System on Chip (SoC) and System in Package (SiP) are two electronic technologies that involve integrating multiple functionalities onto a single platform. When the platform is a single wafer, as in SOC, it requires the ability to deposit various materials that enable the different functions on to an underlying substrate that can host the electronic circuitry. Transition metal oxides which have a wide range of properties are ideal candidates for the functional material. Si wafer on which micro-electronics technology is widely commercialized is the ideal host platform. Integrating oxides with Si, generally in the form of thin films as required by microelectronics technology, is however a challenge. It starts with the fact that the properties of crystalline oxides to be exploited in performing various functions are direction dependent. Thus, thin films of these oxides need to be deposited on Si in certain crystallographic orientations. Even if a suitably oriented Si wafer surface were available, it does not always provide for epitaxial growth a critical requirement for controlling the crystalline orientation of thin films. This is because Si surface is covered by an amorphous oxide of Si (SiOx). Thus, during growth of the functional oxide, an ambience in which the Si itself will not oxidize needs to be provided. In addition, during thin film growth on either Si or SiOx surface stresses are generated from various sources. Stress and its relaxation are also associated with the formation and evolution of defects. Both, stress and defects need to be managed in order to harness their beneficial effects and prevent detrimental ones. Given the requirement of SoC technology and the problem associated, the research work reported in this thesis was hence concerned with the precise controlling the stress and microstructure in oxide thin films deposited on Si substrates. In order to do so a versatile, ultra high vacuum (UHV) thin film with a base pressure of 10-9 Torr was designed and built as part of this study. The chamber is capable of depositing films by both sputtering (RF & DC) and pulsed laser ablation (PLD). The system has been designed to include an optical curvature measurement tool that enabled real-time stress measurement during growth. Doped zirconia, ZrO2, was chosen as the first oxide to be deposited, as it is among the few oxides that is more stable than SiOx. It is hence used as a buffer layer. It is shown in this thesis that a change in the growth rate at nucleation can lead to (100) or (111) textured films. These two are among the most commonly preferred orientation. Following nucleation a change in growth rate does not affect orientation but affects stress. Thus, independent selection of texture and stress is demonstrated in YSZ thin films on Si. A quantitative model based on the adatom motion on the growth surface and the anisotropic growth rates of the two orientations is used to explain these observations. This study was then subsequent extended to the growth on platinized Si another commonly used Si platform.. A knowledge of the stress and microstructure tailoring in cubic zirconia on Si was then extended to look at the effect of stress on electrical properties of zirconia on germanium for high-k dielectric applications. Ge channels are expected to play a key role in next generation n-MOS technology. Development of high-k dielectrics for channel control is hence essential. Interesting stress and property relations were analyzed in ZrO2/Ge. Stress and texture in pulsed laser deposited (PLD) oxides on silicon and SrTiO3 were studied. It is shown in this thesis that stress tuning is critical to achieve the highest possible dielectric constant. The effect of stress on dielectric constant is due to two reasons. The first one is an indirect effect involving the effect of stress on phase stability. The second one is the direct effect involving interatomic distance. By stress control an equivalent oxide thickness (EOT) of 0.8 nm was achieved in sputter deposited ZrO2/Ge films at 5 nm thickness. This is among the best reported till date. Finally, the effect of growth parameters and deposition geometry on the microstructural and stress evolution during deposition of SrTiO3 on Si and BaTiO3 on SrTiO3 by pulsed laser deposition is the same chamber is described.

Metal Oxide (MO)semiconductors are one of the most widely used materials in commercial gas sensor devices. The basic principle of chemoresistive gas sensor operation stems on the high sensitivity of electrical resistance to ambient gaseous conditions. Depending on whether the oxide is "p type" or "n type", the resistance increases (or decrease), when placed in atmosphere containing reducing (or oxidizing) gases. The study of conductometric metal oxide semiconductor gas sensors has dual importance in view of their technological device applications and understanding fundamental MO-gas interactions. Metal oxides based sensors offer high thermal, mechanical and chemical stability. A large number of MOs show good sensitivities to various gases like CO, NOX, SOX, NH3, alcohols and other Volatile Organic Compounds (VOCs). VOCs are very common hazardous pollutants in the environment. Gas sensors are in great demand for their various applications such as food quality control, fermentation industries, road safety, defence, environmental monitoring and other chemical industries. The aim of the study is to explore the possibility of advancements in semiconducting MO based gas sensor devices through tuning microstructural parameters along with chemical dopants or additives. And further to investigate the underlying mechanism of conductometric MO gas sensors. The novel synthesis method employed is based on the solution combustion method coupled with ultrasonically nebulized spray pyrolysis technique. The well studied SnO2 and relatively unexplored Cr2O3 oxide systems are selected for the study. The non-equilibrium processing conditions result in unique microstructure and defect chemistry. In addition, using this technique MO - Reduced Graphene Oxide (RGO) nanocomposite films has also been fabricated and its application to room temperature gas sensor devices is demonstrated. The thesis comprises of seven chapters. the following section describe the summery of individual chapters. The Chapter 1 describes the introduction and background literature of this technology. A brief review of developments in gas sensor technology so far has been enlisted. This chapter also gives a glimpse of applications of MO semiconductors based sensors. The underlying mechanism involved in the sensing reaction and the primary factors influencing the response of a gas sensor device are enlisted. Further in the later part of the chapter focused the material selection criteria, effect of additives/dopants and future prospects of the technology. The end of this chapter highlights the objective and scope of the work in this dissertation. In the Chapter 2 the the materials selection, characterization techniques and particularly the experimental setups used are elaborated. This includes the deposition method used, which is developed in our group and the the in house built gas sensing system including its working principles and various issues have been addressed. The Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) is a novel deposition method devised, which is a combination of conventional spray pyrolysis and solution combustion technique. Spray pyrolysis is versatile, economic and simple technique, which can be used for large area deposition of porous films. The intention is to exploit the exothermicity of combustion reaction in order to have high crystallinity, smaller crystallite size with high surface area, which are extremely important in gas sensor design and its efficiency. Further the gas sensing system and its operation are discussed in detail including the advantages of vertical sensing chamber geometry, wider analyte concentration range (ppm to percentage) obtained through vapor pressure data and simultaneous multi sensor characterization allowing better comparison. Here in this work, Chromium oxide (Cr2O3) and Tin oxide (SnO2) are selected as gas sensing materials for this work as a p-type and n-type metal oxide semiconductors respectively. Nevertheless Cr2O3 is a less explored gas sensing material as compared to SnO2, which is also being used in many commercially available gas sensor devices. Thus, studying and comparing gas sensing properties of a relatively novel and a well established material would justify the potential of the novel deposition technique developed. In Chapter 3, the effect of exothermic reaction between oxidizer and fuel, on the morphology, surface stoichiometry and observed gas sensing properties of Cr2O3 thin films deposited by UNSPACM, is studied. An elaborative study on the structural, morphological and surface stoichiometry of chromium oxide films is undertaken. Various deposition parameters have been optimized. An extensive and systematic gas sensing study is carried out on Cr2O3 films deposited, to achieve unique microstructure. The crystallinity and microstructure are investigated by varying the deposition conditions. Further, the effect of annealing in oxygen gas atmospheres on the films was also investigated. The gas sensing properties are studied for various VOCs, in temperature range 200 - 375 oC. The possible sensing mechanism and surface chemical processes involved in ethanol sensing, based on empirical results, are discussed. In chapter 4, the effect of 1% Pt doping on gas sensing properties of Cr2O3 thin films prepared by UNSPACM, is investigated. The chemical analysis is done using x-ray photoelectron spectroscopy to find the chemical state of Pt and quantification is done. The gas sensing is done towards gases like NO2, Methane and Ethanol. The enhancement in sensitivity and remarkable reduction in response as well as recovery times have been modeled with kinetic response analysis to study the variation with temperature as well as concentration. Further the analysis of observations and model fittings is discussed. The Chapter 5 deals with the defects induced ferromagnetism and gas sensing studies SnO2 nanoparticles prepared by solution combustion method. The structural, chemical analysis of as-synthesized and annealed SnO2 nanoparticles reveal gradual reduction in defect concentration of as-prepared SnO2. The findings of various characterization techniques along with optical absorption and magnetic studies to investigate the defect structure of the material are presented. As defects play crucial role in gas sensing properties of the metal oxide material, the defect induced room temperature ferromagnetism in undoped SnO2 has been used as a potential tool to probe the evidence of the defects. Finally a correlation is established between observed room temperature ferromagnetism and gas sensing studies and primary role of defects in gas sensing mechanism over microstructure is realized . The Chapter 6 presents the deposition of SnO2 thin films by UNSPACM method on glass substrates for gas sensing application. The readiness of UNSPACM in making sensor materials with unform dopant distribution is demonstrated in order to improve the sensor performance in terms of response and selectivity. The chemical composition, film morphology and gas sensing studies are reported. The SnO2 is doped with Cr and Pt to enhance the sensing properties of the material. The doped Oxide films are found to show enhancement in sensitivity and improve the selectivity of the films towards specific gases like NO2 and CO. Further in Chapter 7 an effort has been made to overcome the problem of high operating temperature of metal oxide gas sensors through use of Reduced Graphene Oxide (RGO) and metal oxide nanocomposite films. Although RGO shows room temperature response towards many toxic and hazardous gases but it exhibits poor sensor signal recovery. This has been successfully solved by making nanohybrids of RGO and SnO2. It not only improves the sensor signal kinetics but it enhances the sensitivity also. Thus this chapter endeavors towards low power consumption gas sensing devices. The key findings and future aspects are summarized in the Chapter 8.

Die vorliegende Arbeit befasst sich mit der Untersuchung von Schottky-Kontakten auf halbleitenden Zinkoxid- und β-Galliumoxid-Dünnfilmen. Nach einer kurzen Einführung in die verwendeten Materialsysteme und die Theorie von Schottky-Kontakten werden die Eigenschaften von verschiedenartig hergestellten Schottky-Kontakten auf Zinkoxid aufgezeigt. Dazu werden typischerweise Strom-Spannungs- und Kapazitäts-Spannungs-Messungen genutzt. Für die Zinkoxid-basierten Schottky-Kontakte konnte anhand verschiedenartig hergestellter Schottky-Kontakte gezeigt werden, dass deren Barrierenformation maßgeblich von Sauerstoffvakanzen nahe der Metall-Halbleiter-Grenzfläche beeinflusst wird. Zur Realisierung von Galliumoxid-basierten Schottky-Kontakten wurden zunächst die Eigenschaften von undotierten und Silizium-dotierten Galliumoxid-Dünnfilmen untersucht. Diese Dünnfilme sind mittels gepulster Laserabscheidung auf c-plane Saphir hergestellt. Als Prozessparameter sind in dieser Arbeit die Wachstumstemperatur, der Sauerstoffpartialdruck in der Kammer und der Silizumgehalt bspw. in Bezug auf Leitfähigkeit, Oberflächenmorphologie oder Kristallinität zur Realisierung von Schottky-Kontakten optimiert. Auf diesen Dünnfilmen wurden mit verschiedenen Herstellungsverfahren, wie thermischer Verdampfung, (reaktiver) Kathodenzerstäubung oder (reaktiver) Distanz-Kathodenzerstäubung, Metall- bzw. Metalloxid-Schottky-Kontakte aufgebracht. Dabei werden unter anderem die elektrischen Eigenschaften direkt nach der Herstellung und deren Entwicklung im weiteren zeitlichen Verlauf untersucht. Des Weiteren werden die Temperaturstabilität oder aber die Spannungsstabilität der Schottky-Kontakte studiert. Ein Vergleich zu Schottky-Kontakten auf β-Galliumoxid-Volumenmaterial wird anhand mittels reaktiver Distanz-Kathodenzerstäubung hergestellter Platinoxid-Dioden durchgeführt.

Surface texturization of Transparent Conductive Oxides (TCOs) is a well-known strategy to enhance the light-trapping capabilities of thin-film solar cells and thus, to increase their power conversion efficiency. Herein, the surface modification of fluorine-doped tin oxide (FTO) using picosecond infrared direct laser interference patterning (DLIP) is presented. The surface characterization exhibits periodic microchannels, which act as diffraction gratings yielding an increase in the average diffuse transmittance up to 870% in the spectral range of 400–1000 nm. Despite the one dimensionality of the microstructures, the films did not acquire a significant anisotropic electrical behavior, but a partial deterioration of their conductivity is observed as a result of the removal of conductive material. This work proposes the feasibility of trading off a portion of the electrical conductivity to obtain a substantial improvement in the optical performance.

In der vorliegenden Arbeit wurde mit Hilfe eines Photon-STM die Korrelation zwischen optischen Eigenschaften und der lokalen Morphologie an zwei unterschiedlichen Systemen untersucht. Hierfür wurden zum einem oxidgetragene Ensemble von Silber-Partikeln präpariert, wobei sowohl die Partikelform (Kuppel- und Scheibenform) als auch die deponierte Partikeldichte variiert werden konnte. Neben der Präparation solcher Partikel auf Al10O13/NiAl, konnten sphärische Silber-Kolloide geordnet, als auch ungeordnet auf HOPG aufgebracht und untersucht werden. Dabei zeigte sich, dass das Verhältnis von Höhen zu Breiten nicht nur einen signifikanten Einfluss auf die Mie-Resonanz des einzelnen Partikels hat, sondern auch die elektromagnetische Kopplung der Partikel in einem Ensemble stark kontrolliert. Die energetische Lage der Mie-Resonanz zeigt im Fall der kuppelförmigen Ag-Partikel eine starke Abhängigkeit vom Intepartikel-Abstand, was sich in einer Verschiebung zu höheren Energien für eine steigende Partikeldichte äußert. Eine solche Abhängigkeit konnte bei den Ensembles der scheibenförmigen Partikel nicht beobachtet werden. Des weiteren zeigte sich, dass, verglichen mit den ungeordneten Ensembles, die selbstorganisierte langreichweitige Ordnung der Silber-Kolloide auf HOPG nur einen schwachen Einfluss auf die energetische Position der Mie Resonanz hat.Das zweite hier untersuchte System sind dünne MgO Filme unterschiedlicher Dicken auf einem Mo(001) Substrat. Diese zeigen ein reichhaltiges Wachstumsverhalten, welches durch eine Differenz in den Gitterkonstanten von 5.3% begründet ist und erst ab etwa 25 ML zu einem flachen und defektarmen Film führt. Die so induzierte Spannung relaxiert bis zu einer Dicke von etwa 7 ML in einer periodischen Überstruktur die aus abwechselnd flachen und verkippten Ebenen an der MgO-Mo Grenzschicht hervorgeht. Für MgO Filme mit einer Dicke von etwa 12 ML werden dann Schraubenversetzungen, ausgedehnte verkippte Ebenen und Stufenkanten mit einer Orientierung entlang der Richtung beobachtet. Die optische Charakterisierung durch Feldemission von Elektronen aus der STM-Spitze in den MgO-Film wird dominiert von zwei Emissionsmaxima bei Energien von 3.1 eV und 4.4 eV. Die kontrollierte Nukleation von Gold Partikeln und die Erzeugung von Farbzentren im MgO Film erlaubten eine Zuordnung dieser Emissionen zu strahlenden Zerfällen von Exitonen an Ecken, Kinken bzw. Stufen des Magnesiumoxids. Solche Emissionsprozesse konnten allerdings nur unter Einstellungen beobachtet werden, bei denen ein gleichzeitiges Rastern der Oberfläche unmöglich ist. Bei moderaten Einstellungen war auch eine ortsaufgelösten Spektroskopie möglich, wobei dann neue Emissionsmechanismen beobachtet wurden. Dabei sind zwei Prozesse wesentlich; zum einen die Ausbildung von sog. Spitzen-induzierten Plasmonen im Bereich zwischen Spitze und dem Mo-Substrat, zum anderen strahlende Elektronenübergänge zwischen sog. Feldemissionsresonanzen, die sich im Spitze/MgO-Film System ausbilden. / In this thesis, the correlation between the optical properties and the local morphology of supported silver nanoparticle ensembles and MgO thin films deposited on Mo(001) systems is explored by means of Photon-STM. In the first section, dome and disk shaped Ag nanoparticle ensembles with increasing density on an alumina film on NiAl(110) were analyzed as well as ordered and disordered ensembles of Ag nanocolloids on HOPG. The aspect ratio of the Ag nanoparticles was found to have a significant influence not only on the Mie plasmon resonance of a single particle, but also on the electromagnetic coupling within the nanoparticle ensembles. The Mie resonance in the ensemble of dome shaped Ag nanoparticles shows a strong dependence on the interparticle distance, where it shifts to higher energies with increasing particle density, due to destructive interference effects. In the disk-like Ag ensembles, however, the plasmon energy is independent of particle-particle separation. The long-range lateral ordering of size-selected Ag nanocolloids is found to induce a high dipole-dipole coupling within the ensemble. This is mainly reflected by the enhancement of the spectral intensity of the in-plane Mie mode, due to constructive coupling. However, ensembles with either well-ordered or disordered arrangements reveal no important difference in their optical properties, reflecting the weak influence of the long-range order in the particle ensemble. Thin MgO films with different thicknesses were grown on a Mo(001) surface. The stress resulting from the 5.3% lattice mismatch between the MgO(001) and the Mo(001) lattice parameters is found to control the surface morphology of the MgO film until thicknesses of around 25ML at which flat and defect-poor films are obtained. The relaxation of the stress induces a periodic network in the first 7ML of the MgO film, consisting of alternated flat and tilted mosaics. The presence of screw dislocations, steps oriented along the MgO directions, and tilted planes is observed when the MgO films are approximately 12ML thick. In addition, an increase of the MgO work function around these new surface features is revealed from STM spectroscopy. The photon emission induced by field-emitted electron injection from the STM tip into the MgO films is dominated by two emission bands located at 3.1eV and 4.4eV. To check the origin of these bands, further experiments, namely, nucleation of Au particles and creation of F-centers on the MgO surface, have been performed. The nucleation of Au particles at the low coordinated sites is found to quench the MgO optical signal, while the creation or annihilation of F-centers does not alter the MgO emission bands. The 3.1eV and the 4.4eV bands are therefore assigned to the radiative decay of MgO excitons at corner and kink sites, and step sites, respectively. Besides, spatially resolved optical measurements in the tunneling mode of the STM revealed different light emission mechanisms. These radiative processes are mainly related to tip-induced plasmons that form between the tip and the Mo support and to electron transitions between field-emission-resonance states in the STM tip-MgO film junction. The signal from exciton decays at corners and kinks of the MgO surface is however only observed at excitation conditions where the spatial resolution is already strongly reduced.

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