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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
471

Thermal And Optical Properties Of Ge-Se Glass Matrix Doped With Te, Bi And Pb

Ganesan, R 01 1900 (has links)
During the last few years the scientific interest in chalcogenides glasses has been provoked on account of their properties and new application possibilities. These materials exhibit electrical and optical properties, which make them useful for several potential applications. Specifically the threshold and memory switching behavior and the infrared transmission of many of these glasses make the materials to be well suitable for use in memory devices and in fiber optics. Multicomponent glasses have been found to be more useful for many of these applications since the properties could be tailored for the specific uses. On account of this there has been great deal of interest in recent years in understanding the composition dependent variations of physical properties in these glasses. Models based on network topology and chemical ordering have been proposed to explain the composition dependence of physical properties. The Chemically Ordered Covalent Network (COCN) model is one of the best efforts put forth in this subject. This model predicts distinctive physical properties of these glasses for compositions at which there is a maximum number of heteropolar bonds. A physical model based on changes in network topology with composition has been proposed recently. This model predicts the rigidity to percolate in the network at the mean coordination number <r> = 2.40. This critical value of <r> at which the rigidity percolates is called the mechanical threshold or the rigidity percolation threshold. One more argument based on medium range interactions, existing in these glassy networks, suggests that the mechanical threshold should occur at <r> = 2.67. A general lack of consensus in the existing experimental reports on the mechanical threshold in some chalcogenides glasses prevents one from identifying the correct threshold value of <r>. A systematic study of the composition dependence of glasses with a large glass-forming region is necessary to resolve this controversy. The correct threshold value of <r> and the reason for the departure from this value in the other cases is the first step towards verifying the applicability of this model to chalcogenide glasses. Glasses belonging to IV — V — VI groups are natural candidates for this study because of their large glass forming region. It also seems possible to isolate the chemical threshold from interfering with the mechanical threshold in some of these glasses. In device applications of any semiconductor the optical and the electrical band gaps need to be varied and this is commonly done by doping. The large density of valence alteration pairs and intrinsic disorder of amorphous semiconductors counter-balances the effects of external additives. As a result, it is hard to electrically dope these materials. Non-equilibrium experimental techniques have been used to some extent, but one of the limitations is that they are confined to the thin film state. The finding that p to n type conduction sign changes can be induced by Bi and Pb in bulk Ge-M (M= S, Se and Te) glasses has therefore created special interest. This thesis deals with Ge-Se glass matrix doped with Te, Bi and Pb. The optical, thermal and electrical properties have been studied. The present thesis work is arranged in several chapters. The basic introduction of chalcogenide glasses is given in chapter one. This includes an introduction to chalcogenide glasses followed by a brief discussion on the important structural models, the possible defects in chalcogenide glasses and the electrical, optical and thermal properties of chalcogenide glasses. The second chapter discusses the experimental techniques used in the present investigations. The basic principles and theory behind the experiments, the experimental setup and the experimental procedure leading to the determination of the physical properties are given here. These include information about Differential Scanning Calorimetry (DSC), Photo acoustic (PA) spectroscopy and Photoluminescence studies. In the third chapter the experimental investigations on Ge-Se-Te glasses are presented. The chapter starts with the preparation and characterization of these glasses. It then gives an account of the earlier studies on Ge-Se-Te glasses that are relevant to the present work. The results of the DSC and PA studies are discussed in the following two sections. In the systems with Gex Se80-x Te20 and Gex Se75.x Te25, glasses with less than 20 at. % of Ge do not show any crystallization peak due to Se rich content. But Te and Ge-rich glasses show strong crystallization tendency. The composition dependence of Tg of this glassy system gives an evidence for the occurrence of the topological threshold or mechanical threshold at <r> = 2.40 and chemical threshold at <r> = 2.67. These can be explained on the basis of COCN model. The optical band gap and thermal diffusivity studies also show anomalous behavior at <r> = 2.40 and <r> = 2.67. The experimental results on Ge-Se-Te glasses are summarized in the last section of this chapter. The investigations on Bi doped Ge-Se and Ge-Se-Te glasses are given in the fourth chapter. The chapter starts with a brief introduction of preparation, characterization and a short review of earlier work. In PA studies the anomalous behavior is observed in thermal diffusivity and thermal diffusion length plot at 8-9 at. % of Bi doping of the Ge-Se and Ge-Se-Te glasses where the conduction changes from p to n type. These results are explained on the basis of percolation model and the formation of Bi2Se3 microcrystalline phase. Finally these results are summarized at the end of the chapter. The fifth chapter is devoted to the investigations on Pb doped Ge-Se glasses. It is arranged in five sections; preparation and characterization, earlier work, Photo acoustic and Photoluminescence studies. In PA studies the composition dependence of thermal diffusivity show anomalous behavior at x =F 9 at % of Pb in Pbx Ge42-x Sesg glasses and y = 21 at. % of Ge in Pb2o Gey Seso-y glasses where the conduction changes from p to n type. After that it reaches the maximum. After the conduction sign changes the conductivity increases with addition of respective Pb and Ge concentration in both series of glasses, which is reflected in thermal diffusivity value also. The results have been explained on the basis of COCN model. From PL studies, the PL intensity is high in un-doped Ge42 Scss glasses. With the addition of Pb into Ge-Se system the PL intensity goes down drastically up to 9 at. % of Pb, beyond 9 at. % the PL intensity is approximately the same up to 15 at. %. In the last section the results are summarized. Chapter six summarizes the essential features of the work reported in the thesis. These conclusions are drawn from the present and the earlier reported studies on Ge-Se-Te glasses, Bi doped Ge-Se and Ge-Se-Te glasses and Pb doped Ge-Se glasses. Finally based on the present experimental results, some future work has been suggested which could throw some light on a better understanding of/? to n transition and defects state of these glasses. It is worth extending the microscopic phase separation studies in these glasses. Highly sensitive experimental techniques are needed in this regard. Also some simulation work like Monte-Carlo simulation and Molecular dynamics simulation needs to be undertaken for understanding the microscopic phase separation and the role of defects in carrier type reversal in these glassy materials. All the references cited in the thesis are collected and listed at the end of the thesis.
472

Molekulare Systeme im Wechselspiel von Struktur und Ladung / Optische in situ Spektroskopie an organischen Dünnschichten

Dienel, Thomas 01 April 2009 (has links) (PDF)
Die optische in situ-Charakterisierung des Aufwachsens organischer Molekülschichten auf isolierenden und metallischen Substraten (Kaliumchlorid, -bromid und Glimmer, beziehungsweise Gold) ist Gegenstand dieser Arbeit. Am Beispiel der Substanzen Perylen-3,4,9,10- tetrakarbonsäuredianhydrid (PTCDA) und Titanylphthalozyanin (TiOPc), die mittels Molekularstrahlepitaxie abgeschieden werden, wird der Einfluss der Anordnung der Moleküle und der gegebenenfalls hinzugefügten Dotierung auf die messbaren Eigenschaften untersucht. Wie wichtig dabei die Feinabstimmung zwischen den Gitterkonstanten des Substrats und der Ausdehnung der Moleküle ist, äußert sich in schmalen Absorptions- und Emissionsbanden im Falle kommensurablenWachstums von PTCDA auf Kaliumchlorid. Diese Anordnung und ihre Metastabilität werden mit begleitenden Rasterkraftmikroskopie-Untersuchungen und Kraftfeldrechnungen nachgewiesen. Ausgehend von Monolagen neutraler Moleküle kann durch die schrittweise Dotierung mit Kalium die spektrale Entwicklung der Absorption von PTCDA-Anionen verfolgt und einzelnen Ladungsstufen – von Mono- bis Tetraanionen – zugeordnet werden. Durch vorherige Bestrahlung mit Elektronen konnte Glimmer so modifiziert werden, dass auch die spektrale Signatur von PTCDA-Monokationen aufgeklärt werden konnte. In Bestätigung früherer Rastertunnelmikoskopie-Ergebnisse zur Ausbildung von TiOPc- Kristallphasen erfolgt das Wachstum von Phase II auf einer Benetzungsschicht, die Phase I-Anordnung aufweist. Die Schichtdickenabhängigkeit der optischen Eigenschaften wird mit einer Genauigkeit im (Sub-)Monolagenbereich bestimmt und der Verlauf von Oszillatorstärke und Emissionslöschung durch die Orientierung der TiOPc-Moleküle zueinander beziehungsweise ihren Abstand zum Substrat erklärt. / The aim of this work is the in situ monitoring of the growth of molecular thin films on either insulating (potassium chloride, -bromide and mica) or gold substrates by optical spectroscopy. The influence of the molecular arrangement and an optionally added doping on the properties is studied on perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA) and titanyl phthalocyanine (TiOPc), deposited by molecular beam epitaxy. The impact of perfect matching between the substrate’s lattice constants and the dimensions of the molecules, appears in narrow absorption and emission bands in case of commensurate growth of PTCDA on potassium chloride. This arrangement and its metastability are proven by accompanying atomic force microscopy and advanced potential energy calculations. Once potassium can be added stepwise to monolayers of neutral PTCDA molecules, the spectral development towards PTCDA anions can be followed and assigned to the reached levels of charging. The crystal growth of TiOPc molecules in phase II takes place on a wetting layer with phase I arrangement, proving earlier results by scanning tunneling microscopy. Measuring the thickness-dependent optical properties with (sub-)monolayer resolution allows a deeper understanding of the dependences of both, the oscillator strength and the efficiency of luminescence quenching, on the molecules’ orientations with respect to each other and on their distance to the substrate.
473

Etude optique de la dynamique des interactions électroniques dans des nanotubes de carbone

Berger, Sébastien 11 December 2007 (has links) (PDF)
Cette thèse est consacrée à l'étude expérimentale des propriétés électroniques des nanotubes de carbone par des techniques de spectroscopie de photoluminescence.<br /> Le travail a d'abord consisté en la préparation et la caractérisation d'échantillons de nanotubes de carbone isolés les uns des autres dans une suspension de surfactant. Ils présentent alors de la luminescence. Intégrés ensuite dans un gel, ils sont adaptés aux températures entre 10 et 300 K. <br /> Le premier volet d'expériences a concerné la spectroscopie de luminescence en régime stationnaire. Les mesures sur des ensembles macroscopiques permettent d'identifier les classes de chiralité présentes et mettent en évidence divers phénomènes de couplage des nanotubes entre eux et à leur environnement. Grâce à un montage de microscopie confocale, on a en outre étudié la luminescence d'un nanotube unique. On s'affranchit ainsi de l'inhomogénéité de l'échantillon, comme le montrent les faibles largeurs de raies (moins de 1 meV à 10 K) et les phénomènes de diffusion spectrale et de clignotement observés à l'échelle de la seconde.<br /> Le second volet d'expériences est consacré à la spectroscopie de photoluminescence résolue en temps à l'échelle picoseconde, sur des ensembles de nanotubes. On mesure la dynamique de recombinaison des excitations élémentaires (excitons), sur 3 ordres de grandeur de variation, dans les chiralités (9,4) et (10,2). L'évolution du temps de vie (300 ps à 10 K, 50 ps à 300 K) et de l'intensité de la luminescence (présentant un maximum à 50 K) donne des informations sur la structure des états excitoniques. On estime en particulier qu'il existe un niveau noir 4 meV en dessous de l'état luminescent.
474

Epitaxies Si/SiGe(C) pour transistors bipolaires avancés

Brossard, Florence 14 May 2007 (has links) (PDF)
L'objectif de cette thèse est d'étudier les épitaxies SiGeC sélectives par rapport au nitrure de silicium afin d'améliorer les performances en fréquence des transistors bipolaires à hétérojonction à structure complètement auto alignée. Pour répondre à cette attente, le système SiH4/GeH4/SiH3CH3/HCl/B2H6/H2 est utilisé pour élaborer nos épitaxies sélectives.<br />Cette chimie à base de silane permet d'augmenter significativement la vitesse de croissance par rapport au système SiCl2H2/GeH4/HCl/H2 utilisé classiquement, aussi bien pour un dépôt silicium sélectif que pour un film SiGe sélectif. Par exemple, pour un film Si0,75Ge0,25 la vitesse de croissance est multipliée par un facteur 8.<br />L'incorporation des atomes de carbone dans les sites substitutionnels est facilitée par cette hausse du taux de croissance. En effet, la teneur en carbone substitutionnel est plus élevée en utilisant le silane comme précurseur de silicium (jusqu'à un facteur 4). L'effet bloquant du carbone sur la diffusion du bore est alors meilleur et le dopant est mieux contenu dans la base Si/SiGeC:B. Cette meilleure incorporation du carbone se reflète dans les résultats électriques. Le courant IB n'augmente pas aux fortes concentrations de carbone, ce qui signifie qu'il n'y a pas de centres recombinants dans la base. Le courant IC et la fréquence fT augmentent aussi, ce qui suggère que la largeur de la base neutre est plus fine et donc que la diffusion du bore est ralentie.<br />Nous avons également mis en évidence l'existence d'une corrélation entre le courant IB et l'intensité du signal de photoluminescence à température ambiante. En effet, considérant que leurs mécanismes de recombinaison sont similaires, nous avons noté que la hausse de IB correspond à la chute de la photoluminescence.
475

Complexes Excitoniques dans des Boîtes Quantiques Naturelles dans des Structures GaAs/AlAs de type II.

Pietka, Barbara 27 July 2007 (has links) (PDF)
Des boîtes quantiques à fort confinement tridimensionnel et de très basse densité (106cm-2) ont été démontrées dans des structures qui ont été originellement développées comme des double puits quantique de GaAs/AlAs avec des barrières de GaAlAs. Le fait que ces structures soient de type II permet de détecter les boîtes quantiques très facilement grâce à la très longue durée de vie des excitons indirects (de l'ordre de quelques millisecondes) et à leur capacité à diffuser efficacement (jusqu'à 100mm) dans les pièges zéro dimensionnels. Cet effet est généralement difficile à obtenir dans les structures directes. Les boîtes quantiques peuvent donc être facilement remplies par des excitons, provoquant la formation, non seulement d'excitons, mais aussi d'excitons chargés et de biexcitons, et également de molécules excitoniques plus complexes montrant un caractère zéro dimensionnel.<br />Ce travail est consacré à l'étude des complexes excitoniques fortement confinés, à leur nature et aux processus permettant leur formation.<br />Nous présentons des études spectroscopiques de l'émission d'une boîte quantique unique sous différentes conditions d'excitation et détectée de différentes manières.<br /> La possibilité de contrôler optiquement le nombre d'électrons et de trous qui occupent les niveaux discrets des boîtes quantiques nous a permis d'étudier la formation de complexes multi-excitoniques en fonction de la densités d'excitons. Les effets observés sont décrits par le modèle de la normalisation des bandes d'énergie comprenant les effets multi-corps, les interactions d'échange et les effets de corrélation.<br />L'influence d'un champ magnétique sur les complexes multi-excitoniques est d'abord discutée. De manière générale, il est montré comment l'application d'un champ magnétique modifie la structure énergétique des transitions observées. Des propriétés typiques de boîtes quantiques telles que l'effet Zeeman, décalage diamagnétique et l'énergie de liaison excitonique sont discutées. Ces études ont permis une analyse de la symétrie et de la taille du potentiel de confinement des boîtes.<br />Ensuite, les mécanismes de capture d'excitons dans les boîtes sont considérés. Le rôle important des processus de diffusion contribuant au temps de relaxation de l'émission des boîtes quantiques uniques est discuté sur la base d'expériences de spectroscopie résolue en temps.<br />Le rôle des processus radiatifs et non radiatifs dans l'émission de complexes multi-excitoniques est montré dans l'émission thermiquement activée de boîtes quantiques uniques.<br />Les mesures de corrélation de photon ont permis la classification des différentes lignes d'émission des complexes multi-excitoniques, d'étude du caractère de mécanisme de capture des porteurs photo-créés et la dynamique des fluctuations de charge caractéristiques d'une boîte quantique unique.<br />L'approche expérimentale à un problème de boîte quantique unique est largement discutée et des modèles théoriques sont appliqués pour décrire les effets observés.
476

Développement d'environnements automatisés pour des applications dans le domaine de l'optique

Paccou, Laurent Douay, Marc Hedoux, Alain Guinet, Yannick January 2007 (has links)
Reproduction de : Thèse de doctorat : Instrumentation et analyses avancées : Lille 1 : 2005. / N° d'ordre (Lille 1) : 3638. Titre provenant de la page de titre du document numérisé. Bibliogr. à la suite des chapitres. Liste des publications et communications.
477

Reactive replacement and addition of cations in bioclastic silica and calcite

Allan, Shawn Michael. January 2005 (has links)
Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2005. / Committee Chair: Kenneth Sandhage; Committee Members: Joe Cochran, Robert Snyder and Tom Sanders. Part of the SMARTech Electronic Thesis and Dissertation Collection.
478

Self-assembled quantum dots in advanced structures

Creasey, Megan Elizabeth 09 July 2013 (has links)
Advances in nanofabrication have bolstered the development of new optical devices with potential uses ranging from conventional optoelectronics, such as lasers and solar cells, to novel devices, like single photon or entangled photon sources. Quantum encryption of optical communications, in particular, requires devices that couple efficiently to an optical fiber and emit, on demand, indistinguishable photons. With these goals in mind, ultrafast spectroscopy is used to study the electron dynamics in epitaxially grown InAs/GaAs quantum dots (QDs). Quantifying the behavior of these systems is critical to the development of more efficient devices. Studies of two newly developed InGaAs QD structures, quantum dot clusters (QDCs) and QDs embedded in photonic wires, are presented herein. GaAs photonic wires with diameters in the range of 200 to 250 nm support only the fundamental HE11 guided mode. To fully quantify these new systems, the emission dynamics of QDs contained within wires in a large range of diameters are studied. Time correlated single photon counting measurements of the ground state exciton lifetimes are in very good agreement with predicted theoretical values for the spontaneous emission rates. For diameters smaller than 200 nm, QD emission into the HE11 mode is strongly inhibited and non-radiative processes dominate the decay rate. The best small diameter wires exhibit inhibition factors as high as 16, on par with the current state of the art for photonic crystals. The QDCs are the product of a hybrid growth technique that combines droplet heteroepitaxy with standard Stranski-Krastanov growth to create many different geometries of QDs. The work presented in this dissertation concentrates specifically on hexa-QDCs consisting of six InAs QDs around a GaAs nanomound. The first ever spectral and temporal properties of QDs within individual hexa-QDCs are presented. The QDs exhibit narrow exciton resonances with good temperature stability, indicating that excitons are well confined within individual QDs. A distinct biexponential decay is observed even at the single QD level. This behavior suggests that non-radiative decay mechanisms and exciton occupation of dark states play a significant role in the recombination dynamics in the QDCs. / text
479

Carrier Lifetime Relevant Deep Levels in SiC

Booker, Ian Don January 2015 (has links)
Silicon carbide (SiC) is currently under development for high power bipolar devices such as insulated gate bipolar transistors (IGBTs). A major issue for these devices is the charge carrier lifetime, which, in the absence of structural defects such as dislocations, is influenced by point defects and their associated deep levels. These defects provide energy levels within the bandgap and may act as either recombination or trapping centers, depending on whether they interact with both conduction and valence band or only one of the two bands. Of all deep levels know in 4H-SiC, the intrinsic carbon vacancy related Z1/2 is the most problematic since it is a very effective recombination center which is unavoidably formed during growth. Its concentration in the epilayer can be decreased for the production of high voltage devices by injecting interstitial carbon, for example by oxidation, which, however, results in the formation of other new deep levels. Apart from intrinsic crystal flaws, extrinsic defects such as transition metals may also produce deep levels within the bandgap, which in literature have so far only been shown to produce trapping effects. The focus of the thesis is the transient electrical and optical characterization of deep levels in SiC and their influence on the carrier lifetime. For this purpose, deep level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS) variations were used in combination with time-resolved photoluminescence (TRPL). Paper 1 deals with a lifetime limiting deep level related to Fe-incorporation in n-type 4H-SiC during growth and papers 2 and 3 focus on identifying the main intrinsic recombination center in p-type 4H-SiC. In paper 4, the details of the charge carrier capture behavior of the deeper donor levels of the carbon vacancy, EH6/7, are investigated. Paper 5 deals with trapping effects created by unwanted incorporation of high amounts of boron during growth of n-type 4H-SiC which hinders the measurement of the carrier lifetime by room temperature TRPL. Finally, paper 6 is concerned with the characterization of oxidation-induced deep levels created in n- and p-type 4H- and 6H-SiC as a side-product of lifetime improvement by oxidation. In paper 1, the appearance of a new recombination center in n-type 4H-SiC, the RB1 level is discussed and the material is analyzed using room temperature TRPL, DLTS and pnjunction DLTS. The level appears to originate from a reactor contamination with Fe, a transition metal that generally leads to the formation of several trapping centers in the bandgap. Here it is found that under specific circumstances beneficial to the growth of high-quality material with a low Z1/2 concentration, the Fe incorporation also creates an additional recombination center capable of limiting the carrier lifetime. In paper 2, all deep levels found in p-type 4H-SiC grown at Linköping University which are accessible by DLTS and MCTS are investigated with regard to their efficiency as recombination centers. We find that none of the detectable levels is able to reduce carrier lifetime in p-type significantly, which points to the lifetime killer being located in the top half of the bandgap and having a large hole to electron capture cross section ratio (such as Z1/2, which is found in n-type material), making it undetectable by DLTS and MCTS. Paper 3 compares carrier lifetimes measured by temperature-dependent TRPL measurements in n- and p-type 4H-SiC and it is shown that the lifetime development over a large temperature range (77 - 1000 K) is similar in both types. This is interpreted as a further indication that the carbon vacancy related Z1/2 level is the main lifetime killer in p-type. In paper 4, the hole and electron capture cross sections of the near midgap deep levels EH6/7 are characterized. Both levels are capable of rapid electron capture but have only small hole capture rates, making them insignificant as recombination centers, despite their advantageous position near midgap. Minority carrier trapping by boron, which is both a p-type dopant and an unavoidable contaminant in 4H-SiC grown by CVD, is investigated in paper 5. Since even the shallow boron acceptor levels are relatively deep in the bandgap, minority trap and-release effects are detectable in room-temperature TRPL measurements. In case a high density of boron exists in n-type 4H-SiC, for example leached out from damaged graphite reactor parts during growth, we demonstrate that these trapping effects may be misinterpreted in room temperature TRPL measurements as a long free carrier lifetime. Paper 6 uses MCTS, DLTS, and room temperature TRPL to characterize the oxidation induced deep levels ON1 and ON2 in n- and p-type 4H- and their counterparts OS1-OS3 in 6H-SiC. The levels are found to all be positive-U, coupled two-levels defects which trap electrons efficiently but exhibit very inefficient hole capture once the defect is fully occupied by electrons. It is shown that these levels are incapable of significantly influencing carrier lifetime in epilayers which underwent high temperature lifetime enhancement oxidations. Due to their high density after oxidation and their high thermal stability they may, however, act to compensate n-type doping in low-doped material.
480

Optische Eigenschaften von Versetzungen in Silizium

Allardt, Matthias 24 August 2015 (has links) (PDF)
Versetzungen sind linienhafte Störungen in Kristallen und beeinflussen die mechanischen, elektrischen und optischen Eigenschaften des Halbleitermaterials. In dieser Arbeit werden die optischen Eigenschaften von Versetzungen in Silizium anhand des Studiums ihrer charakteristischen Lumineszenz, der sogenannten D-Linien, untersucht. Dabei wurden die Versetzungen in einkristallinen Siliziumproben verschiedener Orientierung in einem einstufigen Prozess mittels plastischer Verformung bei hohen Temperaturen erzeugt und ggf. in einem zweiten Schritt durch Hochlastverformung bei tieferen Temperaturen modifiziert. Als Methoden zur Untersuchung der optischen Eigenschaften der Versetzungen werden Photolumineszenz (PL)- und Kathodolumineszenz (KL)-Spektroskopie verwendet. Gleitstufen an der Probenoberfläche werden mittels Rasterelektronenmikroskopie (REM), die Versetzungsanordnungen im Probenvolumen mittels Transmissionselektronenmikroskopie (TEM) abgebildet. Die Versetzungsstruktur der auf Einfachgleitung orientierten Proben ist durch relaxierte Versetzungen (einstufige Verformung) bzw. gerade Versetzungen (zweistufige Verformung) gekennzeichnet. In der auf Vielfachgleitung orientierten Probe werden mehrere Gleitsysteme gleichartig aktiviert. Es bildet sich ein Zellmuster aus, wobei das Innere der ca. 1 µm großen Zellen im Wesentlichen versetzungsfrei ist und die Zellwände eine hohe Versetzungsdichte aufweisen. Generell sind die mittleren Versetzungsdichten aller Proben hoch. Sie betragen zwischen 5 x 10^7 und 1 x 10^9 cm-2. Die Lumineszenz der einstufig verformten Proben ist durch das Auftreten von vier Linien (D1 bis D4) im Spektrum gekennzeichnet. In den zweistufig verformten Proben dominieren die Linien D5 und D6 die Lumineszenz. Die spektralen Positionen aller D-Linien entsprechen den aus der Literatur bekannten Daten. Die integrale Lumineszenzintensität im Bereich der D-Linien nimmt mit wachsender mittlerer Versetzungsdichte zu. Zusätzlich kann in den zweistufig verformten Proben eine bisher nicht identifizierte Lumineszenzlinie bei einer Energie von 1,090 eV festgestellt werden. Für diese Linie wird in dieser Arbeit die Bezeichnung P^2SD verwendet. In den KL-Abbildungen wird für alle D-Linien und die P^2SD-Linie im Wesentlichen eine örtlich homogene Lumineszenzverteilung festgestellt. Dies wird auf eine im Maßstab des KL-Wechselwirkungsvolumens homogene Versetzungsverteilung zurückgeführt. Die lokalen Schwankungen der KL um die mittlere Intensität betragen maximal 15 %. Diese Schwankungen äußern sich in hellen und dunklen Lumineszenzstreifen, deren Breite deutlich größer als der mittlere Versetzungsabstand ist. Aus dem Vergleich von KL-Bildern mit Rückstreuelektronenbildern der Oberflächengleitstufen ergeben sich folgende Aussagen: Die KL-Intensität der D3- und D4-Linie ist auf markanten Gleitbändern im Vergleich zur Umgebung verringert, wogegen die Intensität der Linien D1 und D2 auf markanten Gleitbändern erhöht ist. Für die D5-Bande, die D6-, und die P^2SD-Linie kann kein allgemeiner Zusammenhang zwischen der Lokalisierung der Lumineszenz und der Gleitaktivität festgestellt werden. Anhand der experimentellen Ergebnisse kann die D3-Linie als TO-Phononenreplik der D4-Linie identifiziert werden. Für die D4-Lumineszenz werden zwei Rekombinationsmodelle diskutiert. Zum einen kann sie durch die exzitonische Rekombination an eindimensionalen Energiebändern erklärt werden, die durch das Verzerrungsfeld der Versetzungen von den jeweiligen Volumenenergiewerten abgespalten sind. Zum anderen kann auch die Rekombination eines tief gebundenen Elektrons mit einem schwach gebundenen Loch für die D4-Lumineszenz verantwortlich sein. In jedem Fall ist das Auftreten der D4-Linie an die Existenz von relaxierten 60 °- und Schraubenversetzungen gebunden. Die D1-Linie wird als OGamma-Phononenreplik der D2-Linie vorgeschlagen. Die D2-Linie selbst kann als ein strahlender Übergang zwischen zwei gebundenen Zuständen eines zweidimensionalen Potentialtopfs endlicher Tiefe modelliert werden. Die Abmessungen dieses Potentialtopfs sind dabei durch die Ausdehnung von Kinken und Jogs auf der Versetzungslinie gegeben. Allerdings könnte auch ein interner Übergang zwischen den Niveaus eines tiefen Defekts innerhalb der Bandlücke als Erklärung herangezogen werden. Wegen der Zunahme der Lumineszenzintensiät der D2-Linie durch thermische Behandlungen sollten Kinken, Jogs, und Punktdefekte im Verzerrungsfeld der Versetzungen als Ursache der D2-Lumineszenz in Frage kommen. Auch die P^2SD-Linie kann mithilfe von zwei unterschiedlichen Rekombinationsmodellen erklärt werden (free-to-bound-Übergang oder exzitonische Rekombination an zweidimensionalen Energiebändern). Punktdefekte, die während des zweistufigen Verformungsprozesses entstehen, könnten die P^2SD -Linie hervorrufen.

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