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Radiation tolerance is determined as an ability of crystalline materials to withstand the accumulation of the radiation induced disorder. Based on the magnitudes of such disorder levels, semiconductors are commonly grouped into the low- or high-radiation tolerant. Nevertheless, upon exposing to sufficiently high fluences, in all cases known by far, it ends up with either extremely high disorder levels or amorphization. Here we show that gamma/beta double polymorph Ga2O3 structures exhibit unprecedently high radiation tolerance. Specifically, for room temperature experiments, they tolerate a disorder equivalent to hundreds of displacements per atom, without severe degradations of crystallinity; in comparison with, e.g., Si amorphizable already with the lattice atoms displaced just once. We explain this behavior by an interesting combination of the Ga- and O-sublattice properties in gamma-Ga2O3. In particular, O-sublattice exhibits a strong recrystallization trend to recover the face-centered-cubic stacking despite high mobility of O atoms in collision cascades compared to Ga. Concurrently, the characteristic structure of the Ga-sublattice is nearly insensitive to the accumulated disorder. Jointly it explains macroscopically negligible structural deformations in gamma-Ga2O3 observed in experiment. Notably, we also explained the origin of the beta-to-gamma Ga2O3 transformation, as a function of increased disorder in beta-Ga2O3 and studied the phenomena as a function of the chemical nature of the implanted atoms. As a result, we conclude that gamma-beta double polymorph Ga2O3 structures, in terms of their radiation tolerance properties, benchmark a new class of universal radiation tolerant semiconductors.

EBSD data and irradiation parameters

Interest in the synthesis and fabrication of gallium oxide (Ga2O3) nanostructures as wide bandgap semiconductor-based ultraviolet (UV) photodetectors has recently increased due to their importance in cases of deep-UV photodetectors operating in high power/temperature conditions. Due to their unique properties, i.e., higher surface-to-volume ratio and quantum effects, these nanostructures can significantly enhance the sensitivity of detection. In this work, two Ga2O3 nanostructured films with different nanowire densities and sizes obtained by thermal oxidation of Ga on quartz, in the presence and absence of Ag catalyst, were investigated. The electrical properties influenced by the density of Ga2O3 nanowires (NWs) were analyzed to define the configuration of UV detection. The electrical measurements were performed on two different electric contacts and were located at distances of 1 and 3 mm. Factors affecting the detection performance of Ga2O3 NWs film, such as the distance between metal contacts (1 and 3 mm apart), voltages (5-20 V) and transient photocurrents were discussed in relation to the composition and nanostructure of the Ga2O3 NWs film.

Currently, a significant portion (~50%) of global warming emissions, such as CO, are related to energy production and transportation. As most energy usage will be electrical (as well as transportation), the efficient management of electrical power is thus central to achieve the XXI century climatic goals. Ultra‐wide bandgap (UWBG) semiconductors are at the very frontier of electronics for energy management or energy electronics. A new generation of UWBG semiconductors will open new territories for higher power rated power electronics and solar‐blind deeper ultraviolet optoelectronics. Gallium oxide—GaO (4.5–4.9 eV), has recently emerged pushing the limits set by more conventional WBG (~3 eV) materials, such as SiC and GaN, as well as for transparent conducting oxides (TCO), such asInO, ZnO and SnO, to name a few. Indeed, GaO as the first oxide used as a semiconductor for power electronics, has sparked an interest in oxide semiconductors to be investigated (oxides represent the largest family of UWBG). Among these new power electronic materials, AlxGa1‐xO may provide high‐power heterostructure electronic and photonic devices at bandgaps far beyond all materials available today (~8 eV) or ZnGaO (~5 eV), enabling spinel bipolar energy electronics for the first time ever. Here, we review the state‐of‐the‐art and prospects of some ultra‐wide bandgap oxide semiconductor arising technologies as promising innovative material solutions towards a sustainable zero emission society.

The influence of Al2O3 as an additive and the heat-treatment regime on the luminescence spectra of gallate glass-ceramics was investigated. It is shown that its luminescence efficiency can be enhanced by changing the submicron-inhomogeneous structure of the initial glasses.

Um neue Halbleiter-Bauelemente zu entwickeln und die Effizienz bereits existierender zu verbessern, müssen neue Materialien erkundet und untersucht werden. Für Anwendungen in Hochleistungselektronik und UV-Optoelektronik ist Ga2O3 mit seiner ultra-weiten Bandlücke von 4.8 eV ein vielversprechender Kandidat. Diese Anwendung haben zu wachsendem Interesse an seinen fundamentalen elektronischen und optischen Eigenschaften geführt. Diese Dissertation präsentiert eine umfassende ab initio-Untersuchung der elektronischen Anregungen in Ga2O3, um zu dem Verständnis dieser fundamentalen Eigenschaften beizutragen. Die Arbeit besteht aus zwei Teilen: Im ersten Teil präsentieren wir eine Vielteilchen-Störungstheorie Methode zur konsistenten Berechnung der neutralen Anregungen von Valenz- und Kernelektronen in kristallinen Halbleitern. Diese ermöglicht die präzise Berechnung von Absorptions- und Streuungsspektren vom optischen bis zum Röntgenbereich. Zusätzlich präsentieren wir einen neuartigen Ausdruck für resonante inelastische Röntgenstreuung (RIXS) innerhalb unseres Vielteilchen-Formalismus, der eine detaillierte Analyse dieser Streuung erlaubt. Mit ausgewählten Beispielen demonstrieren wir das Potential unserer Implementation, die Spektren dieser verschiedenen spektroskopischen Methoden zu berechnen, zu analysieren und zu interpretieren. Im zweiten Teil der Dissertation verwenden wir unsere Methode, um die Anregungen der Valenzelektronen, sowie der Ga 1s-, Ga 2p- und O 1s-Elektronen in Ga2O3 zu berechnen. Wir finden ausgeprägte Unterschiede in den diversen Röntgenabsorptionsspektren von Ga2O3 -Polymorphen, die von der unterschiedlichen lokalen elektronischen Struktur stammen. Wir bestimmen die Zusammensetzung der Valenz- und Kernanregungen und analysieren ihre Signatur in den verschiedenen Absorptions- und Streuungsspektren. Abschließend demonstrieren wir wie RIXS einen zusätzlichen Blickwinkel auf die Valenz- und Kernanregungen und deren Wechselwirkungen ermöglicht., To develop new semiconductor devices and improve the performance of existing ones, the exploration and understanding of novel materials is required. With an ultra-wide band gap of around 4.8 eV, Ga2O3 is a promising candidate for applications in UV-optoelectronics and power electronics. These applications have led to an increasing interest in its fundamental electronic and optical properties. In this thesis, we present a comprehensive first-principles study of the electronic excitations of Ga2O3 to contribute to the understanding of these fundamental properties. The thesis consists of two parts: In the first part, we present an all-electron many-body perturbation theory (MBPT) approach for consistent calculations of neutral core and valence excitations. It enables accurate calculation of absorption and inelastic scattering spectra in the optical, UV, and x-ray region. While these spectroscopic techniques probe either the valence or core excitations, resonant inelastic x-ray scattering (RIXS) reveals the interplay between the two. We present a novel expression for the RIXS cross section within our all-electron many-body formalism that allows for a detailed analysis of this interplay. We demonstrate the capability of our implementation to compute, analyze, and interpret the different spectroscopic techniques with selected examples of prototypical insulators. In the second part, we apply our approach to study valence excitations, as well as excitations of various core states, i.e. the gallium 1s, gallium 2p, and oxygen 1s states in Ga2O3 . Comparing the core spectra of Ga2O3 polymorphs, we find distinct differences that originate from their local environments. We determine the composition of valence and core excitons, and analyze their signatures in the various absorption and scattering spectra. Finally, we demonstrate how RIXS can be employed to provide a different viewpoint on the core and valence excitations and unravel the interplay between them.

A new type of photocatalyst is proposed on the basis of aero-beta-Ga2O3, which is a material constructed from a network of interconnected tetrapods with arms in the form of microtubes with nanometric walls. The aero-Ga2O3 material is obtained by annealing of aero-GaN fabricated by epitaxial growth on ZnO microtetrapods. The hybrid structures composed of aero-Ga2O3 functionalized with Au or Pt nanodots were tested for the photocatalytic degradation of methylene blue dye under UV or visible light illumination. The functionalization of aero-Ga2O3 with noble metals results in the enhancement of the photocatalytic performances of bare material, reaching the performances inherent to ZnO while gaining the advantage of the increased chemical stability. The mechanisms of enhancement of the photocatalytic properties by activating aero-Ga2O3 with noble metals are discussed to elucidate their potential for environmental applications., QC 20210524

The transition from insulator to conductor can be realized in some materials but requires modification of both the arrangement of atoms and their electronic configurations. This is often achieved by doping. Here we reveal a different mechanism the lattice may adopt to induce such a transition. Experiments showed the surprising finding that limited exposure to sub-bandgap light caused a permanent transition from an insulator state to a conductor state in the insulating oxide Ga2O3, with 9-orders of magnitude increase in electronic conduction. Furthermore, annealing up to 400 C did not suppress or decrease the induced conductivity. Photoexcitation by light-induced modification in the charge state of defects and subsequent lattice distortion around them was suggested to be the underlying mechanism behind this transition. Density functional theory calculations confirmed that modifying the charge state of defects leads to redistribution of the localized electrons and massive structural distortion in the surrounding lattice, causing large shifts in the density of states and introducing new states with shallower energy levels. Both experimental and theoretical results revealed the introduction of new stable shallow energy levels, explaining the mechanism behind the transition from an insulator to a conductor state by light. We suggest that this mechanism may occur in other wide bandgap metal oxides leading to drastic modification in their electronic properties.

Um neue Halbleiter-Bauelemente zu entwickeln und die Effizienz bereits existierender zu verbessern, müssen neue Materialien erkundet und untersucht werden. Für Anwendungen in Hochleistungselektronik und UV-Optoelektronik ist Ga2O3 mit seiner ultra-weiten Bandlücke von 4.8 eV ein vielversprechender Kandidat. Diese Anwendung haben zu wachsendem Interesse an seinen fundamentalen elektronischen und optischen Eigenschaften geführt. Diese Dissertation präsentiert eine umfassende ab initio-Untersuchung der elektronischen Anregungen in Ga2O3, um zu dem Verständnis dieser fundamentalen Eigenschaften beizutragen. Die Arbeit besteht aus zwei Teilen: Im ersten Teil präsentieren wir eine Vielteilchen-Störungstheorie Methode zur konsistenten Berechnung der neutralen Anregungen von Valenz- und Kernelektronen in kristallinen Halbleitern. Diese ermöglicht die präzise Berechnung von Absorptions- und Streuungsspektren vom optischen bis zum Röntgenbereich. Zusätzlich präsentieren wir einen neuartigen Ausdruck für resonante inelastische Röntgenstreuung (RIXS) innerhalb unseres Vielteilchen-Formalismus, der eine detaillierte Analyse dieser Streuung erlaubt. Mit ausgewählten Beispielen demonstrieren wir das Potential unserer Implementation, die Spektren dieser verschiedenen spektroskopischen Methoden zu berechnen, zu analysieren und zu interpretieren. Im zweiten Teil der Dissertation verwenden wir unsere Methode, um die Anregungen der Valenzelektronen, sowie der Ga 1s-, Ga 2p- und O 1s-Elektronen in Ga2O3 zu berechnen. Wir finden ausgeprägte Unterschiede in den diversen Röntgenabsorptionsspektren von Ga2O3 -Polymorphen, die von der unterschiedlichen lokalen elektronischen Struktur stammen. Wir bestimmen die Zusammensetzung der Valenz- und Kernanregungen und analysieren ihre Signatur in den verschiedenen Absorptions- und Streuungsspektren. Abschließend demonstrieren wir wie RIXS einen zusätzlichen Blickwinkel auf die Valenz- und Kernanregungen und deren Wechselwirkungen ermöglicht., To develop new semiconductor devices and improve the performance of existing ones, the exploration and understanding of novel materials is required. With an ultra-wide band gap of around 4.8 eV, Ga2O3 is a promising candidate for applications in UV-optoelectronics and power electronics. These applications have led to an increasing interest in its fundamental electronic and optical properties. In this thesis, we present a comprehensive first-principles study of the electronic excitations of Ga2O3 to contribute to the understanding of these fundamental properties. The thesis consists of two parts: In the first part, we present an all-electron many-body perturbation theory (MBPT) approach for consistent calculations of neutral core and valence excitations. It enables accurate calculation of absorption and inelastic scattering spectra in the optical, UV, and x-ray region. While these spectroscopic techniques probe either the valence or core excitations, resonant inelastic x-ray scattering (RIXS) reveals the interplay between the two. We present a novel expression for the RIXS cross section within our all-electron many-body formalism that allows for a detailed analysis of this interplay. We demonstrate the capability of our implementation to compute, analyze, and interpret the different spectroscopic techniques with selected examples of prototypical insulators. In the second part, we apply our approach to study valence excitations, as well as excitations of various core states, i.e. the gallium 1s, gallium 2p, and oxygen 1s states in Ga2O3 . Comparing the core spectra of Ga2O3 polymorphs, we find distinct differences that originate from their local environments. We determine the composition of valence and core excitons, and analyze their signatures in the various absorption and scattering spectra. Finally, we demonstrate how RIXS can be employed to provide a different viewpoint on the core and valence excitations and unravel the interplay between them.

The influence of Al2O3 as an additive and the heat-treatment regime on the luminescence spectra of gallate glass-ceramics was investigated. It is shown that its luminescence efficiency can be enhanced by changing the submicron-inhomogeneous structure of the initial glasses.

MOSFET power device with beta-Ga2O3substrate are simulated via TCAD and discussed in this paper. Material models are established and calibrated based on the existing experimental results. Device design specifications like channel doping profile, gate-source distance, selective doping, field plate enhancement, and ion-implantation profile are evaluated and discussed. The results serve as a guide and reference for the beta-Ga2O3, MOSFET device design.

MOSFET power device with beta-Ga2O3substrate are simulated via TCAD and discussed in this paper. Material models are established and calibrated based on the existing experimental results. Device design specifications like channel doping profile, gate-source distance, selective doping, field plate enhancement, and ion-implantation profile are evaluated and discussed. The results serve as a guide and reference for the beta-Ga2O3, MOSFET device design.

Gallium oxide (Ga2O3) is a new wide bandgap semiconductor with remarkable properties that offers strong potential for applications in power electronics, optoelectronics, and devices for extreme conditions. In this work, we explore the morphology of Ga2O3 nanostructures on different substrates and temperatures. We used silver catalysts to enhance the growth of Ga2O3 nanowires on substrates such as p-Si substrate doped with boron, 250 nm SiO2 on n-Si, 250 nm Si3N4 on p-Si, quartz, and n-Si substrates by using a thermal oxidation technique at high temperatures (~1000 °C) in the presence of liquid silver paste that served as a catalyst layer. We present the results of the morphological, structural, and elemental characterization of the Ga2O3 nanostructures. This work offers in-depth explanation of the dense, thin, and long Ga2O3 nanowire growth directly on the surfaces of various types of substrates using silver catalysts.

MOSFET power device with beta-Ga2O3substrate are simulated via TCAD and discussed in this paper. Material models are established and calibrated based on the existing experimental results. Device design specifications like channel doping profile, gate-source distance, selective doping, field plate enhancement, and ion-implantation profile are evaluated and discussed. The results serve as a guide and reference for the beta-Ga2O3, MOSFET device design.

In dieser Arbeit werden die grundlegenden Wachstumsprozesse von Ga2O3 , mittels Transmissionselektronenmikroskopie analysiert. Dazu gehört die Untersuchung des heteroepitaktischen Wachstums von Galliumoxidschichten welche mittels Molekularstrahlepitaxie (molekular beam epitaxy MBE), der gepulsten Laser Abscheidung (pulsed laser deposition (PLD)) und der metallorganischen Gasphasenepitaxie (metalorganic vapor phase epitaxy (MOVPE)) auf (0001) orientierte Saphir Substraten abgeschieden wurden. Heteroepitaktisches Wachstum von Ga2O3 auf Saphir (0001) erfolgt bis zu einer Dicke von 3 Monolagen pseudomorph als α-Ga2O3 welches durch die Gitterfehlpassung zwischen Galliumoxid und dem Saphire Substrat induzierte Gitterverspannung stabilisiert wir. Weiterhin, im Fokus der Arbeit stehend, wird das homoepitaktische Wachstum von Galliumoxid auf (100) orientierten Galliumoxidsubstraten untersucht. Neben den Besonderheiten des Schichtwachstums, die sich aus den eingesetzten metallorganischen Präkursoren und Sauerstoffquellen ergeben, wird die Schichtstruktur in Abhängigkeit der typischen Wachstumsparameter (Wachstumstemperatur, Wachstumsrate, Kammerdruck und Fehlorientierung des Substrates) analysiert. Dabei wird gezeigt das homoepitaktischen Wachstum auf (100) orientiertem, β-Ga2O3, mittels MOVPE, die kristalline Perfektion der gewachsenen Schichten stark von den verwendeten Präkursoren (Trimethylgallium (TMGa) und Triethylgallium (TEGa) als metallorganische Ausgangsstoffe und H2 O oder purer Sauerstoff als Oxidant) und den chemischen Prozessen an der Oberfläche bestimmt wird. Des Weiteren wird die Entstehung von Zwillingslammelen in abhähngigkeit der Fehlorientierung untersucht. Durch die Einführung von vorbestimmten Fehlorientierungswinkeln der Substrate ist es möglich das Entstehen der Zwillingslamellen zu verhindern, und ein Stufenflusswachstum zu generieren. Durch die Anwendung eines Ratengleichungsansatzes ist es möglich die experimentell beobachteten Dichten an Zwillingsl, In this work we study the basic growth processes of epitaxial Ga2O3 films, by means of transmission electron microscopy. We investigate the heteroepitaxial growth of thin layers Ga2O3 on the (0001) plane of sapphire grown by molecular beam epitaxy (MBE), pulsed laser deposition (PLD) and metal organic vapor phase epitaxy (MOVPE). Furthermore, we will focus on the homoepitaxial growth on the (100) plane by MOVPE. Beside the peculiarities of the layer growth dependence on different metal organic precursors and oxygen sources, we investigate the influence of typical growth parameters (i.e. growth temperature, growth-rate, chamber pressure and miscut angle of the substrate) on the layer morphology. Incase of heteroepitaxial growth of β-Ga2O3 on (0001) plane of sapphire, independent of the growth method, the formation of a 3 monolayer thick α-Ga2O3 layer is observed, which is stabilized through strain, as a result of the lattice mismatch between sapphire and α-Ga2O3. In case of homoepitaxial growth by MOVPE on (100) oriented β-Ga2O3, the crystalline quality of the grown layer strongly depends on the used precursor (tri-methyl-gallium (TMGa) or tri-ethyl-gallium (TEGa) as metal precursor and H2O or pure oxygen as oxidant) and the chemical processes on the surface, respectively. Further on is the crystalline perfection of homoepitaxial layers grown by MOVPE on (100) oriented β-Ga2O3 substrates strongly dependent on the miscut-angle of the substrates. Layer grown on substrate with a small miscut-angle (< 2°) show high amount of twin lamella. These twin lamella are a result of a possible double positioning mechanism of ad-atoms on the growth surface. By introducing appropriate miscut-angles of the substrate it is possible to suppress the formation of these twin lamellae, and enable step flow growth. By applying a rate equation approach, describing the competing processes of incorporation of ad-atoms at kink sites or nucleation and growth of two dimensional island, it is poss

Ga2O3 has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga2O3 power devices stimulated by early demonstrations of high-voltage Ga2O3 field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletionand enhancement-mode Ga2O3 FETs - which have predominantly been lateral devices - for power switching and radiation-hard electronics. The development of vertical Ga2O3 transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed. © 2020 by World Scientific Publishing Co. Pte. Ltd.

Ga2O3 has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga2O3 power devices stimulated by early demonstrations of high-voltage Ga2O3 field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletionand enhancement-mode Ga2O3 FETs-which have predominantly been lateral devices-for power switching and radiation-hard electronics. The development of vertical Ga2O3 transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed. © 2019 World Scientific Publishing Company.

Gallium oxide (Ga2O3) has been gaining considerable attention as a representative of ultra-wide bandgap semiconductors. This paper introduces our state-of-the-art Ga2O3 device technologies developed for applications to future power switching electronics. © 2018 GaAs Mantech Incorporated. All Rights Reserved.

Semiconductor power switches are necessary for the deployment of next-generation electrical systems, including renewable energy generators, electric vehicle drivetrains, and high-power communications systems. Current silicon-based technologies are limited by insufficient blocking voltages due to bandgap limitations and processing-induced defects, undesirably high on-state resistances due to gate charge trapping at poorly understood dielectric/semiconductor interfaces, and limited reliability due to electrical and thermal failure under aggressive operating conditions. As such, new materials and device architectures are required to achieve previously unattained power, efficiency, and reliability. This dissertation identifies and investigates material candidates and demonstrates their incorporation into new device architectures for power switches. Wide bandgap (WBG) semiconductors such as GaN, and ultra-wide bandgap (UWBG) semiconductors such as Ga2O3 and diamond are employed to address the previously stated limitations. Gate charge trapping in these systems is addressed through use of high-k dielectrics not previously employed for WBG and UWBG switches. ZrO2 and HfO2 dielectrics are presented as candidates for dielectric and interface charge tuning on GaN and Ga2O3, thereby allowing the possibility of threshold voltage manipulation and normally-off behavior in WBG and UWBG switches. Fabrication technologies for WBG and UWBG switches are also reported. Normally-on and -off AlGaN/GaN MOS-HEMTs with threshold voltages between -3 to +4 V are demonstrated through a combination of ZrO2 dielectric selection and AlGaN recess etching. Design and processing for normally-off vertical GaN MOSFETs are also developed, with emphasis on critical challenges in fabricating these devices. Additionally, the fabrication and stability of hydrogen-terminated diamond switches with Al2O3 surface transfer dopants are reported. Finally, new materials and processes for improved electrical and th

Byl studován vliv obsahu oxidu gallitého na termické chování a fyzikálně-chemické vlastnosti olovnatých fosforečnanových skel připravených v kompoziční řadě (40-x)PbO-xGa2O3-60P2O5 (x=0-35). Při záměně PbO za Ga2O3 klesá měrná hmotnost a index lomu skel, zatímco jejích molární objem roste. Odolnost skel vůči působení vody je vysoká. Z dilatometrických křivek vyplynulo, že s rostoucím obsahem Ga2O3 vzrůstá teplota skelné transformace a dilatometrická teplota měknutí skel, zatímco jejich teplotní roztažnost klesá. Studium skel pomocí DSC ukázalo, že přechlazené skelné taveniny při zahřívání krystalizují v teplotním rozmezí  400-800°C za vzniku Pb(PO3)2, Ga(PO3)3 a GaPO4., The effect of Ga2O3 on thermal behaviour and properties of glasses in compositional series (40-x)PbO-xGa2O3-60P2O5 (x=0-35) was investigated. DSC, TD and hot-stage microscopy studies showed that glass transformation temperature, dilatometric softening temperature, crystallization temperature and flow temperature increases with increasing Ga2O3 content, whereas thermal expansion coefficient decreases. Most of glasses crystallize under heating within the range of 400-800°C. Compounds formed by crystallization were Pb(PO3)2, Ga(PO3)3 and GaPO4.

This contribution describes the effect of HMS-Ti substrate decoration with variable amounts of Ga2O3 on the catalytic response of bifunctional Ga2O3/HMS-Ti catalysts in the hydroisomerization of ortho-xylene carried out in a batch reactor at 300 °C. The effect of hydrogen pressure (5, 10 and 40 bar) was investigated. The synthetized Ga2O3/HMS-Ti samples were characterized by variety of techniques: HRTEM, XRD, N2 adsorption–desorption isotherms, FTIR in the –OH region, TPR and XPS. The catalyst activity showed a volcano-type curve being the catalyst with Ga loading of 1.1 wt.% the most active among the catalysts studied. Both FT-IR spectra of adsorbed pyridine and HRTEM images indicated that this behavior is linked to its high Brønsted and Lewis acidities and presence of small Ga2O3 particles homogeneously dispersed on the support surface. All catalysts exhibited larger isomerization than hydrogenation of ortho-xylene. At equilibrium, the products detected were meta- and para-xylenes, and dimethylcyclohexane (DMCH); meta-xylene being the main reaction product. An increase of hydrogen pressure from 5 to 10 bar led to an increase of isomerization and hydrogenation of ortho-xylene. Further increase of the hydrogen pressure from 10 to 40 bar had a very small effect on the catalyst activity.

In this thesis the material systems zinc oxide, aluminum nitride and gallium oxide were investigated by electron paramagnetic resonance and optical spectroscopy in order to gain insight into the point defects in these materials which are affecting the optical and electrical properties. For a long time doping with nitrogen was thought to be the best possibility to create p-type conducting ZnO. However, recently there were doubts whether nitrogen forms a shallow acceptor or not. That acceptor level and the corresponding photo-transition process were characterized by EPR and photo-EPR. The photo-transition process charging the nitrogen acceptor from the negative charged non-paramagnetic state into the neutral paramagnetic, was found to be a direct process to the conduction band with an optical ionization energy Eopt = 2.1 eV. Therefore, it was proven, that the defect caused by a nitrogen atom substituting an oxygen atom in ZnO, forms a deep acceptor level. The characterization of aluminum nitride bulk crystals by EPR reveals two defects, a donor and an acceptor. The donor which originates most likely from an oxygen atom substituting a nitrogen atom has a negative U-behavior and forms a DX- center. The optical ionization energy of the DX- center was determined to 1.9 eV and the formation energy was estimated to 3 meV. A (V_{Al}-O_N) defect complex is most likely the origin of the acceptor observed in the EPR measurements. The presence of (V_{Al}) and (O_N) is confirmed by optical spectroscopy and further the formation of (V_{Al}-O_N) defect complexes is thermodynamically favored over the isolated defects. The energy level position is estimated to be 1.1 eV to 3.5 eV above the valence band. Transition metal ions are often incorporated in semiconductors as residual impurities and form deep level defects. In the case of gallium oxide two 3d transitions metals could be identified by EPR. Co2+ with a 3d7 electron configuration, located at an octahedral gallium lattice site, In dieser Dissertation wurden die Materialsysteme Zinkoxid, Aluminiumnitrid und Galliumoxid mit Elektronenspinresonanz (ESR) und optischer Spektroskopie untersucht um mehr Informationen über Punktdefekte in den Materialien zu erhalten, welche die optischen und elektrischen Eigenschaften stark beeinflussen. Lange Zeit galt Stickstoff als einer der aussichtsreichsten Kandidaten um p-leitendes ZnO herzustellen. Allerdings häuften sich in letzter Zeit Anzeichen dafür, dass Stickstoff keinen flachen Akzeptor in ZnO formt. Um dieses Verhalten zu überprüfen wurden die Energieniveauposition und der dazugehörige Photo-Prozess des Stickstoffzentrums in ZnO mittel ESR und Photo-ESR untersucht. Bei dem Photo-Prozess der das Stickstoffzentrum von seinem negativ geladenen und nicht paramagnetischen Zustand in den neutralen paramagnetischen Zustand umlädt handelt es sich um einen direkten Prozess zum Leitungsband mit einer optischen Ionisierungsenergie von 2,1 eV. Damit konnte endgültig bewiesen werden das es ich bei N_O in ZnO um einen tiefen Akzeptor handelt. Die ESR-Untersuchungen von AlN zeigen einen Donator und einen Akzeptor. Das Donatorsignal ist höchstwahrscheinlich auf ON mit einer negativen Korrelationsenergie zurückzuführen und formt ein DX--Zentrum mit einer optischen Ionisierungsenergie von 1,9 eV. Die Energiebarriere zwischen dem metastabilen O_N und dem DX^--Zentrum beträgt 3 meV. Der Ursprung des ESR-Akzeptorsignals ist höchstwahrscheinlich ein (V-{Al}-O_N) Defektkomplex. Die Existenz von (V_{Al}) und (O_N) ist durch Photolumineszenz- und Absorptions-Messungen bestätigt, außerdem ist die Bildung von (V_{Al}-O_N) Defektkomplexen thermodynamisch erstrebenswerter als das Vorhandensein der isolierten Störstellen. Die Energieniveauposition des Akzeptors befindet sich 1,1 eV bis 3,5 eV über dem Valenzband. Übergangsmetalle sind oft als Restverunreinigungen in Halbleitern vorhanden und bilden tiefe Störstellen. In Galliumoxid konnten mittels ESR zwei 3d-Übergangsmetalle i

beta-Ga2O3 one-dimensional (ID) nanostructures including nanowires, nanoribbons and nanosheets were synthesized via a combined carbon thermal reduction and chemical vapor deposition (CVD) approach. All of these nanostructures consist of single-crystalline monoclinic structure, which has been confirmed via high-resolution TEM and electron diffraction analysis. We obtained beta-Ga2O3 nanowires at high temperature zone, nanosheets, and nanoribbons at medium temperature zone at low-pressure environments. We found that beta-Ga2O3 nanowires and nanoribbons have diversified different growth directions. The optical properties of beta-Ga2O3 nanowires and nanoribbons from UV-vis spectra show that the bandgaps are red-shifted by 0.13 eV.

beta-Ga2O3 one-dimensional (ID) nanostructures including nanowires, nanoribbons and nanosheets were synthesized via a combined carbon thermal reduction and chemical vapor deposition (CVD) approach. All of these nanostructures consist of single-crystalline monoclinic structure, which has been confirmed via high-resolution TEM and electron diffraction analysis. We obtained beta-Ga2O3 nanowires at high temperature zone, nanosheets, and nanoribbons at medium temperature zone at low-pressure environments. We found that beta-Ga2O3 nanowires and nanoribbons have diversified different growth directions. The optical properties of beta-Ga2O3 nanowires and nanoribbons from UV-vis spectra show that the bandgaps are red-shifted by 0.13 eV.

beta-Ga2O3 one-dimensional (ID) nanostructures including nanowires, nanoribbons and nanosheets were synthesized via a combined carbon thermal reduction and chemical vapor deposition (CVD) approach. All of these nanostructures consist of single-crystalline monoclinic structure, which has been confirmed via high-resolution TEM and electron diffraction analysis. We obtained beta-Ga2O3 nanowires at high temperature zone, nanosheets, and nanoribbons at medium temperature zone at low-pressure environments. We found that beta-Ga2O3 nanowires and nanoribbons have diversified different growth directions. The optical properties of beta-Ga2O3 nanowires and nanoribbons from UV-vis spectra show that the bandgaps are red-shifted by 0.13 eV.

beta-Ga2O3 one-dimensional (ID) nanostructures including nanowires, nanoribbons and nanosheets were synthesized via a combined carbon thermal reduction and chemical vapor deposition (CVD) approach. All of these nanostructures consist of single-crystalline monoclinic structure, which has been confirmed via high-resolution TEM and electron diffraction analysis. We obtained beta-Ga2O3 nanowires at high temperature zone, nanosheets, and nanoribbons at medium temperature zone at low-pressure environments. We found that beta-Ga2O3 nanowires and nanoribbons have diversified different growth directions. The optical properties of beta-Ga2O3 nanowires and nanoribbons from UV-vis spectra show that the bandgaps are red-shifted by 0.13 eV.

V diplomové práci je popsán návrh, konstrukce a testování termálního zdroje svazku atomárního kyslíku, který je určen k růstu tenkých oxidových vrstev v podmínkách ultra vysokého vakua. První kapitola pojednává o teorii spjaté s termální disociací a tvorbou atomárních svazků. Dále jsou uvedeny hlavní typy zdrojů svazků atomárního kyslíku a jeho aplikace. Experimentální část je věnována samotnému návrhu zařízení, konstrukci a jeho složení. V poslední část je popsáno testování vlivu atomárního kyslíku na vznik oxidových vrstev (stechiometricky Ga2O3) na nanokapičkách Ga na křemíkovém substrátu připraveného molekulární svazkovou epitaxí. Chemické složení a morfologie připravených nanostruktur jsou zkoumány metodou XPS, SEM a TEM., This diploma thesis describes the design, construction, and testing of a thermal atomic oxygen beam source for the growth of thin oxide layers under ultra-high vacuum conditions. The first chapter discusses the theory associated with thermal dissociation and atomic beam formation. Then, the main types of atomic oxygen beam sources and their applications are presented. The experimental part is devoted to the actual design, construction and assembly of the device. The last part describes the testing of the effect of atomic oxygen on the formation of oxide layers (stoichiometrically Ga2O3) on Ga nanodroplets prepared by molecular beam epitaxy on a Si substrate. The chemical composition and morphology of the prepared nanostructures are studied by XPS, SEM and TEM.

V diplomové práci je popsán návrh, konstrukce a testování termálního zdroje svazku atomárního kyslíku, který je určen k růstu tenkých oxidových vrstev v podmínkách ultra vysokého vakua. První kapitola pojednává o teorii spjaté s termální disociací a tvorbou atomárních svazků. Dále jsou uvedeny hlavní typy zdrojů svazků atomárního kyslíku a jeho aplikace. Experimentální část je věnována samotnému návrhu zařízení, konstrukci a jeho složení. V poslední část je popsáno testování vlivu atomárního kyslíku na vznik oxidových vrstev (stechiometricky Ga2O3) na nanokapičkách Ga na křemíkovém substrátu připraveného molekulární svazkovou epitaxí. Chemické složení a morfologie připravených nanostruktur jsou zkoumány metodou XPS, SEM a TEM., This diploma thesis describes the design, construction, and testing of a thermal atomic oxygen beam source for the growth of thin oxide layers under ultra-high vacuum conditions. The first chapter discusses the theory associated with thermal dissociation and atomic beam formation. Then, the main types of atomic oxygen beam sources and their applications are presented. The experimental part is devoted to the actual design, construction and assembly of the device. The last part describes the testing of the effect of atomic oxygen on the formation of oxide layers (stoichiometrically Ga2O3) on Ga nanodroplets prepared by molecular beam epitaxy on a Si substrate. The chemical composition and morphology of the prepared nanostructures are studied by XPS, SEM and TEM.

V diplomové práci je popsán návrh, konstrukce a testování termálního zdroje svazku atomárního kyslíku, který je určen k růstu tenkých oxidových vrstev v podmínkách ultra vysokého vakua. První kapitola pojednává o teorii spjaté s termální disociací a tvorbou atomárních svazků. Dále jsou uvedeny hlavní typy zdrojů svazků atomárního kyslíku a jeho aplikace. Experimentální část je věnována samotnému návrhu zařízení, konstrukci a jeho složení. V poslední část je popsáno testování vlivu atomárního kyslíku na vznik oxidových vrstev (stechiometricky Ga2O3) na nanokapičkách Ga na křemíkovém substrátu připraveného molekulární svazkovou epitaxí. Chemické složení a morfologie připravených nanostruktur jsou zkoumány metodou XPS, SEM a TEM., This diploma thesis describes the design, construction, and testing of a thermal atomic oxygen beam source for the growth of thin oxide layers under ultra-high vacuum conditions. The first chapter discusses the theory associated with thermal dissociation and atomic beam formation. Then, the main types of atomic oxygen beam sources and their applications are presented. The experimental part is devoted to the actual design, construction and assembly of the device. The last part describes the testing of the effect of atomic oxygen on the formation of oxide layers (stoichiometrically Ga2O3) on Ga nanodroplets prepared by molecular beam epitaxy on a Si substrate. The chemical composition and morphology of the prepared nanostructures are studied by XPS, SEM and TEM.

V diplomové práci je popsán návrh, konstrukce a testování termálního zdroje svazku atomárního kyslíku, který je určen k růstu tenkých oxidových vrstev v podmínkách ultra vysokého vakua. První kapitola pojednává o teorii spjaté s termální disociací a tvorbou atomárních svazků. Dále jsou uvedeny hlavní typy zdrojů svazků atomárního kyslíku a jeho aplikace. Experimentální část je věnována samotnému návrhu zařízení, konstrukci a jeho složení. V poslední část je popsáno testování vlivu atomárního kyslíku na vznik oxidových vrstev (stechiometricky Ga2O3) na nanokapičkách Ga na křemíkovém substrátu připraveného molekulární svazkovou epitaxí. Chemické složení a morfologie připravených nanostruktur jsou zkoumány metodou XPS, SEM a TEM., This diploma thesis describes the design, construction, and testing of a thermal atomic oxygen beam source for the growth of thin oxide layers under ultra-high vacuum conditions. The first chapter discusses the theory associated with thermal dissociation and atomic beam formation. Then, the main types of atomic oxygen beam sources and their applications are presented. The experimental part is devoted to the actual design, construction and assembly of the device. The last part describes the testing of the effect of atomic oxygen on the formation of oxide layers (stoichiometrically Ga2O3) on Ga nanodroplets prepared by molecular beam epitaxy on a Si substrate. The chemical composition and morphology of the prepared nanostructures are studied by XPS, SEM and TEM.

V diplomové práci je popsán návrh, konstrukce a testování termálního zdroje svazku atomárního kyslíku, který je určen k růstu tenkých oxidových vrstev v podmínkách ultra vysokého vakua. První kapitola pojednává o teorii spjaté s termální disociací a tvorbou atomárních svazků. Dále jsou uvedeny hlavní typy zdrojů svazků atomárního kyslíku a jeho aplikace. Experimentální část je věnována samotnému návrhu zařízení, konstrukci a jeho složení. V poslední část je popsáno testování vlivu atomárního kyslíku na vznik oxidových vrstev (stechiometricky Ga2O3) na nanokapičkách Ga na křemíkovém substrátu připraveného molekulární svazkovou epitaxí. Chemické složení a morfologie připravených nanostruktur jsou zkoumány metodou XPS, SEM a TEM., This diploma thesis describes the design, construction, and testing of a thermal atomic oxygen beam source for the growth of thin oxide layers under ultra-high vacuum conditions. The first chapter discusses the theory associated with thermal dissociation and atomic beam formation. Then, the main types of atomic oxygen beam sources and their applications are presented. The experimental part is devoted to the actual design, construction and assembly of the device. The last part describes the testing of the effect of atomic oxygen on the formation of oxide layers (stoichiometrically Ga2O3) on Ga nanodroplets prepared by molecular beam epitaxy on a Si substrate. The chemical composition and morphology of the prepared nanostructures are studied by XPS, SEM and TEM.

V diplomové práci je popsán návrh, konstrukce a testování termálního zdroje svazku atomárního kyslíku, který je určen k růstu tenkých oxidových vrstev v podmínkách ultra vysokého vakua. První kapitola pojednává o teorii spjaté s termální disociací a tvorbou atomárních svazků. Dále jsou uvedeny hlavní typy zdrojů svazků atomárního kyslíku a jeho aplikace. Experimentální část je věnována samotnému návrhu zařízení, konstrukci a jeho složení. V poslední část je popsáno testování vlivu atomárního kyslíku na vznik oxidových vrstev (stechiometricky Ga2O3) na nanokapičkách Ga na křemíkovém substrátu připraveného molekulární svazkovou epitaxí. Chemické složení a morfologie připravených nanostruktur jsou zkoumány metodou XPS, SEM a TEM., This diploma thesis describes the design, construction, and testing of a thermal atomic oxygen beam source for the growth of thin oxide layers under ultra-high vacuum conditions. The first chapter discusses the theory associated with thermal dissociation and atomic beam formation. Then, the main types of atomic oxygen beam sources and their applications are presented. The experimental part is devoted to the actual design, construction and assembly of the device. The last part describes the testing of the effect of atomic oxygen on the formation of oxide layers (stoichiometrically Ga2O3) on Ga nanodroplets prepared by molecular beam epitaxy on a Si substrate. The chemical composition and morphology of the prepared nanostructures are studied by XPS, SEM and TEM.