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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

In this thesis, the structural, optical, and electrical properties of wurtzite MgxZn1-xO:Al and MgxZn1-xO:Ga thin films have been investigated in dependence on Mg and dopant concentration. Among the transparent conductive oxides (TCOs), ZnO based compounds have gained renewed interest as a transparent electrode for large scale applications such as defroster windows, at panel displays, touch screens, and thin film solar cells due to low material and processing cost, non-toxicity, and suitable physical properties. In general, these applications require transparent electrodes with lowest possible resistivity of rho < 10^-3 Ohmcm and lower [1]. Recently, it has been reported that Ga and Al doped ZnO thin films can be deposited with respective resistivity of 5x10^-5 Ohmcm [2] and 3 x10^-5 Ohmcm [3] which are similar to the data obtained for other practical TCOs, i.e. the resistivity of about 4x 10^-5 Ohmcm for Sn doped In2O3 (ITO) thin films [4]. Moreover, the bandgap of ZnO can be increased by alloying with Mg offering band alignment between transparent electrode and active (or buffer) layer of the device, e.g. Cu(In,Ga)Se2 solar cells [5]. The tunable bandgap of these transparent electrodes can further increase the efficiency of the devices by avoiding energy losses in the interface region of the layers. From this point of view, this work has been aimed to investigate the doping efficiency and limits in transparent conductive (Mg,Zn)O alloys. For this purpose, the samples investigated in this work have been grown by pulsed-laser deposition (PLD) using a novel, continuous composition spread method (CCS). In general, this method allows to grow thin films with lateral composition gradient(s) [6, 7]. All MgxZn1-xO:Al and MgxZn1-xO:Ga thin films have been deposited on 2-inch in diameter glass, c- or r-plane sapphire substrates using threefold segmented PLD targets in order to grow thin films with two perpendicular, lateral composition gradients, i.e. the Mg composition is varied in one direction whereas the Al/Ga concentration is varied in a perpendicular direction [7, 8]. In order to investigate the influence of the temperature, samples grown at different substrate temperatures in the range of 25 to 600 C were investigated. The optical and electrical measurements have been carried out on (5x 5)mm^2 samples that were cut from the CCS wafers along the respective composition gradients, i.e. Mg and Al/Ga contents. Subsequently, physical properties of thin films have been analyzed for a large range of Al/Ga content between 0.5 and 7 at.%, which corresponds to doping concentrations between 2x 10^20 and 3x 10^21 cm^-3, for different Mg contents x(Mg) ranging from 0.01 to 0.1. It has been found that practically the limiting the dopant concentrations is about 2 x10^21 cm^-3. Further, the electrical data suggests, that the compensating intrinsic defect is doubly chargeable hinting to the zinc vacancy (V_Zn) as microscopic origin. Increasing the dopant concentration above 2 x10^21 cm^-3 leads to a degradation of electrical and structural properties [8]. Further, the influence of growth and annealing temperatures on structural, electrical and optical properties of the films has been studied. For that purpose, Al and Ga doped (2.5 at.% = 1x10^21 cm^-3) Mg0.05Zn0.95O thin films have been chosen from CCS samples grown at T_g = (25 - 600) C . For both doping series, the samples grown at higher temperatures exhibit better crystalline quality compared to the samples grown at lower growth temperatures. As a result, samples grown at higher temperatures reveal higher Hall mobility. For the Al-doping series, the highest free charge carrier density of n = 8.2x 10^20 cm^-3 was obtained for an Mg0.05Zn0.95O:Al thin film grown at 200 C, with corresponding Hall mobility of mu = 13.3 cm^2/Vs, a resistivity of rho = 5.7x10^-4 Ohmcm, and optical bandgap of E_g = 3.8 eV. Interestingly, the free charge carrier density of n = (5 - 8) x 10^20 cm^-3 for samples grown with T_g > 300 C is clearly higher than the value of n = 1.25 x 10^20 cm^-3 that was obtained for the high temperature grown sample, i.e. at T_g = 600 C. Furthermore, for all T_g, Al-doped films have a higher doping efficiency than the Ga-doped counterparts. In order to look deeper into the microscopic origin of this behavior, the samples were post-annealed in vacuum at 400 C. Experimental results showed that the free charge carrier density of Al-doped samples first decreased and saturated afterward with increasing annealing time. On the other hand, the free charge carrier density of the Ga-doped samples first slightly increased and saturated with increasing annealing time. For both doping series, the saturation value of n ~ 1 x 10^20 cm^-3 was very close to the data that has been observed for (i) high temperature grown samples and (ii) the solubility limit of Al in ZnO of 0.3 at.% = 1.2x 10^20 cm^-3, that has been determined by Shirouzu et al. for high temperature grown (T_g > 600 C) Al-doped ZnO [9]. Correspondingly, the optical bandgap also changed, i.e. increased (decreased) for Al- (Ga-) doping series, and approached a constant value of 3.5 0 +- 0.1 eV which is explained by generation of acceptor-like compensating defects, and the solubility limit of the dopants. From XRD data, no secondary phases were found for as-grown and post-annealed films. However, the slight improvement of crystalline quality has been observed on post-annealed samples. Further, it has been shown that the growth and annealing temperatures are important as they strongly affect the metastable state of the solid solution that samples grown at low temperature represent. The low solubility limit of the dopants, i.e. 0.3 at.% for Al in ZnO under equilibrium condition, can be increased by preparing samples by non-equilibrium growth techniques [10]. This is also consistent with experimental results of this work that Al- as well as Ga-doped metastable ZnO and (Mg,Zn)O thin films can be prepared with highest possible doping efficiency for the dopant concentration up to 2.5 at.% when growth or annealing temperatures below 400 C are used.

O protótipo de um detector de nêutrons térmicos portátil foi desenvolvido no Instituto de Pesquisa Energéticas e Nucleares (IPEN-CNEN/SP), utilizando um fotodiodo de Si do tipo PIN associado a um filme de boro enriquecido. O filme de boro foi fabricado por meio da técnica de Deposição a Laser Pulsado, considerando duas possibilidades para depositar o boro: deposição direta do boro na face do fotodiodo e deposição na lâmina de vidro. Foram desenvolvidos dois protótipos, no primeiro foi possível ler apenas o sinal elétrico do sistema fotodiodo-boro no qual o filme está depositado na lâmina de vidro. Para aprimorar a resposta do sistema de detecção, outro circuito foi desenvolvido e permitiu contar nêutrons em ambas as situações tanto do filme na lamínula quanto do filme direto no fotodiodo. A caracterização dos protótipos foi feita via irradiação de feixes de nêutrons predominantemente térmicos e frios, por meio de quatro experimentos principais: reposta do sistema ao fluxo de nêutrons, teste de linearidade, resposta angular e o teste de reprodutibilidade. Os protótipos apresentaram uma resposta linear à variação do fluxo, reprodutibilidade, e a resposta angular não foi isotrópica. A eficiência intrínseca em porcentagem do protótipo 1 para um espectro de nêutrons predominantemente térmicos e frios foi (1,17 &plusmn; 0,01) % e (1,37 &plusmn; 0,01) %, respectivamente. No protótipo 2 foram feitas medições de nêutrons com os dois sistemas fotodiodo-boro (lâmina de vidro, direto no fotodiodo), porém nas medidas com o boro direto no sensor houve um aumento significativo no ruído eletrônico. A eficiência intrínseca do protótipo 2 para os nêutrons frios foi de (5,2 &plusmn; 0,4) %. / A portable thermal neutron detector prototype, using a silicon photodiode type PIN coupled to a boron converter, was developed at Nuclear and Energy Research Institute (IPEN-CNEN/SP). The boron layers were made by Pulsed Laser Deposition method using two configurations: directly deposited on the surface of photodiode and at a glass surface. Two prototypes were made in this study using two different associated electronics, in the first prototype is only possible reads signs from the photodiode coupled to boron film and in the second one reads both types of configurations (directly on the photodiode, boron glass). The prototypes were characterized using thermal and cold neutron beam. Four experiments were performed: response of the detection system at neutron beam, linearity test, angular response and repetitive test. The prototypes present a linear behavior, were reproducible and the angular response of the prototypes was not isotropic. The values of intrinsic efficiency from the prototype 1 for thermal and cold neutron were respectively: (1.17 &plusmn; 0.01) % e (1.37 &plusmn; 0.01) %. In the prototype 2 it was performed an experiment for compare the read out in the detection system for the two possible configuration of system photodiode-boron, in the situation that the boron is part integrant of the system there was an significant increase in the electronic noise, therefore the characterization of this prototype were made using the boron film coupled to the photodiode, and intrinsic efficiency for cold neutron beam was (5.2 &plusmn; 0.4) %.