based substitute has not been found. The purpose of the dissertation was to examine several promising systems that could be easily integrated into current Si-based technology and also be produced using simple inexpensive fabrication techniques such ion implantation. The development of optically active nano-sized precipitates in silica to form the active layer of an opto-electronic device was achieved with ion implantation and thermal annealing. Three material systems were investigated. These systems consisted of carbon, silicon and metal silicide based nanocrystals. The physical morphology and electronic properties were monitored using a variety of material characterization techniques. Rutherford backscattering/channeling were used to monitor elemental concentrations, photoluminescence was used to monitor the opto-electronic properties and transmission electron microscopy was used to study the intricate morphology of individual precipitates. The electronic properties and the morphology were studied as a function of implant dose, anneal times and anneal temperatures.
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Palakodety, Atmaram. "CMOS Active Pixel Sensors for Digital Cameras: Current State-of-the-Art". Thesis, University of North Texas, 2007. https://digital.library.unt.edu/ark:/67531/metadc3631/.
Testo completoAbstract (sommario):
Image sensors play a vital role in many image sensing and capture applications. Among the various types of image sensors, complementary metal oxide semiconductor (CMOS) based active pixel sensors (APS), which are characterized by reduced pixel size, give fast readouts and reduced noise. APS are used in many applications such as mobile cameras, digital cameras, Webcams, and many consumer, commercial and scientific applications. With these developments and applications, CMOS APS designs are challenging the old and mature technology of charged couple device (CCD) sensors. With the continuous improvements of APS architecture, pixel designs, along with the development of nanometer CMOS fabrications technologies, APS are optimized for optical sensing. In addition, APS offers very low-power and low-voltage operations and is suitable for monolithic integration, thus allowing manufacturers to integrate more functionality on the array and building low-cost camera-on-a-chip. In this thesis, I explore the current state-of-the-art of CMOS APS by examining various types of APS. I show design and simulation results of one of the most commonly used APS in consumer applications, i.e. photodiode based APS. We also present an approach for technology scaling of the devices in photodiode APS to present CMOS technologies. Finally, I present the most modern CMOS APS technologies by reviewing different design models. The design of the photodiode APS is implemented using commercial CAD tools.
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Lo, Keng Wai. "Wideband active-balun variable-gain low-noise amplifier for mobile-TV applications". Thesis, University of Macau, 2010. http://umaclib3.umac.mo/record=b2148237.
Testo completo
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Monti, Federico. "Time sampling using four-wave mixing to measure the dynamics of semiconductor nanolasers". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP026.
Testo completoAbstract (sommario):
Les nanolasers PhC suscitent de plus en plus d'attention en raison de leur capacité unique à manipuler et à confiner la lumière à une très petite échelle. Leur empreinte réduite et leur seuil bas en font des candidats idéaux pour la réalisation de connexions optiques, répondant ainsi à la demande croissante en matière de vitesse de transmission des données et de consommation d'énergie. De plus, leur géométrie singulière permet de contrôler leurs propriétés d'émission spontanée. Cela révèle l'unicité des nanolasers PhC d'un point de vue fondamental, soulignant leur potentiel à servir de sujets de recherche novateurs dans l'interaction lumière-matière. Malgré ces avantages, une caractérisation de leur émission et de leurs propriétés dynamiques fait toujours défaut, en raison des limitations actuelles des capacités de détection aux longueurs d'onde infrarouges.Dans cette thèse, j'ai développé une technique de détection à porte temporelle basée sur FWM, pour mesurer la réponse ultra-rapide des nanolasers 1D. En étudiant attentivement l'interaction entre les non-linéarités et la dispersion, il a été possible d'atteindre une sensibilité élevée de quelques photons et une résolution de 2 ps. Des améliorations supplémentaires de la sensibilité, jusqu'à moins d'une détection de photon, sont prévues en utilisant des puissances de pompe plus élevées. Cela peut ouvrir la voie à l'étude des statistiques des photons et des effets quantiques au cœur du régime quantique.Les profils des nanolasers 1D présentent un début très rapide de l'émission et une décroissance longue, compatible avec un facteur β de 0,12 et une durée de vie du photon de 20 ps. Une nouvelle approche pour obtenir les valeurs de ces deux paramètres contrôlant la dynamique du laser a été développée : elles ont été directement extraites de la réponse ultra-rapide des nanolasers, au lieu de se baser uniquement sur des mesures à l'état stationnaire telles que la courbe S, qui, dans de nombreux cas, peuvent conduire à des estimations inexactes en raison de l'interdépendance de ces paramètres. La réponse dynamique des nanolasers 1D est compatible avec une vitesse maximale de modulation d'environ 30 GHz, répondant à l'exigence de sources laser ultra-compactes à faible seuil pour les circuits intégrés photoniques et les communications optiques.La haute sensibilité et résolution de la technique nous ont permis de mesurer, pour la première fois à notre connaissance, une conversion de longueur d'onde adiabatique de photons avec un décalage de longueur d'onde aussi important que 1,2 nm. Cela montre le potentiel de la technique dans l'étude des dynamiques ultra-rapides aux longueurs d'onde NIRPhC nanolasers are receiving more and more attention due to their unique capacity to manipulate and confine light at a very small scale. Their small footprint and low thresholds make them ideal candidates for realizing optical interconnects, thus addressing the increasing demands for data transmission speed and power consumption. Moreover, their singular geometry enables the control of their spontaneous emission properties. This reveals PhC nanolasers' uniqueness from a fundamental point of view, highlighting their potential to serve as candidates for novel research in light-matter interaction. Despite these advantages, a characterization of their emission and their dynamical properties is still missing, due to the current limitations of the detection capabilities at infrared wavelengths.In this thesis, I have developed a time gating detection technique based on FWM, to measure the ultra fast response of 1D nanolasers. By carefully studying the interplay between nonlinearities and dispersion, it was possible to reach a high sensitivity of a few photons and a resolution of 2 ps. Further improvements in sensitivity, down to less than a photon detection, is predicted by employing higher gate powers. This can open the way to study photon statistics and quantum effects deep in the quantum regime.The profiles of 1D nanolasers feature a very fast onset of the emission and a long decay, compatible with a β factor of 0.12 and a photon lifetime of 20 ps. A novel approach to obtaining the values of these two parameters controlling laser dynamics has been developed: they have been directly retrieved from the%The manner in which these two parameters controlling laser dynamics have been obtained constitutes a novel approach, as they have been directly retrieved from theultra-fast response of nanolasers, instead of solely relying on steady state measurements such as the S curve, which, in many cases, can lead to inaccurate estimations due to the interdependence of these parameters. The dynamical response of 1D nanolasers is compatible with a maximum modulation speed of around 30 GHz, fullfiling the requirement for low threshold ultra compact laser sources for photonic integrated circuits and optical communications.The high sensitivity and resolution of the technique allowed us to measure for the first time, to the best of our knowledge, an adiabatic wavelength conversion of photons with a wavelength shift as large as 1.2 nm. This shows the potential of the technique in studying ultra fast dynamics at NIR wavelengths
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Christofferson, James. "Thermal microscopy of active semiconductor devices /". Diss., Digital Dissertations Database. Restricted to UC campuses, 2004. http://uclibs.org/PID/11984.
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Pande, Peyush. "Characterization of Active Defects in SiC MOSFETs". Thesis, Griffith University, 2020. http://hdl.handle.net/10072/394315.
Testo completoAbstract (sommario):
In the recent years, SiC has become a popular material for power semiconductor devices, after decades long dominance of Si. SiC metal‒oxide‒semiconductor field-effect transistors (MOSFETs) are now commercially available and performing beyond the theoretical limits of Si MOSFETs, however, they are still far from the theoretical limits of SiC. One of the major issues in the commercial SiC MOSFETs is the low channel-carrier mobility, which is attributed to the high density of defects at or near the SiC/SiO2 interface. Consequently, it is necessary to characterize the SiC/SiO2 interface appropriately for the future development of SiC power devices.
This thesis begins with a critical review of conventional characterization techniques for SiC metal‒oxide‒semiconductor (MOS) devices, which are directly adapted from techniques developed for Si. To address the challenges in characterizing SiC/SiO2 interface, a new characterization technique is proposed, which measures the effect of near-interface traps (NITs) in the strong-accumulation region of N-type SiC MOS capacitors. The technique measures the current through a SiC MOS capacitor in strong-accumulation and compares it to the trap-free current. With this technique, an active defect with energy levels localized between 0.13 eV to 0.23 eV, above the bottom of conduction band, is identified. As the effect of NITs is observed only at high frequencies, it is expected to be located very close to the SiC/SiO2 interface. To further investigate the effect of high temperature and positive bias stress on the identified NITs, the MOS capacitors are measured at high temperatures with positive bias stress. No significant difference is observed between measurements performed before and after high temperature bias stress. This led to the conclusion that the temperature independent tunneling is responsible for the trapping and de-trapping of channel electrons to and from the NITs. For the first time in this work we have demonstrated the NITs with response time in tens of ns. A detailed explanation of trapping/de-trapping mechanism of NITs, localized in energy, is also presented in this thesis. The developed technique is further used to perform a comparative analysis of NITs in as-grown and nitrided gate oxides. The density of NITs in nitrided gate oxide is localized in energy whereas it tends to decrease with increasing energy levels in as-grown gate oxide. It is experimentally shown that the nitridation helps to eliminate NITs further away from the SiC/SiO2 interface.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Full Text
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Neophytou, Ares Ioanni. "Hybrid active optical switching using semiconductor laser devices". Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260354.
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Bauer, Stefan. "Nonlinear dynamics of semiconductor lasers with active optical feedback". Doctoral thesis, [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973616423.
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Pitcher, P. G. "Distribution of electrically active centres in boron implanted cadmium mercury telluride". Thesis, University of Surrey, 1986. http://epubs.surrey.ac.uk/847907/.
Testo completoAbstract (sommario):
The objective of this work was to investigate the distribution of donor-like centres produced by boron implantation into p-type, Bridgeman grown Hg[0.8]Cd[0.2]Te and fabricate photodiodes from implanted substrates. Low carrier concentration substrates, 4-5x10[16]cm[-3], were implanted at room temperature with dose rates (&phis;) of 4x10[-2] or 6x10[-3]muAcm[-2], to a total dose of 1 x 10[15]B[+] cm[-2] (50,100keV) or 1x10[14]B[+]cm[-2] (150keV), respectively. Encapsulated specimens were annealed at 200°C or 235°C to activate the dopant or redistribute electrically active radiation damage centres to produce p-n junctions. The effects of materials processing on Hg[l-x]Cd[x]Te was investigated by x-ray photoelectron spectroscopy. Concentration profiles of electrically active centres were obtained from differential measurements of the Hall effect and resistivity at 77K. Through a comparison of distributions in as-implanted and annealed samples, the nature of donor-like centres forming the distributions were established. The quality of photodiodes produced from identical samples was assessed through current-voltage, capacitance-voltage and optoelectronic measurements. The nature and distribution of donor-like centres are dependent upon the dose rate of boron ions. An immobile defect is contained within the implanted region. Mercury interstitials (Hg[int]) are complexed within the implanted region for &phis; > 4x10[-2] muAcm[-2]. Irradiation enhanced diffusion of Hg[int] occurs if &phis; < 6x10[-3] muAcm[-2]. Thermal annealing redistributes bound and unbound accompanied by recombination with mercury vacancies and the formation of electrically neutral complexes. Annealing at 235°C for 10 mins completely removes the donor-like activity ascribed to Hg's [int] and reduces the concentration of electrically active immobile defects. P-N junctions are formed between the mercury vacancy distribution and unbound Hg's[int] or the immobile damage centres in annealed substrates. Junction formation is inhibited by the formation of the bound Hg[int] complex. Optimum R[o]A[j] products may be obtained from junctions formed from the immobile defect centre, although degradation of the implanted region occurs after annealing at 235°C. Anodic oxides grow by the differential electromigration of ions, which can produce a passivating layer to further anodization. The native oxide on Hg[0.8] Cd[0.2] Te is an ill-defined chemical mixture of the primary elements (Cd, Hg, Te). Native oxides degrade the R[o]A product of p-n junctions.
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Liddell, W. J. "Polarisation and spectral characteristics of spontaneous emission in active optical waveguides". Thesis, University of Bath, 1986. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376271.
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Hamamoto, Kiichi. "Active multi-mode-interferometer laser diodes and semiconductor optical amplifiers /". Zürich, 2000. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13822.
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Schwaiger, Stephan [Verfasser]. "Rolled-Up Metamaterials Containing Active Semiconductor Quantum Structures / Stephan Schwaiger". München : Verlag Dr. Hut, 2012. http://d-nb.info/1028786441/34.
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Motamedi, Ali Reza. "Ultrafast nonlinear optical properties of passive and active semiconductor devices". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66017.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references.
Nonlinear optical properties and ultrafast carrier dynamics of slab-coupled optical waveguide amplifiers, silicon nanowaveguides, and III-V semiconductor saturable Bragg reflectors are studied. The limits imposed by two photon absorption and free-carrier absorption on the gain and output powers of an InGaAsP/InP slab-coupled optical waveguide amplifier with a confinement factor of [gamma] = 0.5% are determined. The two-photon absorption coefficient and the induced freecarrier absorption cross-section were measured to be 65cm/GW and 7x10-4 cm2, respectively. The effects of two-photon absorption begin to limit the gain significantly for pulses shorter than 40ps. The carrier recovery times were observed to vary between 390 to 160ps for 1A to 4A bias currents, and the short-pulse saturation fluence of the gain was determined to be 1.4mJ/cm2. Furthermore, nonlinear optical processes in high-index-contrast waveguide circuits consisting of 106nm x 497nm silicon waveguides with Si0 2 and HSQ cladding layers were studied using a heterodyne pump probe experimental setup. The linear loss of the waveguides was determined to be 6.5dB/cm. The two-photon absorption coefficient and free-carrier absorption effective crosssection were determined to be 0.68cm/GW, and 1.9x10-17 cm 2, respectively. Coefficients for the index changes due to optical Kerr effect, and free-carrier density were determined to be 3.2x10- 4 cm 2/W, and -5.5x10-21 cm3. Effects of the proton bombardment on linear loss and carrier lifetimes in the devices were also studied. Carrier lifetime reduction to 33ps with a linear loss of only 14.8dB/cm was achieved using a proton bombardment level of 105 /cm 2. Ultrafast dynamics of semiconductor saturable absorber mirrors were also investigated. The addition of resonant layers to the absorbers resulted in lower saturation fluence and increased non-saturable loss. Proton bombardment was utilized on these devices as well, to decrease the carrier recovery times. With proton bombardment of single-absorber layer devices with 40KeV proton energies at a dose of 1015/cm2, a 1.5ps carrier recovery time was achieved in single-absorber structures.
by Ali Reza Motamedi.
Ph.D.
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Hildmann, Julia [Verfasser]. "Nuclear Spin Phenomena in Optically Active Semiconductor Quantum Dots / Julia Hildmann". Konstanz : Bibliothek der Universität Konstanz, 2014. http://d-nb.info/1049393600/34.
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Milovanovic, Mihailo. "A study of active mode-locking of external cavity semiconductor lasers". Thesis, University College London (University of London), 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261067.
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Lämmlin, Matthias. "GaAs-based semiconductor optical amplifiers with quantum dots as an active medium". [S.l.] : [s.n.], 2006. http://opus.kobv.de/tuberlin/volltexte/2007/1476.
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Bach, Susan Elizabeth. "Chirp compensation in active mode-locked semiconductor diode laser using a DFB". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36504.
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Hsu, Kevin. "Stochastic mode-locking theory and short pulse generation by active mode-locking of external-cavity semiconductor lasers". Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/14990.
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Greig, Thomas Alexander. "Development of CMOS active pixel sensors". Thesis, Brunel University, 2008. http://bura.brunel.ac.uk/handle/2438/5345.
Testo completoAbstract (sommario):
This thesis describes an investigation into the suitability of complementary metal oxide semiconductor (CMOS) active pixel sensor (APS) devices for scientific imaging applications. CMOS APS offer a number of advantages over the established charge-coupled device (CCD) technology, primarily in the areas of low power consumption, high-speed parallel readout and random (X-Y) addressing, increased system integration and improved radiation hardness. The investigation used a range of newly designed Test Structures in conjunction with a range of custom developed test equipment to characterise device performance. Initial experimental work highlighted the significant non-linearity in the charge conversion gain (responsivity) and found the read noise to be limited by the kTC component due to resetting of the pixel capacitance. The major experimental study investigated the contribution to dark signal due to hot-carrier injection effects from the in-pixel transistors during read-out and highlighted the importance of the contribution at low signal levels. The quantum efficiency (QE) and cross-talk were also investigated and found to be limited by the pixel fill factor and shallow depletion depth of the photodiode. The work has highlighted the need to design devices to explore the effects of individual components rather than stand-alone imaging devices and indicated further developments are required for APS technology to compete with the CCD for high-end scientific imaging applications. The main areas requiring development are in achieving backside illuminated, deep depletion devices with low dark signal and low noise sampling techniques.
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Chang, J. T. "Active mode-locking of semiconductor lasers and study of optical amplification in diode lasers". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/46995.
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Malape, Maibi Aaron. "Low temperature growth of Amorphous Silicon thin film". Thesis, University of the Western Cape, 2007. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_7768_1254727160.
Testo completoAbstract (sommario):
The growth of amorphous hydrogenated silicon (a-Si:H) thin films deposided by hot wire chemical vapor deposition (HWCVD) has been studied. The films have been characterised for optical and structural properties by means of UV/VIS,FITR,ERDA, XRD.XTEM and Raman spectroscopy. Low subtrate heater temperatures in the range form 130 to 200 degrees celcius were used in this thesis because it is believed to allow for the deposition of device quality a-Si:H which can be used for electronic photovoltaic devices. Furthermore, low temperatures allows the deposition of a-Si:H on any subtrate and thus offers the possibility of making large area devices on flexible organic substances. We showed that the optical and structural properties of grown a-Si:H films depended critically upon whether the films were produced with silane gas or silane diluted with hydrogen gas. We also showed that it is possible to to deposit crystalline materials at low temperature under high hydrogen dilution ratio of silane gas.
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Akram, Nadeem. "Photonic devices with MQW active material and waveguide gratings : modelling and characterisation". Doctoral thesis, KTH, Mikroelektronik och Informationsteknik, IMIT, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-433.
Testo completoAbstract (sommario):
The research work presented in this thesis deals with modelling, design and characterisation of passive and active optical waveguide devices. The rst part of the thesis is related to algorithm development and numerical modelling of planar optical waveguides and gratings using the Method of Lines (MoL). The basic three-point central-di erence approximation of the δ2=δx2 operator used in the Helmholtz equation is extended to a new ve-point and seven-point approximation with appropriate interface conditions for the TE and TM elds. Di erent structures such as a high-contrast waveguide and a TM surface plasmon mode waveguide are simulated, and improved numerical accuracy for calculating the optical mode and propagation constant is demonstrated. A new fast and stable non-paraxial bi-directional beam propagation method, called Cascading and Doubling algorithm, is derived to model deep gratings with many periods. This algorithm is applied to model a quasi-guided multi-layer anti-resonant reecting optical waveguide (ARROW) grating polarizing structure. In the second part of the thesis, our focus is on active optical devices such as vertical-cavity and edge-emitting lasers. With a view to improve the bandwidth of directly modulated laser, an InGaAsP quantum well with InGaAlAs barrier is studied due to its favorable band o set for hole injection as well as for electron con nement. Quantum wells with di erent barrier bandgap are grown and direct carrier transport measurements are done using time and wavelength resolved photoluminescence upconversion. Semi-insulating regrown Fabry-Perot lasers are manufactured and experimentally evaluated for light-current, optical gain, chirp and small-signal performance. It is shown that the lasers having MQW with shallow bandgap InGaAlAs barrier have improved carrier transport properties, better T0, higher di erential gain and lower chirp. For lateral current injection laser scheme, it is shown that a narrow mesa is important for gain uniformity across the active region. High speed directly modulated DBR lasers are evaluated for analog performance and a record high spurious free dynamic range of 103 dB Hz2=3 for frequencies in the range of 1-19 GHz is demonstrated. Large signal transmission experiment is performed at 40 Gb/s and error free transmission for back-to-back and through 1 km standard single mode ber is achieved.QC 20100827
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Jobe, Sean Richard Keali'i. "OPTIMIZATION OF GAN LASER DIODES USING 1D AND 2D OPTICAL SIMULATIONS". DigitalCommons@CalPoly, 2009. https://digitalcommons.calpoly.edu/theses/74.
Testo completoAbstract (sommario):
This paper studies the optical properties of a GaN Laser Diode (LD). Through simulation, the GaN LD is optimized for the best optical confinement factor. It is found that there are optimal thicknesses of each layer in the diode that yield the highest optical confinement factor. There is a strong relationship between the optical confinement factor and lasing threshold—a higher optical confinement factor results in a lower lasing threshold. Increasing optical confinement improves lasing efficiency. Blue LDs are important to the future of lighting sources as they represent the final color in the RGB spectrum that does not have a high efficiency solution. The modeled GaN LD emits blue light at around ~450nm. Each layer of the GaN LD is drawn in a model simulation program called LaserMOD created by RSOFT Design Group, Inc. By properly modifying the properties of each layer, an accurate model of the GaN LD is created and then simulated. This paper describes the steps taken to properly model and optimize the GaN LD in the 1D and 2D models.
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Gilfert, Christian Jürgen [Verfasser]. "High-Speed Semiconductor Lasers based on Low-Dimensional Active Materials for Optical Telecommunication / Christian Jürgen Gilfert". Kassel : Universitätsbibliothek Kassel, 2012. http://d-nb.info/1024364461/34.
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Mashade, Mohamed Bakry el. "Largeur spectrale du laser semiconducteur dans l'approximation d'une couche mince active". Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37607749b.
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Chen, Xiuping. "Embedded active and passive methods to reduce the junction temperature of power and RF electronics". Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51901.
Testo completoAbstract (sommario):
AlGaN/GaN high electron mobility transistors (HEMTs) have been widely used for high power and high frequency RF communications due to their fast switching and large current handling capabilities. The reliability of such devices is strongly affected by the junction temperature where the highest magnitude occurs in a local region on the drain side edge of the gate called the hotspot. Thus, thermal management of these devices remains a major concern in the design and reliability of systems employing AlGaN/GaN HEMTs. Due to the large power densities induced in these devices locally near the drain side edge of the gate, it is clear that moving thermal management solutions closer to the heat generation region is critical in order to reduce the overall junction temperature of the device. In this work, we explore the use of embedded microchannel cooling in the substrate of AlGaN/GaN HEMTs made on Si and SiC substrates and compare them to passive cooling techniques using Si, SiC, and diamond substrates. In addition, the impact of cooling fluids and harsh environmental conditions were considered. The study was performed using a combination of CFD and finite volume analysis on packaged AlGaN/GaN HEMTs. Active cooling using embedded microchannels were shown to have a significant impact on the heat dissipation over the passive cooling methods, approaching or exceeding that of diamond cooled devices. For vertical power devices (IGBT), embedded microchannels in the power electronics substrates were explored. In both the power devices and lateral AlGaN/GaN HEMTs, the use of embedded microchannels with nonlinear channel geometries was shown to be the most effective in terms of reducing the device junction temperature while minimizing the pumping power required.
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Zurletto, Claude. "Influence de recuit à 425o C sur des propriétés électriques du silicium polycristallin : action d'une interface aluminium-silicium". Aix-Marseille 3, 1988. http://www.theses.fr/1988AIX30053.
Testo completoAbstract (sommario):
Analyse des longueurs de diffusion des porteurs minoritaires dans si. Des recuits a 425#oc pendant quelques heures augmentent la longueur de diffusion de 20 a 30 m tant que les valeurs initiales sont inferieures a 60 m. Les effets sont plus marques lorsqu'une couche d'aluminium est prealablement deposee sur la face arriere des echantillons ou lorsque les echantillons sont soumis a une diffusion superficielle de phosphore. Explication des resultats par l'interaction entre atomes d'oxygene dissous, impuretes metalliques, interstitiels de si et defauts (dislocations)
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Moradi, Aali. "Action d'un champ magnétique sur les trions excitoniques dans les puits quantiques de semi-conducteurs". Metz, 2001. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/2001/Moradi.Aali.SMZ0122.pdf.
Testo completoAbstract (sommario):
Le travail présenté dans ce mémoire est consacré à l'étude des excitons chargés (ou trions excitoniques) dans les puits quantiques de semi-conducteurs, en l'absence et en présence d'un champ magnétique. Les résultats numériques ont été particularisé à des composés de type GaAS/GaAlAs et CdTe/CdZnTe en raison des applications potentielles de ces nanostructures dans le domaine de l'optoélectronique. Les excitons chargés résultent de la liaison d'un exciton (paire électron trou) avec un électron (trion négatif) ou un trou (trion positif) et peuvent donc être considérés comme des quasi-particules chargées et mobiles. De ce fait, ils présentent des propriétés originales qui les différencient des autres complexes excitoniques. Dans une première étude, en l'absence de champ magnétique, nous avons déterminé les énergies de liaison de deux types de trions, en nous plaçant dans le cadre de l'approximation de la masse effective et dans un modèle à deux bandes non dégénérées. Pour les composés étudiés, les deux types de trions sont stables pour toutes les valeurs de la largeur des puits. De plus, les raies d'absorption sont très différentes de celle des excitons et des autres complexes excitoniques. Contrairement à ces dernières, elles ne sont pas fines, mais présentent un bord d'absorption principal suivi d'une queue décroissante vers les basses énergies. Nous avons ensuite étudié l'influence d'un champ magnétique perpendiculaire au plan des couches. Il apparaît que le champ conduit à une augmentation des énergies. De plus, pour des champs suffisamment faibles, nous avons montré que les énergies se décomposent en niveaux de Landau, résultant du mouvement du centre de masse chargé dans un plan perpendiculaire au champ. Ce résultat est original, et n'a pas encore lieu à aucune confirmation expérimentale. Enfin, nous avons montré que la magnéto-absorption des trions se réduit en une série de pics de DiracThis work is devoted to the study of the charged excitons (or trions) in semiconductor quantum wells, with or without an external magnetic field. The numerical results concern more particularly GaAS/GaAlAs and CdTe/CdZnTe compounds due to their possible in the field of optoelectronics. Charged excitons result from the binding of an exciton (electron hole pair) and an electron (negative trion) or a hole (positive trion), and may be considered as mobile as charged particles. Thus, they are expected to exhibit original properties, differentiating them from other excitonic complexes. In a first study, without any magnetic field, we have determined the binding energies of the two kinds of trions in the frame of the effective mass approximation within a two isotropic parabolic bands model. It results that in the case of the above compounds, the two kinds of trions are stable against dissociation for all values of the well widths. Moreover the optical absorption does not give rise to sharp lines, as in the cases of excitons or bound excitons, but to a main absorption threshold followed by a decreasing tail on its low energy side. We have also studied the influence of a magnetic field directed along the growth axis. It appears that the field gives rise to an increase of the energies. Moreover in the case of low magnetic fields, we have shown that the energies splits into Landau levels. This is due to the quantized motion of thein-plane motion of the center of mass of the trions. This result is original, and has not yet received experimental confirmation. Finally we have shown that the optical magnetoabsorption reduces to a serie of Dirac peaks
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Feddi, El Mustapha. "Action d'un champ magnétique sur les trions excitoniques dans les semiconducteurs". Metz, 1987. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1987/Feddi.El_Mustapha.SMZ8707.pdf.
Testo completoAbstract (sommario):
Les trions excitoniques sont des quasiparticules chargées et mobiles, pouvant résulter, dans certaines conditions, de la liaison d'un "exciton" avec un électron ou un trou libre dans les semiconducteurs. Ils font partie des états excités électroniques dont l'étude présente un très grand intérêt tant des points de vue pratique que théorique. Elle permet de comprendre les mécanismes des recombinaisons radiatives contrôlant le fonctionnement de certains dispositifs utilisés en optoélectronique. Elle fournit à la physique fondamentale des modèles de systèmes formés de particules ou de quasiparticules couplées, susceptibles d'une analyse expérimentale et théorique très fine. Les trions excitoniques sont susceptibles de donner lieu à des propriétés très originales résultant de leur mobilité et de leur charges. Toutefois, leur existence n'a été établie que dans un nombre limité de semiconducteurs. En effet, leur identification expérimentale est compliquée par le fait que dans les spectres optiques les raies d'excitons, de biexcitons et de trions sont souvent très proches comme le montrent les calculs théoriques des énergies de liaisons. Dans cette étude nous montrons comment l'action d'un champ magnétique permet de distinguer les trions des autres complexes excitoniques. A cet effet, nous déterminons les niveaux d'énergie des trions excitoniques en champ magnétique dans l'approximation de la masse effective. Nous montrons dans quelles conditions le mouvement du centre de masse dans un lan perpendiculaire à la direction du champ donne lieu à l'apparition de niveaux de Landau, analogues à ceux observés pour une particule libre et chargée soumise à un champ magnétique. Nous calculons la contribution à l'énergie totale due mouvement relatif des trois particules en résolvant de façon variationnelle l'équation de Schrödinger. Les résultats obtenus montrent que le champ magnétique stabilise la liaison par suite du rétrécissement des orbitales. Nous déterminons le coefficient d'absorption des transitions dipolaires électriques entre des états d'électrons libres et des états de trions négatifs. Ce dernier présente une série d'oscillations dont les maxima correspondent aux différents niveaux de landau. Enfin nous discutons de l'influence de la température sur les transitions optiques. L'intérêt essentiel de la présente étude est de mettre en évidence, pour la première fois, l'existence de niveaux de Landau et d'un magnétoabsorptionThe excitonic trions are moving bound states of an exciton and an electron or a hole in a semiconductor. Their binding energies are often small as resulting from variational calculations. Though original properties are expected due to their charge, their experimental identification may be difficult because the exciton, biexciton and trion lines are sometimes very close. We show how a constant magnetic field may be used to distinguish the trions from other excitonic complexes. Indeed, in the case of the exciton or biexciton, the motion of the centre of mass may be eliminated by means of a lamb gauge transformation because these complexes are neutral. However, in the case of the charged trions, only the motion in the direction of the field may be eliminated by means of an analog one gauge transformation. Generally speaking, the relative motion cannot be separated from the motion of the centre of mass in a plane perpendicular to the magnetic field. However, for not too high fields, htis latter is expected to be slow in comparison with the former. We therefore separate the two motion in the sense of the Born-Oppenheimer approximation. In this limit, the centre of mass of the trions behave like single charged particles so that additional Landau levels appear in the energy spectrum. Finally, we compute the relative energy by means of the variation method using a 34-term Hylleraas-type wave function and discuss the optical absorption. We show which the absorption coefficient presents a pics succession whose the maxima are in near Landau's levels. Indeed, it show a oscillatory magneto-absorption
43
Feddi, El-Mustapha. "Action d'un champ magnétique sur les trions excitoniques dans les semiconducteurs". Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37604989d.
Testo completo
44
FEDDI, EL MUSTAPHA Stebe Bernard. "ACTION D'UN CHAMP MAGNETIQUE SUR LES TRIONS EXCITONIQUES DANS LES SEMICONDUCTEURS /". [S.l.] : [s.n.], 1987. ftp://ftp.scd.univ-metz.fr/pub/Theses/1987/Feddi.El_Mustapha.SMZ8707.pdf.
Testo completo
45
Fisne, Christophe. "Métasurfaces actives pour applications large bande". Thesis, Toulouse, INPT, 2020. http://www.theses.fr/2020INPT0086.
Testo completoAbstract (sommario):
Les métasurfaces offrent des propriétés électromagnétiques particulières permettant de générer des indices de réfraction inhabituels, produire des bandes électromagnétiques interdites, ou encore créer des surfaces à haute-impédance. Ces dernières, aussi nommées « Artificial Magnetic Conductor (AMC) » sont particulièrement intéressantes dans le domaine antennaire. En effet elles permettent de réduire les couplages de divers éléments rayonnants, mais aussi de miniaturiser les antennes comportant un plan réflecteur. Cependant, leur bande de fonctionnement inférieure à 10%, les rend souvent incompatibles avec des applications large bande. Pour pallier cette limitation en bande passante, l’intégration de circuits actifs de type « non- Foster » ouvre une voie permettant d’élargir la bande passante des surfaces à haute-impédance. Dans ce contexte, l’objectif de la thèse est de concevoir un réflecteur haute impédance largebande grâce à l’intégration de circuits actifs de type « non- Foster ». La bande passante visée est [0,5 GHz ; 1,5 GHz] soit 100% de bande passante relative. Dans cette thèse, une méthodologie de synthèse d’AMC large bande est proposée : un réflecteur AMC sous incidence normale est conçu à partir d’une métasurface connectée à un circuit non-Foster qui est lui-même chargé par une impédance optimisée. Les relations analytiques permettant d’exprimer le coefficient de réflexion de la métasurface en fonction du circuit non-Foster et de sa charge sont explicitées. Dans un premier temps, une métasurface fonctionnant en polarisation rectiligne permettant le report d’un circuit non Foster est proposée. Cette topologie permet de protéger le circuit électronique des ondes électromagnétiques incidentes.De plus, une étude permettant d’étendre le fonctionnement de la métasurface en polarisation circulaire est amorcée. Ensuite, un circuit Non- Foster de type « Negative Impedance Converter (NIC) » est conçu. La topologie du circuit est choisie dans un souci de simplification technologique. La réalisation de ce circuit a été faite en utilisant des composants standards et l’utilisation de potentiomètres permet un contrôle de l’impédance en entrée du circuit. Enfin, la charge de ce circuit NIC est déterminée afin de permettre le comportement AMC large bande en prenant en compte le comportement réel du circuit non FosterMetasurfaces have particular electromagnetic properties such as unusually refractive index, electromagnetic band gap and high impedance surface. Also named Artificial Magnetic Conductor (AMC), they are a focus of interest in the antennas field. Indeed, greater isolation between radiating elements and miniaturization of antenna with reflective plan can be achieved with those structures. Although they suffer from poor bandwidth (less than 10%), which make them inconsistent with wideband applications. To overcome this frequency limitation, implementation of non-Foster active circuits paves the way to extend the bandwidth of high impedance surfaces. In this respect, the thesis goal is to conceive a wideband high-impedance reflector with the integration of non-Foster circuits. The aimed bandwidth is [0.5 GHz; 1.5 GHz], that is to say 100% of the relative bandwidth. In this thesis, a synthesis methodology to realize a wideband AMC is proposed: an AMC reflector under normal incidence is conceived from a metasurface connected to a non-Foster circuit. The circuit is loaded with an optimized impedance. Analytic relationships between the reflection coefficient and the load impedance of the non-Foster circuit are given. Firstly, a metasurface working with linear polarizations and where the connection of the non-Foster circuit is offset. This topology protects the circuit against the perturbations due to the incident electromagnetic waves. Moreover, a study to extend metasurface functioning to circular polarization is under way. Then, a non-Foster circuit of type Negative Impedance Converter (NIC) is designed. A particular topology of circuit is selected in order to simplify the realization. It has been conceived using only components “off-the-shelf” and potentiometers which control the input impedance. Finally, the circuits load is calculated to obtain the attended wideband AMC behavior according with the real performance of the non-Foster circuit
46
Heiser, Thomas. "Developpement d'une technique d'analyse localisee des defauts electriquement actifs dans les semiconducteurs". Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13136.
Testo completoAbstract (sommario):
Methode basee sur l'emission thermique de porteurs electriques pieges par les niveaux profonds dans la bande interdite. La modelisation de la technique a permis de determiner l'influence des divers parametres physiques sur la resolution spatiale de la technique et d'etablir les conditions optimales de mesures. L'exploitation numerisee des signaux augmente sensiblement la capacite de detection de la technique. Le phenomene de "gettering" de l'or par les dislocations ainsi que la diffusion acceleree de l'or a travers le joint de grain d'un bicristal de silicium ont ete mis en evidence
47
Heiser, Thomas. "Développement d'une technique d'analyse localisée des défauts électriquement actifs dans les semiconducteurs". Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37614162c.
Testo completo
48
Marrakchi, Ghanem. "Etude comparative de différentes techniques de recuit rapide sur les défauts électriquement actifs dans l’arséniure de gallium non implante". Lyon, INSA, 1987. http://www.theses.fr/1987ISAL0049.
Testo completoAbstract (sommario):
Nous avons étudié les effets de traitements thermiques rapides sur les propriétés électriques de l'Arséniure de Gallium non implanté. Trois types de recuit sont considérés : le recuit électronique pulsé (REP), le Recuit par Laser Continu (RLC) et le Recuit Rapide Isotherme par lampe (RRI). Nos mesures ont été effectuées sur des dispositifs Schottky formés après traitement thermique. Elles se basent sur l'étude des courbes I(V) : courant-tension et C(V) : capacité-tension pour les caractéristiques électriques, et spectroscopie transitoire de capacité (DLTS) pour l'étude des défauts. Après REP, on assiste à une dégradation d'une couche superficielle du matériau, plus épaisse que la couche ayant subi réellement une transformation de phase (zones fondante et fondue). Ceci entraîne la disparition des défauts natifs EL6, EL3 et EL2 existant dans l'Arséniure de Gallium massif. Par ailleurs, on a observé l'apparition de nouveaux défauts dus au recuit pour les faibles densités d'énergie. Après RLC, des défauts apparaissent dans une couche d'oxyde formée par le traitement sur des couches d'Arséniure de Gallium épitaxiés en phase liquide. Ceci nous a amené, d'une part, à l'étude ·complète expérimentale et théorique d'un continuum de défauts dans la bande interdite, d'autre part, à mettre en évidence un phénomène particulièrement intéressant de relaxation de centres sous champ électrique. Après RRI, tous les défauts natifs présents dans l'Arséniure de Gallium massif disparaissent sauf le piège EL2 qui reste non affecté. Nous avons montré que ce résultat dépend des conditions de recuit, en particulier de la procédure d'encapsulation. Ceci, et le fait que les caractéristiques électriques des échantillons ne changent pas après recuit, nous montrent que le RRI n'introduit pas de couche perturbée comme dans le cas du REP. L'étude comparative des différents types de recuit nous amène à une discussion générale sur la technologie la mieux adaptée au traitement thermique de l'Arséniure de Gallium.
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Azouani, Rabah. "Elaboration de nouveaux nanomatériaux photocatalytiques actifs sous rayonnement visible". Paris 13, 2009. http://www.theses.fr/2009PA132016.
Testo completoAbstract (sommario):
Ce travail de thèse est consacré à la synthèse par méthode sol-gel de nanoparticules de TiO2(précurseur de tétraisopropoxyde de titane) dopées à l’azote de taille contrôlée pour des applications en nanodépôts et en photocatalyse. Les colloïdes métastables sont préparés dans un réacteur à micromélange rapide (turbulent). Des mesures de granulométrie in-situ permettent le suivi de la cinétique de formation des nanoparticules. L’effet du processus de mélange des réactifs sur la distribution de taille a été analysé en utilisant le modèle hydrodynamique k-ε. L’étude de la cinétique de nucléation-croissance a mis en évidence que le modèle de croissance hiérarchique est aussi valable pour les sub-nucleis (clusters). Différents domaines cinétiques de stabilité et de croissance ont été mis en évidence. Les nanoparticules de TiO2 dopées à l’azote ont été préparées par injection d’hydroxyurée (HyU) dans la zone réactionnelle pendant l’étape de nucléation. Le dopage accélère la cinétique des réactions et induit une coloration jaune vif des nanocolloïdes, due à une nouvelle bande d’absorption dans le domaine spectral de 380-550nm. Cela a été expliqué par la formation d’un complexe stable d’ HyU- TiO2, qui lie deux nanoparticules à travers le groupe NCO. Les mesures FTIR, Raman, absorption UV-visible et XPS confirment la formation du complexe. En particulier, les mesures XPS suggèrent la formation de NO interstitiel (pic à 400eV). Les nanodépôts dopés ont été préparés sur des billes de verre, et traités thermiquement afin d'obtenir la phase anatase active photocatalytiquement. Les mesures XPS, ATG-MS et EXAFS montrent que la température de traitement thermique est cruciale pour la rétention de dopant dans les matériaux préparés. Les tests photocatalytiques ont été réalisés sur la dégradation du trichloréthylène en phase gaz sous rayonnement visible. L’influence du taux d’hydrolyse, de la quantité de dopant et de la température de traitement sur l’activité photocatalytique a été étudiéeThis PhD work is devoted to elaboraton of nitrogen-doped TiO2 nanoparticles of controlled size for applications in nanocoatings and photocatalysis. The metastable colloids are prepared in a sol-gel reactor with rapid (turbulent) micro-mixing and in-situ particles granulometry, starting from titanium tétraisopropoxyde precursor. The effect of the fluids mixing on the particle size distribution was analysed using hydrodynamic k-ε modeling. The study of the nucleation-growth kinetics has evidenced that the hierarchical growth mechanism is also valid for the sub-nucleus units (clusters). Different domains of the cluster stability and growth kinetics have been discovered. The nitrogen-doped TiO2 nanoparticles were prepared by hydroxyurea (HyU) injection into the reaction zone at the nucleation stage. The doping accelerates the reaction kinetics and induces strong yellow coloration of the nanocolloid, due to a new absorption band in the spectral range of 380-550 nm. This has been explained by the formation of a stable HyU-TiO2 complex, which bounds two nanoparticles through the NCO group. FTIR, Raman, UV-visible absorption and XPS measurements confirm the complex formation. In particular, the XPS measurements suggest formation of the interstitial NO (400 eV peak). The doped nanocoatings were prepared on glass beads and thereafter were subjected to calcination in order to achieve most catalytically active anatase polymorph. The XPS, ATG-MS and EXAFS measurements indicate that the calcination temperature is critical for the dopant retention in the prepared material. The photocatalytic tests were performed on trichlorethylene degradation in gas phase under visible light illumination. The influence the hydrolysis ratio, HyU molar loading and calcination temperature on photocatalytic activity was studied
50
Remram, Mohamed. "Etude des défauts électriquement actifs induits par le recuit rapide isotherme dans le silicium". Lyon, INSA, 1986. http://www.theses.fr/1986ISAL0028.
Testo completoAbstract (sommario):
Nous avons utilisé la technique de spectroscopie capacitive (DLTS) pour étudier les défauts électriquement actifs introduits par le recuit rapide isotherme (RRI) dans le silicium vierge ou implanté. Aucun niveau piège n'a été détecté dans une structure Schottky Au-Si dopé Phosphore et recuit pendant 5 s, à différentes températures. D'un autre côté, trois niveaux pièges à trous Hl (O,4 eV), H2 (0,29 eV) et H3 (0,31 eV) ont été observés dans le silicium dopé bore (Al-Si(p)) et recuit pendant 5 s entre 850 et 1050°C. Pour les temps de recuit de 10 s et 20h aucun niveau n'a été observé. Les pics de concentration de ces pièges se situent entre 10(exp13) et 10(exp14) cm (exp-3) pour les températures de paliers supérieures ou égales à l000°C. Dans le silicium dopé bore et implanté As+ ou PF5+ ; et recuit RRI, le niveau H3 (0,31 eV) est remplacé par un autre niveau piège à trous H4 (O,4 eV) qui apparaît avec des conditions spécifiques (paramètres RRI, dose et espèce des ions imp1antés). Un seul niveai piège à électrons E(0,6 eV) a été détecté à forte dose d'ions arsenic (0,4(exp15) et 10(exp16) cm(exp-3 ) et à des températures de recuit de 1l00°C pendant 10 s. L'origine des défauts observés, probablement liée aux impuretés métalliques, et la dépendance de la concentration des défauts des paramètres RRI peuvent être expliquées par un modèle faisant appel à deux mécanismes possibles : piégeage en site interstitiel et effet gettering.