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We have used deep level transient spectroscopy (DLTS) to characterise four defects with shallow levels in ZnO grown by pulsed laser deposition (PLD). These defects all have DLTS peaks below 100 K. From DLTS measurements and Arrhenius plots we have calculated the energy levels of these defects as 31 meV, 64 meV, 100 meV and 140 meV, respectively, below the conduction band. The 100 meV defect displayed metastable behaviour: Annealing under reverse bias at temperatures of above 130 K introduced it while annealing under zero bias above 110 K removed it. The 64 meV and 140 meV defects exhibited a strong electric field assisted emission, indicating that they may be donors.

We have used deep level transient spectroscopy (DLTS) to characterise four defects with shallow levels in ZnO grown by pulsed laser deposition (PLD). These defects all have DLTS peaks below 100 K. From DLTS measurements and Arrhenius plots we have calculated the energy levels of these defects as 31 meV, 64 meV, 100 meV and 140 meV, respectively, below the conduction band. The 100 meV defect displayed metastable behaviour: Annealing under reverse bias at temperatures of above 130 K introduced it while annealing under zero bias above 110 K removed it. The 64 meV and 140 meV defects exhibited a strong electric field assisted emission, indicating that they may be donors.

In der vorliegenden kumulativen Arbeit werden Untersuchungen am transparenten p-Typ Halbleiter Kupferiodid (CuI) beschrieben. Die Dünnschichtherstellung erfolgte mittels gepulster Laserabscheidung (PLD). Der Einfluss der Wachstumsbedingungen auf die strukturellen, morphologischen und elektrischen Eigenschaften wird dargelegt hinsichtlich des Ziels der Fabrikation funktioneller Schichten auf Basis von CuI. Dazu wird im ersten Teil der Arbeit der generelle Einfluss der PLD-Parameter auf das Schichtwachstum beschrieben. Ein dominierender Einfluss der Wachstumstemperatur auf die kristalline Qualität, Oberflächenrauhigkeit sowie Ladungsträgerdichte und Mobilität wurde beobachtet. Die 250nm dicken Dünnschichten zeigen im sichtbaren Bereich eine Transmittanz von bis zu 90%. Exzitonische Absorptions- und Lumineszenzcharakteristika konnten an solchen Schichten nachgewiesen werden. Eine schützende Deckschicht aus Al2O3 erwies sich als elementar zur Stabilisierung der elektrischen Eigenschaften und erlaubte die Fabrikation nicht-degenerierten Kupferiodids. Im zweiten Teil werden detail- lierte Untersuchungen des elektrischen Langzeitverhaltens von CuI in Abhängigkeit des Wachstums der Al2O3 Deckschichten diskutiert. Für Sauerstoff-defizientes Al2O3 zeigte das CuI komplexe elektrische Degradationsmechanismen, welche auf die Diffusion von Sauerstoff innerhalb der Heterostruktur zurückgeführt wurden. Die Ergebnisse beweisen einen dominierenden Einfluss extrinsischer Akzeptoren auf die elektrischen Eigenschaften von PLD gewachsenem CuI. Im Kontrast zum bisherigen Stand der Literatur spielen intrinsische Defekte für die Erklärung eine untergeordnete Rolle. Um eine Stabilisierung der Ladungsträgerdichten im Zusammenspiel mit Sauerstoff-defizientem Al2O3 zu er- reichen, wurden die CuI Dünnfilme mit Selen dotiert. Die Grenze zwischen Dotierung und Legierung, welche sich durch reduzierte Bandkantenenergien und eine einsetzende Phasenseparation definiert, wurde bestimmt. Weiterhin konnte die Bindungsenergie des Selen-Akzeptors in CuI bestimmt werden. Der finale Teil der Arbeit fokussierte sich auf die Unterdrückung der Bildung von Rotationsdomänen als dominierende Defekte von PLD gewachsenem CuI. Dieses Ziel wurde mittels PLD gewachsenen Natriumbromid (NaBr) Zwischenschichten auf kommerziellen Strontiumfluorid Substraten erreicht. Die Oberflächenrauigkeit von entsprechenden Dünnschichten ist deutlich reduziert. Unter Ausnutzung der hohen Wasserlöslichkeit von NaBr wurde ein epitaktischer Ablöseprozess entwickelt, der zur Herstellung frei stehender CuI Schichten geeignet ist. Das Wachstum von einkristallinen Volumenkristallen ist jedoch beschränkt, da bei Schichtdicken > 2 μm Defekthäufungen beobachtet werden und Rotationsdomänen auftreten.:1 Introduction 2 Theoretical Descriptions 2.1 Copper Iodide 2.1.1 Conductivity and Defect Chemistry 2.2 Epitaxy of Crystalline Thin Films 2.2.1 Stress and Strain 2.2.2 Heteroepitaxy of Copper Iodide 2.3 Electronic Defect States in Semiconductors 3 Experimental Methods 3.1 Sample Preparation by Pulsed Laser Deposition-PLD 3.1.1 Combinatorial and Eclipse PLD 3.2 Characterization Techniques 3.2.1 X-ray Diffraction-XRD 3.2.2 Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectrometry(EDX) 3.2.3 Atomic Force Microscopy-AFM 3.2.4 Laser Scanning Microscopy-LSM 3.2.5 Time-of-Flight Secondary Ion Mass Spectrometry - ToF-SIMS 3.2.6 Rutherford Backscattering-RBS 3.2.7 Hall-Effect 3.2.8 Spectroscopic Ellipsometry 3.2.9 Photoluminsescence Spectroscopy-PL 3.2.10 Transmission Spectroscopy 4 Cumulative Part 4.1 Optimization of Copper Iodide Thin Film Growth by Pulsed Laser Deposition 4.2 Origin of Free Charge Carriers and p-Doping of PLD Copper Iodide 4.3 Suppression of Rotational Domains, Volume Crystals and Epitaxial Lift-Off 5 Summary and Outlook Bibliography List of Abbreviations List of Publications Author Contributions Zusammenfassung nach Promotionsordnung §11(4) Selbstständigkeitserklärung

<p>The growth of CdTe thin films on Al₂O₃(0001) substrates by pulsed laser deposition from undoped pressed powder targets was studied. Thin film crystal structure was investigated by x-ray texture analysis as a function of plume flux, growth temperature and film thickness. Crystal texture increased for a decrease in plume flux. Single crystal CdTe (111) films were obtained by optimizing the plume flux. Increasing the growth temperature demonstrated a reduction in twin density. An optimum temperature of 300°C minimized the twin density without adverse desorption effects. The twin density decreased as an inverse squared function of film thickness. Single crystal CdTe films with comparable structural quality to Bridgeman single crystal wafers were grown under optimal conditions.</p> <p>The optoelectronic properties of CdTe films were investigated by photoluminescence and photoreflectance spectroscopy. The room temperature bandgap energy of 1.51 eV was consistent between spectroscopic measurements. Broadening parameters for spectra were consistent with reference high quality material. Low temperature photoluminescence spectra had a dominant emission consistent with bound excitons found in bulk CdTe. Emissions consistent with self-compensation or doping were not found. Hall effect and conductivity measurements at 300 K demonstrated high resistivity for undoped material and electron mobilities comparable to bulk CdTe for lightly doped films. Spectroscopic and electrical measurements of high structural quality CdTe films were consistent with high optoelectronic quality.</p> <p>An as-grown ability of the films to detach from their substrate was discovered. X-ray texture analysis and photoluminescence spectroscopy of films released onto rigid secondary carriers demonstrated that they maintained their structural and optoelectronic quality proceeding lift-off. Substrates having films released from them were found to be suitable for repeated growth. The technological relevance of this discovery is likely to drive further study into the lift-off phenomena and controlled doping of CdTe thin films.</p> / Master of Applied Science (MASc)

Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial materials. Reactive molecular-beam epitaxy (MBE) and pulsed-laser deposition (PLD) are the two most successful growth techniques for epitaxial heterostructures of complex oxides. PLD possesses experimental simplicity, low cost, and versatility in the materials to be deposited. Reactive MBE employing alternately-shuttered elemental sources (atomic layer-by-layer MBE, or ALL-MBE) can control the cation stoichiometry precisely, thus producing oxide thin films of exceptional quality. There are, however, major drawbacks to the two techniques. Reactive MBE is limited to source elements whose vapor pressure is sufficiently high; this eliminates a large fraction of 4- and 5-d metals. In addition, the need for ozone to maintain low-pressure MBE conditions increases system complexity in comparison to conventional PLD. On the other hand, conventional PLD using a compound target often results in cation off-stoichiometry in the films. This thesis presents an approach that combines the strengths of reactive MBE and PLD: atomic layer-by-layer laser MBE (ALL-Laser MBE) using separate oxide targets. Ablating alternately the targets of constituent oxides, for example SrO and TiO2, a SrTiO3 film can be grown one atomic layer at a time. Stoichiometry for both the cations and oxygen in the oxide films can be controlled. Using Sr1+xTi1-xO3, CaMnO3, BaTiO3 and Ruddlesden–Popper phase Lan+1NinO3n+1 (n = 4) as examples, the technique is demonstrated to be effective in producing oxide films with stoichiometric and crystalline perfection. By growing LaAl1+yO3 films of different stoichiometry on TiO2-terminated SrTiO3 substrate at high oxygen pressure, it is shown that the behavior of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface can be quantitatively explained by the polar catastrophe mechanism. / Physics

Multiferroics have attracted lots of research interest due to their potential in numerous multifunctional applications. The multiferroic materials could simultaneously exhibit two or more ferroic order parameters, and the coupling effects between ferroelectricity and ferromagnetism are named as magnetoelectric (ME) effect. Recently, with the development of thin film growth techniques, the multiferroics magnetoelectric composite heterostructures exhibit a very promising future prospects. This dissertation focused on the design, fabrication and characterization of new multiferroics magnetoelectric composite heterostructures. First, based on the specific phase architectures in BFO-CFO self-assembled thin films grown on variously oriented STO substrates and the epitaxial film growth knowledge, I designed two kinds of new film heterostructures: (i) I utilized self-assembled BFO nanopillars in a BFO-CFO two phase layer on (111) STO as a seed layer on which to deposit a secondary top BiFeO3 layer. The growth mechanism and multiferroic properties of these new heterostructures were investigated. (ii) I demonstrated the formation of a new quasi-(0-3) heterostructure by alternately growing (2-2) and (1-3) layers within the film. I proposed a new concept to overcome limitations of both the (2-2) and (1-3) phase connectivities and identified an indirect ME effect by the switching the characteristics of the piezoresponse for the new heterostructure. Second, for the option for candidates thin film materials with a high piezoelectric coefficient, which is a critical factor for ME composite films, I utilized the simple compositional BaSn0.11Ti0.89O3 bulk ceramic material as a target to grow films with the large piezoelectric properties. The grown high qualify lead-free epitaxial thin films had a chemical constituent similar to the reported giant piezoelectric ceramics near the MPB and with the QP. Both coherent and incoherent regions were observed in the interface and a larger piezoelectric coefficient d33 was achieved in this film. Finally, with respect to their characteristics and potential, I redirected from two-dimensional thin film materials to one-dimensional nanowire materials. By utilizing vertically aligned templates, I fabricated a new type of coaxial two-phase composite nanowires. Multiferroic properties of these new one-dimensional materials have been investigated. All these multiferroics magnetoelectric composite herterostructures would provide lots of potential in applications. / PHD

Les applications présentées dans cette thèse valorisent de diverses manières le principe d'ablation laser, c'est à dire l'arrachement de la matière d'une surface solide suite à l'irradiation avec un faisceau laser. Le plasma généré par irradiation laser impulsionnel a été utilisé pour le dépôt de couches minces ou de nanoparticules et pour l'analyse compositionnelle des couches d'épaisseur nanométrique. Nous avons synthétisé par dépôt laser combinatoire des librairies compositionnelles d'un oxyde mixte transparent d'In et Zn. En utilisant le plasma d'ablation pour le diagnostic compositionnel, nous avons déterminé les concentrations d'indium et de zinc dans les couches minces par spectroscopie laser. Des couches minces de bioverre ont été synthétisées par dépôt laser impulsionnel sur des substrats de titane. En contact avec des cellules ostéoblastes, les bioverres ont stimulé la prolifération et ont augmenté la viabilité. La prolifération des ostéoblastes cultivés sur les couches de bioverre a été 30% supérieure a l'échantillon de contrôle. On a déposé par PLD des couches minces ou nanoparticules adhérentes de ZnO sur des substrats textiles hydrophiles dans un flux d'oxygène ou sous vide pour obtenir des structures avec différentes mouillabilités. En augmentant le nombre d'impulsions laser de 10 à 100 nous avons observé la transition du recouvrement par des nanoparticules isolées vers des couches minces. En fonction de l'atmosphère environnant lors du dépôt, les couches minces et les nanoparticules ont changé leur mouillabilité, passant d'hydrophile en flux d'oxygène à un comportement superhydrophobe (angle de contact de 157°) en cas de dépôt sous vide. / The applications presented in this thesis exploit in different modes the principle of laser ablation, i.e. the material removal from a solid surface following irradiation with a pulsed laser beam. The plasma generated by laser ablation was used for thin films or nanoparticles deposition and for the compositional analysis of nanometric thin films. We synthesized by combinatorial pulsed laser deposition, thin film libraries of a complex oxide of In and Zn. Using the ablation plasma for compositional diagnostic, we determined the In and Zn concentrations in films by Laser Induced Breakdown Spectroscopy using a procedure based on the spectral luminance calculation of a plasma in local thermodynamic equilibrium. Thin films of bioactive glass were synthesized by pulsed laser deposition, magnetron sputtering and MAPLE on Ti substrates and tested the transfer accuracy by physico-chemical tests and their functionality in vitro. In contact with human osteoblast cells, the bioactive glasses stimulated their proliferation and enhanced their viability. The proliferation of osteoblasts cultivated on bioactive films was 30% superior to the control sample. ZnO thin films or nanoparticles were deposited on hydrophilic textile substrates in oxygen flux or in vacuum in order to obtain structures with different wetting behavior. Increasing the number of laser pulses from 10 to 100, we observed a coating transition from isolated nanoparticles to thin films fully coating the textile fibers. Function of the ambient atmosphere during experiments, the structures changed their wetting behavior, passing from hydrophilic in oxygen flux to superhydrophobic (157°) in case of deposition in vacuum.