The present work has been focused on the growth of Group III-nitride epitaxial layers and nanostructures on Si (111) substrates by plasma-assisted molecular beam epitaxy. Silicon is regarded as a promising substrate for III-nitrides, since it is available in large quantity, at low cost and compatible to microelectronics device processing. However, three-dimensional island growth is unavoidable for the direct growth of GaN on Si (111) because of the extreme lattice and thermal expansion coefficient mismatch. To overcome these difficulties, by introducing β-Si3N4 buffer layer, the yellow luminescence free GaN can be grow on Si (111) substrate. The overall research work carried out in the present study comprises of five main parts. In the first part, high quality, crack free and smooth surface of GaN and InN epilayers were grown on Si(111) substrate using the substrate nitridation process. Crystalline quality and surface roughness of the GaN and InN layers are extremely sensitive to nitridation conditions such as nitridation temperature and time. Raman and PL studies indicate that the GaN film obtained by the nitridation sequences has less tensile stress and optically good. The optical band gaps of InN are obtained between ~0.73 to 0.78 eV and the blueshift of absorption edge can be induced by background electron concentration. The higher electron concentration brings in the larger blueshift, due to a possible Burstein–Moss effect. InN epilayers were also grown on GaN/Si(111) substrate by varying the growth parameters such as indium flux, substrate temperature and RF power. In the second part, InGaN/Si, GaN/Si3N4/n-Si and InN/Si3N4/n-Si heterostructures were fabricated and temperature dependent electrical transport behaviors were studied. Current density-voltage plots (J-V-T) of InGaN/Si heterostructure revealed that the ideality factor and Schottky barrier height are temperature dependent and the incorrect values of the Richardson’s constant produced, suggests an inhomogeneous barrier at the heterostructure interface. The higher value of the ideality factor compared to the ideal value and its temperature dependence suggest that the current transport is primarily dominated by thermionic field emission rather than thermionic emission. The valence band offset of GaN/β-Si3N4/Si and InGaN/Si heterojunctions were determined by X-ray photoemission spectroscopy. InN QDs on Si(111) substrate by droplet epitaxy and S-K growth method were grown in the third part. Single-crystalline structure of InN QDs (droplet epitaxy) was verified by TEM and the chemical bonding configurations of InN QDs were examined by XPS. The interdigitated electrode pattern was created and (I-V) characteristics of InN QDs were studied in a metal–semiconductor–metal configuration in the temperature range of 80–300 K. The I-V characteristics of lateral grown InN QDs were explained by using the trap model. A systematic manipulation of the morphology, optical emission and structural properties of InN/Si (111) QDs (S-K method) is demonstrated by changing the growth kinetics parameters such as flux rate and growth time. The growth kinetics of the QDs has been studied through the scaling method and observed that the distribution of dot sizes, for samples grown under varying conditions, has followed the scaling function. In the fourth part, InN nanorods (NRs) were grown on Si(111) and current transport properties of NRs/Si heterojunctions were studied. The rapid rise and decay of infrared on/off characteristics of InN NRs/Si heterojunction indicate that the device is highly sensitive to the IR light. Self-aligned GaN nanodots were grown on semi-insulating Si(111) substrate. The interdigitated electrode pattern was created on nanodots using photolithography and dark as well as UV photocurrent were studied. Surface band gaps of InN QDs were estimated from scanning tunneling spectroscopy (STS) I-V curves in the last part. It is found that band gap is strongly dependent on the size of InN QDs. The observed size-dependent STS band gap energy blueshifts as the QD’s diameter or height was reduced.

In der Dissertation wurde die Möglichkeit des gemeinsamen Recycling von Bleiglas und LCD-Glas zur Gewinnung der Hauptmetalle Blei und Indium (sowie weiterer Begleitmetalle) und die Erzeugung einer wirtschaftlich verwertbaren Glasphase untersucht. Durch die Anpassung der Glaszusammensetzung über die Zugabe von Soda und Kalk, die Einstellung der Arbeitstemperatur und die Untersuchung der prozesstechnischen Erfordernisse, wie die Trennung von Schmelzvorgang und Reduktion, konnte gezeigt werden, dass Blei zu über 98% und Indium zu über 80% aus den Schrotten gewonnen werden kann. Die erzeugte Glasphase ist durch Verdünnung mit Quarz und Feineinstellung der Zusammensetzung direkt verwendbar. Durch die Reduktion des Glases und die Kreislaufführung von zugeführtem Natriumoxid konnte gezeigt werden, dass sogar höherwertige Gläser hergestellt werden können. Die durchgeführte Wirtschaftlichkeitsbetrachtung der beiden Verfahrensalternativen bestätigte den ökonomischen Vorteil der Kreislaufführung.

In der vorliegenden Arbeit werden verschiedene Aspekte des Einflusses von Lokalisation, Unordnung und Polarisationsfeldern auf Elektron-Loch Zustände in Quantengräben (QWs von engl. quantum wells) aus Halbleitern mit großer Bandlücke theoretisch untersucht. Unter Verwendung eines Schwerpunktseparationsansatzes wird das Verhalten von QW Exzitonen und Biexzitonen im Grenzfall schwacher Lokalisation beschrieben. Es zeigt sich, daß die Lokalisationsenergie des Biexzitons mehr als doppelt so groß ist wie die des Exzitons. Dies wird verursacht durch ein universelles Gesetz der Lokalisation in schwachen zwei-dimensionalen Potentialen, welches lediglich durch das "Potentialvolumen" und die Masse des lokalisierten Teilchens bestimmt wird. Ein einfaches Modell des QW Biexzitons wird entwickelt, dessen Ergebnisse gut mit jenen übereinstimmen, die man mit Hilfe eines aufwendigeren numerischen Modells erhält. Der Grenzfall starker Lokalisation von QW Exzitonen und höheren Exzitonenkomplexen wird mittels einer Dichtefunktionalrechnung untersucht. Es wird gezeigt, daß Zustände bis mindestens zum X4 in den nm-großen Potentialminima lokalisieren können, die durch Phasenseparation in (In,Ga)N/GaN QWs enstehen. Es wird das Übergangsspektrum des sukzessiven Zerfalls eines lokalisierten X4 berechnet. Auf Grundlage der selbstkonsistenten Lösung von Poisson- und Schrödinger-Gleichung wird der Einfluß des Probendesigns von (In,Ga)N/GaN QW-Strukturen auf den makroskopischen Verlauf des Polarisationsfeldes in Wachstumsrichtung und somit auf optische Übergangsenergie und Oszillatorstärke systematisch untersucht. Besondere Bedeutung kommt dabei der Abschirmung der Felder durch Raumladungszonen zu. Es wird gezeigt, daß die Position des QW bezüglich einer ausgedehnten Oberflächen-Verarmungszone - die in n-dotierten, Ga-polarisierten Proben auftritt - erheblichen Einfluß auf Übergangsenergie und Oszillatorstärke hat. Durch die räumliche Variation der Polarisationsfeldstärke in dieser Verarmungszone kann das optische Übergangsspektrum eines Mehrfach-QW Schultern oder mehrere Maxima aufweisen. Indium Oberflächen-Segregation ruft eine Blauverschiebung der Übergangsenergie hervor, die bis zu einem Drittel der vom Polarisationsfeld verursachten quantum confined Stark-Verschiebung kompensiert. Diese Blauverschiebung wird von einer Verringerung des Elektron-Loch Überlapps begleitet. Die Polarisationsfelder in (In,Ga)N/GaN Mehrfach-QWs verschmieren das stufenförmige Einteilchen-Absorptionsspektrum. Durch die Aufhebung der näherungsweisen Diagonalität von Inter-Subband Übergängen und durch die Miniband-Dispersion in höheren, gekoppelten Zuständen haben diese Felder, neben dem Beitrag von Potentialfluktuationen, einen entscheidenden Einfluß auf die Form des Absorptionsspektrums. Ein in der Literatur diskutierter Mechanismus, der allein durch Polarisationsfelder eine Verbreiterung optischer Spektren hervorruft, kann nicht bestätigt werden. Unter Annahme einer unkorrelierten Zusammensetzung von (In,Ga)N und einer lateral korrelierten Grenzflächenrauhigkeit von einer Monolage in jeder Grenzfläche zeigt die spektrale Breite des Exzitonen-Schwerpunktpotentials eine Verschmälerung mit zunehmendem Feld. Diese wird verursacht durch das Eindringen der Teilchen in die binären Barrieren und durch ein vergrößertes Exzitonenvolumen. Im Fall einer langreichweitigen Grenzfächenrauhigkeit findet man eine Aufspaltung des Spektrums in einzelne Linien. / In this thesis, various aspects of the influence of localization, disorder, and polarization fields on electron-hole states in wide-gap semiconductor quantum wells (QWs) are investigated theoretically. A theoretical treatment of quantum well exciton and biexciton states in the limit of weak localization is presented, using a center-of-mass separation ansatz. It shows that the localization energy of the biexciton is more than twice as large as that of the exciton due to the universal behaviour of localization in weak two-dimensional potentials which is ruled only by the potential "volume" and the mass of the localized particle. A useful simple model of the QW biexciton wavefunction is developed which provides good agreement with the results obtained with an extensive numerical solution. The limit of strong localization of QW excitons and higher exciton complexes is investigated with a density functional calculation. It is demonstrated that states at least up to X4 may localize in nm-scale potential boxes caused by indium phase separation in (In,Ga)N/GaN QWs. The transition spectrum of the successive recombination of a localized X4 is calculated. A systematic investigation of the influence of the sample design of (In,Ga)N/GaN QW structures on optical transition energy and oscillator strength reveals the importance of space charge layers with regard to screening of polarization fields along the QW-axis. Based on a self-consistent solution of the Schrödinger-Poisson equations, the overall situation of the macroscopic spontaneous and piezoelectric polarization fields is discussed in dependence on various substantial sample parameters. It is found that the position of a QW in the sample with respect to an extended surface depletion layer - which is shown to exist in n-type Ga-face grown material - severely affects transition energy and electron-hole overlap. Due to the spatial variation of the field strength in this surface depletion layer, the optical transition spectrum of a Ga-face grown multiple-QW can display shoulders or even a multiple-peak structure. Indium surface segregation results in a blueshift of the transition energy compensating up to one third of the quantum confined Stark shift produced by the polarization field. This blueshift is accompanied by a decrease of the electron-hole overlap. Polarization fields in (In,Ga)N/GaN multiple-QWs result in a smoothing of the step-like single-particle absorption spectrum. Apart from the contribution of compositional fluctuations, the fields have significant influence on the shape of the spectrum via the abrogation of the nearly diagonality of inter-subband transitions and via the mini-band dispersion of higher coupled states in case of a periodic structure. A line broadening-mechanism due to polarization fields in (In,Ga)N/GaN QWs, as sometimes discussed in literature, could not be confirmed. Assuming uncorrelated (In,Ga)N alloy and in-plane-correlated interface roughness of one monolayer in each interface, the calculation of the spectral width of the QW exciton center-of-mass potential yields a narrowing with increasing average field. This is a result of the penetration of the carriers into the barriers and of an increasing exciton volume. In case of a long-range interface roughness, a splitting of the spectrum into individual lines can be predicted.

This research was designed to fabricate and characterize novel polyhedral phase segregated microstructures of polystyrene (PS)-matrix composites filled with multi-walled carbon nanotubes (MWNT) and indium tin oxide (ITO) nanopowders. PS-composites were compression molded with MWNT and ITO separately first. The resulting composites were conducting, and remained optically transparent. Mixtures of MWNT and ITO were then used to form mixed ITO/MWNT PS-composites in order to optimize their transparency and conductivity. This was achieved by fabricating composites with varying concentrations of fillers. Impedance spectroscopy was used to characterize the electrical properties of the PS-composites. Optical properties were characterized by measuring the transmission of light through the PS-composite in the visible light spectrum using a spectrophotometer. The electrical properties and microstructural attributes of the fillers used were also characterized. The main objective of the project was to understand the relationships between the structural, electrical, and optical properties of the PS-composites. The resistivity of PS-composites filled with MWNT ranged from 105 to 1013 Ω cm for samples with 0.007 to 0.9 vol% MWNT. The resistivity of PS-composites filled with ITO ranged from 107 to 1013 Ω cm for PS-composites with 0.034 to 0.86 vol% ITO. PS/ITO composites had a percolation threshold of 0.15, 0.25, or 0.3 phr ITO, depending on the type of ITO used in the composite. The percolation threshold of PS/MWNT composites was found to be 0.01 phr MWNT. Mixed ITO/MWNT PS-composites were already percolated, the concentrations investigated in xv ii this study were already above the percolation threshold of these composites. A time dependence on impedance was found for PS-composites filled with MWNT. As time increases there is a decrease in impedance, and in some cases also a dependence on voltage. All PS-composites showed a dependence on the microstructure of the PS matrix and the filler material. The resistivity and percolation threshold were lower for PS/MWNT composites than PS/ITO composites due to the difference in filler size and aspect ratio, since MWNT have a smaller size. The orientation of PS grains with respect to neighboring grains was found to affect the resistivity of PS/MWNT. PS/MWNT composites with preferentially oriented PS grains were found to have a lower resistivity. Mixed ITO/MWNT PS-composites with the right filler concentrations were able to maintain transmission while decreasing resistivity. The fracture surface of fractured PS-composites prepared in this work indicated that there was bonding between adjacent PS-grains. From this work, it can be concluded that large grain hybrid ITO/MWNT PS-composites provide insight into the effect of combining nanometer sized filler materials together in a polymer matrix on the resultant structural, electrical, and optical properties of the composite. In the future, it is recommended that this study be used to aid research in flexible transparent conducting electrodes using a polymer matrix and hybrid/mixed nanometer sized conducting fillers.

Dans le cadre d' une recherche sur les détecteurs de neutrinos solaires de basse énergie, une étude cristallochimique et optique sur des oxydes et fluorures d'indium a été effectuée. Les cristaux des phases étudiées ont été préparés par des méthodes appropriées telles que la méthode du flux, la méthode de transport en phase gazeuse et la méthode de Bridgman. Les études structurales et de la luminescence ont été réalisées sur les poudres ou/et sur les monocristaux. Des propriétés luminescentes ont été mises en évidence pour plusieurs oxydes d'indium. Elles ont été attribuées a des transitions ayant un caractère de transfert de charge entre l' indium et l' oxygène dans le cas de In2TiO5, In2Si2O7 et In2Ge2O7, entre le tungstene et l'oxygène dans celui de In6WO12. Les durées de vie des états excites sont de l'ordre quelques microsecondes a très basse température. La luminescence de Ce3+ au sein de différents réseaux-hôtes, borate d'indium et de scandium, fluoroindates de type elpasolite A2A'InF6 (A=Rb, K A=K, Na) a été caractérisée. Une hypothèse basée sur le couple oxydo-réducteur In(III)-Ce(III) a été proposée pour expliquer l'extinction progressive de la luminescence bleu-vert du Ce(III) au site de l' In(III) dans les fluorures sous l' effet d' une irradiation dans les bandes 4f->5d avec apparition simultanée d'une émission rouge, phenomène optiquement et thermiquement réversible. La structure inedite du fluoroindate de lithium, LiInF4, a été resolue.

Includes vita. / Title from PDF of title page. / Document formatted into pages; contains 204 pages. / Thesis (Ph.D.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: The goal of this research project was to contribute to the understanding of CuGaSe2/CdS photovoltaic devices, and to improve the performance of these devices. The initial part of the research dealt with the optimization of a Sequential Deposition process for CuIn(Ga)Se2 absorber formation. As an extension of this, a recipe (Type I Process) for CuGaSe2 absorber layer fabrication was developed, and the deposition parameters were optimized. Electrical characterization of the thin films and completed devices was carried out using techniques such as Two-Probe and Three-Probe Current-Voltage, Capacitance-Frequency, Capacitance-Voltage, and Spectral Response measurements. Structural/chemical characterization was done using XRD and EDS analysis. Current densities of up to 15.2 mA/cm2, and Fill Factors of up to 58% were obtained using the Type I CuGaSe2 Process. VOC's, however, were limited to less than 700 mV. / ABSTRACT: Several process variations, such as changes in the rate/order/temperature of depositions and changes in the thickness of layers, resulted in little improvement. With the aim of breaking through this VOC performance ceiling, a new absorber recipe (Type II Process) was developed. VOC's of up to 735 mV without annealing, and those of up to 775 mV after annealing, were observed. Fill Factors were comparable to those obtained with Type I Process, whereas the Current Densities were found to be reduced (typically, 10-12 mA/cm2, with the best value of 12.6 mA/cm2). This performance of Type II devices was correlated to a better intermixing of the elements during the absorber formation. To gain an understanding of the performance limitations, two simulation techniques, viz. SCAPS and AMPS, were used to model our devices. / ABSTRACT: Several processing experiments and SCAPS modeling indicate that a defective interface between CuGaSe2 and CdS, and perhaps a defective absorber layer, are the cause of the VOC limitation. AMPS simulation studies, on the other hand, suggest that the back contact is limiting the performance. Attempts to change the physical back contact, by changes in the absorber processing, were unsuccessful. Processing experiments and simulations also suggest that the CuGaSe2/CdS solar cell involves a true heterojunction between these two layers. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

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The physical and chemical properties of In- and Au- interfaces with In[0.53]Ga[0.47]As/InP(100) and In[0.52]Al[0.48]As(100) formed at room and low temperatures have been studied. Current-voltage measurements have indicated that In contacts to Ino[0.53]Ga[0.47]As(100) formed at 80K exhibit significantly higher Schottky barriers (&phis;b=0.45 eV) than In diodes formed at 294K (&phis;b=0.30 eV), whereas Au diodes formed on In[0.53]Ga[0.47]As(100) at either low temperature or room temperature exhibit Ohmic behaviour. The reactions occurring during interface formation at room and low temperatures have been investigated using soft X-ray photoemission spectroscopy (SXPS) and Transmission Electron Microscopy (TEM).The results presented show that In metallisation of In[0.53]Ga[0.47]As(100) at room temperature results in a predominantly three dimensional mode of growth, accompanied by the out-diffusion of As. Low temperature (125K) metallisation appears to reduce clustering and inhibit As out-diffusion. Examination of the resulting interfaces by TEM confirm the more uniform nature of the metal layers formed at low temperature. Metallisation temperature seems to have little effect on the formation of Au-In[0.53]Ga[0.47]As(100) interfaces, other than to reduce the extent of overlayer clustering, with As out-diffusion apparent for both low and room temperature Au deposition. Interfaces formed between In and In[0.52]Al[0.48]As(100) at both low and room temperature were relatively abrupt with no out-diffusion of substrate species into the metal overlayer. Low temperature metallisation again appeared to reduce overlayer clustering, with TEM studies showing a smaller grain size at low temperature. Au deposition onto In[0.52]Al[0.48]As(100) produced similar interfaces formed at room and low temperature. As diffuses into the Au overlayer to form an Au/As compound at both temperatures, resulting in an interface that is complex and reacted. The degree of overlayer clustering is also thought to be much less pronounced for Au deposition compared to In deposition. Barrier heights measured by SXPS during the study, show good agreement with reported current-voltage measurements for Au and In diodes formed on both In[0.53]Ga[0.47]As/InP(100) and In[0.52]Al[0.48]As(100). Possible mechanisms for the observed adaptation of the pinning position are discussed in the context of current models of Schottky barrier formation.

Ce travail de thèse a pour sujet l'étude de transistors en couches minces (TFTs) à base d'Indium Gallium Zinc Oxide (IGZO). Nous nous sommes intéressés au procédé de réalisation des TFTs, et à la caractérisation des couches d'IGZO afin d'obtenir les caractéristiques au plus près de l'état de l'art. Nous avons également étudié le processus de passivation, paramètre identifié comme critique pour stabiliser les TFT et atteindre de bonnes performances.Dans un premier temps, nous avons mis au point les conditions du dépôt de la couche active, et de la réalisation des TFTs. Les analyses morphologiques et structurales ont montré l'absence de cristallites de couche, ainsi qu'une surface peu rugueuse. La densité des porteurs de charge de la couche IGZO diminue lorsque le débit d'oxygène, variable durant son dépôt, augmente. La couche active déposée à 200°C et à 4 sccm d'oxygène présente une densité de porteurs de charge de l'ordre de 1E17 cm-3, valeur adaptée au fonctionnement des TFTs.Dans un second temps, nous avons évalué l'influence d'un recuit sur les caractéristiques des TFTs. Nous avons mis en évidence que le recuit sous oxygène conduit à des TFTs opérationnels, tandis que celui sous azote ou en absence de recuit induisent une suppression de l'effet de champ. Nos études ont également montré qu'une température de recuit de 300°C est favorable aux performances des transistors. Les premiers TFTs présentent des mobilités entre 5 et 15 cm2/Vs, des rapports ION/IOFF de l'ordre de 1E7, et des pentes sous le seuil d'environ 0.3 V/décade. Les tensions de seuil (VT), quant à elles, demeurent faibles donc restent à améliorer.Pour finir, nous avons étudié l'impact d'une couche de passivation sur les TFTs, en raison de la dégradation des caractéristiques de ces derniers dans l'atmosphère ambiante. Les couches de SiO2 (déposée par PECVD) et d'Al2O3 (déposée par ALD) ont été étudiées. Nous avons mis en évidence que ces passivations peuvent dégrader les TFTs au lieu de les protéger. VT tend à se décaler dans le sens négatif lorsque l'on augmente l'épaisseur de la couche d'Al2O3 ou le débit de Silane durant le dépôt du SiO2. Une des raisons principales de ce phénomène est la présence de l'hydrogène généré lors de la passivation. Nous avons évalué les solutions pour éviter la dégradation lors du dépôt et assurer une bonne protection du TFT. / This thesis aims to study thin-film transistors (TFTs) based on Indium Gallium Zinc Oxide (IGZO) in the framework of applications in active matrix flat panel LCD and OLED display. The TFT fabrication process and the characterization of IGZO deposited film are two key studies in this thesis in order to obtain TFT electrical characteristics close to the state-of-the-art. We have also studied the passivation which is identified as crucial for stabilizing the TFT and achieving good performance.The deposition of the active layer and the fabrication process of TFT are firstly studied. Smooth surface of deposited films is demonstrated by AFM and the absence of the crystalline peak of the material is shown by X-ray diffraction. The density of charge carriers decreases with the increase of oxygen flow rate. The active layer deposited at 200°C and at 4 sccm of oxygen flow has a carrier density in the order of 1E17 cm-3 which is suitable for TFT operation. This condition is chosen to fabricate IGZO-based TFT in this thesis.In a second step, we have evaluated the influence of annealing condition on TFTs' electrical characteristics. Annealing in oxygen leads to operational TFTs while doing the same under nitrogen or the absence of annealing suppresses field-effect behavior. Our studies have also shown that annealing temperature of 300°C is suitable to obtain good performance of the transistors. From this study, we have obtained TFTs with high mobility (between 5 and 15 cm2/Vs), high ION/IOFF ratios (about 1E7), and reasonable sub threshold slope (about 0.3 V/decade). The threshold voltage (VT) however remains low (between -4 and -2 V) and needs to be improved.Finally, we have investigated the impact of a passivation layer on the performance of IGZO TFTs. SiO2 film (deposited by PECVD) and Al2O3 film (formed by ALD) were studied. We have observed that such passivation can degrade the TFTs rather than protecting them. Concretely, VT shifts in negative direction when increasing the Al2O3 layer thickness or the silane flow during SiO2 deposition. Principal reason for this shift is the presence of hydrogen which is generated during passivation. We have evaluated some solutions to reduce the degradation during deposition and ensure a good protection of the TFTs.