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This work has employed the Micro-wave Plasma enhanced Chemical Vapor Deposition (MPCVD) method to fabricate diamond PN junction device. The n+ <111> orientation single-crystal silicon has used as substrates. P-type diamond layer is doped with B(OCH3)3 and the N-type diamond layer is doped with ammonia. The surface structure of diamond film has been observed by scanning electron microscope; and the device rectification property of a PN junction has measured by current-voltage characteristic. The carrier density and mobility of diamond films have been analyzed by Hall measurement. Furthermore, the Cathodoluminescence (CL) spectroscopy showed the defect spectra in diamond PN junction. The N-type diamond film and P-type diamond film have deposited at temperature of 800 ¢J, for 30 minutes and 90 minutes, respectively. The process CVD has performed in the same chamber continually. A I-V curve of sample showed the set on positive voltage 0.5 V and the reverse breakdown voltage of 6 V. Further, CL results revealed a peak at 285 nm (4.4 eV), which represents the CVD diamond band and the other one is at 500 nm (2.5 eV), which stands for donor-acceptor recombination from defect in these diamond films.

In this thesis I will evaluate few discrete devices and their differences in structure, static and switching characteristics and also some structurall and manufacturing principles. After that I will follow up with their integration into power modules , where I will also aim on construction solutions and trends. These power moduls are today delivered as „stack“ or „system“, where for optimization and highest achievable efficiency of the whole unit the integration of protection, drive and cooloing stage is incorporated. Cooling and drive of some devices will be subject of a separate chapter. Also some of novel materials, which are very promissing, will be introduced. They show improvemnet in electrical and thermal properties. They have potential to replace the currently dominant Silicon in the near future.

<p> In the current research, use of p-n junction GaAs nanowires (NWs) grown by gas source molecular beam epitaxy on GaAs (111) B substrates for the fabrication of flexible solar cells are reported. The solar cells were fabricated by embedding the NWs in a polymer matrix (SU8 2), followed by ohmic contact formation to the tops of the NWs as well as the rear side of the substrate. I-V characteristic curves were obtained by illuminating the solar cells using a solar simulator, indicating a photovoltaic effect. NWs were also detached from the substrate by different methods and successfully transferred onto a flexible substrate for potential use as solar cells. Scanning electron microscopy was used throughout the research for characterization and optimization of the fabrication processes including NW embedment, removal from the substrate, and contact formation.</p> / Thesis / Master of Applied Science (MASc)

Les détecteurs de radiations nucléaires sont des outils importants dans de nombreux domaines tels que dans les réacteurs nucléaires, la sécurité nationale, mais ils sont également primordiaux dans des applications médicales. Les progrès récents dans la technologie des semi-conducteurs permettent la réalisation de détecteurs très efficaces et quasi-insonores qui permettent la détection de différents types de radiations nucléaires. Le carbure de silicium (SiC) est une bande semi-conductrice large, grâce à sa conductivité thermique élevée et à une résistance élevée aux rayonnements, il est adapté pour les environnements difficiles où peuvent exister des flux élevés de température et de rayonnement. Le but du projet européen (I_SMART) est ainsi de prouver la fiabilité de nouvelles méthodes de réalisation de détecteurs de radiations nucléaires et d'étudier leur performance dans différents types d'irradiation (neutrons rapides et thermiques) et à différentes températures. Différentes méthodes ont été utilisées pour réaliser les détecteurs de rayonnement SiC. Par exemple l'implantation d'ions de bore a été utilisé pour créer la couche de conversion de neutrons soit dans le contact métallique ou directement en SiC. Les détecteurs fabriqués ont été testés dans le réacteur nucléaire BR1, mettant en lumière la présence de neutrons thermiques. En outre, ces détecteurs détectent des neutrons rapides sous n’importe quelle température. En outre, les détecteurs utilisés montrent leur stabilité sous différents flux de neutrons qui indiquent la fiabilité de ces nouveaux modes de réalisation de détecteurs de rayonnement qui pourraient remplacer ceux utilisés actuellement. / Nuclear radiation detectors are important tools in many fields such as in nuclear reactors, homeland security and medical applications. Recent advances in semiconductor technology allow construction of highly efficient low noise detectors for different nuclear radiations. Silicon carbide (SiC) is a wide band gap semiconductor with a high thermal conductivity and high radiation resistance. It is suitable for a harsh environment where high temperatures and radiation fluxes may exist. In the framework of the European project (I_SMART) the purpose of this work is to demonstrate the reliability of new methods of realizing nuclear radiation detectors and to study their performance under different types of irradiation (fast and thermal neutrons) and at elevated temperatures. Different methods have been used to realize SiC based-radiation detectors. For instance boron ion implantation has been used to create the neutron converter layer either in the metallic contact or directly in the SiC. The fabricated detectors have been tested in the BR1 nuclear reactor revealing the thermal neutron detection and the feasibility of gamma discrimination from thermal neutrons using one single detector. Such detectors are sensitive to fast neutrons with a stable response under elevated temperatures (up to 150 °C). Furthermore, the studied detectors show stability under different neutron fluxes, indicating a reliability of such new methods of realizing radiation detectors which could replace those of the current state of the art.

The microplasma discharges in the PN junction local defect micro-regions are as a rule, accompanied by the emission of light. This radiation from solar cell PN junctions was measured by means of a optical fibre connected to the optical input of a photomultiplier. By inching the fibre by means of computercontrolled X-Y plotter above the cell surface a 2-D image of the irradiation local regions has been created. It is seen that a cell of a superficial area of 100 square cm contains a large number of defects, which depends on applied reverse voltage. This method can be a convenient tool for study and diagnostics of optoelectronic devices.

In this doctoral thesis the two dimensional material graphene has been studied in depth with particular respect to Zener tunnelling devices. From the hexagonal structure the Hamiltonian at a Dirac point was derived with the option of including an energy gap. This Hamiltonian was then used to obtain the tunnelling properties of various graphene nano-devices; the devices studied include Zener tunnelling potential barriers such as single and double graphene potential steps. A form of the Landauer formalism was obtained for graphene devices. Combined with the scattering properties of potential barriers the current and conductance was found for a wide range of graphene nano-devices. These results were then compared to recently obtained experimental results for graphene nano-ribbons, showing many similarities between nano-ribbons and infinite sheet graphene. The methods studied were then applied to materials which have been shown to possess three dimensional Dirac cones known as topological insulators. In the case of Cd3As2 the Dirac cone is asymmetrical with respect to the z-direction, the effect of this asymmetry has been discussed with comparison to the symmetrical case.

L'absence d'oxydes semi-conducteurs de type p de haute performance retarde le développement de d’électronique transparente et du photovoltaïque à base d’oxydes. Dans le groupe des composés semi-conducteurs, les oxydes à base de cuivre présentent des caractéristiques électriques, optiques et de fabrication prometteuses qui établissent cette famille de matériaux comme bien adaptés aux applications semi-conductrices de type p. Dans ce travail, nous nous concentrons sur la croissance de films minces d’une part de Cu2O dopée par des cations et d’autre part de CuCrO2, visant à améliorer leurs propriétés optiques et électriques. De plus, nous avons mis en œuvre ces films d'oxyde dans des dispositifs de jonction pn tels que des cellules solaires et des photodétecteurs UV.Dans le travail sur Cu2O, nous avons réalisé l'incorporation de magnésium jusqu'à 17% dans des films minces par dépôt chimique en phase vapeur assisté par aérosol, entraînant des changements de morphologie. La résistivité électrique a été réduite jusqu’à des valeurs de 6,6 ohm.cm, en raison de l'augmentation de la densité de porteur de-charges jusqu'à 10^18 cm-3. L'incorporation du magnésium a en outre eu un impact sur la stabilité de la phase Cu2O. En effet la transformation du Cu2O en CuO en conditions oxydantes est considérablement retardée par la présence de Mg dans les films, en raison de l'inhibition de la formation d’un type particulier de lacune de cuivre (split vacancy). L'intégration dans les jonctions pn a été réalisée avec succès en utilisant uniquement des voies de dépôt chimique en phase vapeur, en combinaison avec le ZnO de type n. Néanmoins, l'application de Cu2O dopé au Mg dans les cellules solaires présente un effet photovoltaïc très faible, loin des meilleures valeurs de l’état de l’art.Dans le travail sur CuCrO2, nous démontrons la première fabrication d'hétérostructures de nanofils en configuration cœur/coquille ZnO/CuCrO2 utilisant des techniques de dépôt chimique adaptées pour des grandes surface, à faible coût, facilement implémentées à des températures modérées et leur intégration dans des photodétecteurs UV auto-alimentés. Une coquille conforme de CuCrO2 avec la phase de delafossite et avec une uniformité élevée a été élaborée par un dépôt chimique en phase vapeur assisté par aérosol sur un réseau de nanofils ZnO alignés verticalement, obtenu par dépôt par bain chimique. Les hétérostructures ZnO/CuCrO2 coeur-coquille présentent un comportement rectificatif significatif, avec un ratio de rectification maximal de 5500 à ± 1V, ce qui est bien meilleur que les dispositifs 2D similaires rapportés dans la littérature, ainsi qu'une absorption élevée supérieure à 85% dans la région UV. Lorsqu'ils sont appliqués en tant que photodétecteurs UV auto-alimentés, les hétérojonctions optimisées présentent une réponse maximale de 187 μA / W sous une polarisation nulle à 374 nm ainsi qu'une sélectivité élevée avec un ratio de rejet entre l’UV-et le visible (374-550 nm) de 68 sous irradiance de 100 mW/cm2. / The lack of a successful p-type semiconductor oxides delays the future implementation of transparent electronics and oxide-based photovoltaic devices. In the group semiconducting compounds, copper-based oxides present promising electrical, optical and manufacturing features that establish this family of materials suitable for p-type semiconductor applications. In this work, we focused on the growth of cation doped Cu2O and intrinsic CuCrO2 thin films, aiming for enhancements of their optical and electrical response. Furthermore, we implemented these oxide films into pn junction devices, such as solar cells and UV photodetectors.In the work on Cu2O, we achieved the incorporation of magnesium up to 17% in thin films by aerosol-assisted chemical vapor deposition, resulting in morphology changes. Electrical resistivity was reduced down to values as low as 6.6 ohm.cm, due to the increase of charge-carrier density up to 10^18 cm-3. The incorporation of magnesium had additionally an impact on the stability of the Cu2O phase. The transformation of Cu2O into CuO under oxidizing conditions is significantly postponed by the presence of Mg in the films, due to the inhibition of copper split vacancies formation. The integration into pn junctions was successfully achieved using only chemical vapor deposition routes, in combination with n-type ZnO. Nevertheless, the application of Mg-doped Cu2O in solar cells present a meager photovoltaic performance, far from the state-of-the-art reports.In the work on CuCrO2, we demonstrate the first fabrication of ZnO/CuCrO2 core-shell nanowire heterostructures using low-cost, surface scalable, easily implemented chemical deposition techniques at moderate temperatures, and their integration into self-powered UV photodetectors. A conformal CuCrO2 shell with the delafossite phase and with high uniformity is formed by aerosol-assisted chemical vapor deposition over an array of vertically aligned ZnO nanowires grown by chemical bath deposition. The ZnO/CuCrO2 core-shell nanowire heterostructures present a significant rectifying behavior, with a maximum rectification ratio of 5500 at ±1V, which is much better than similar 2D devices, as well as a high absorption above 85% in the UV region. When applied as self-powered UV photodetectors, the optimized heterojunctions exhibit a maximum responsivity of 187 µA/W under zero bias at 374 nm as well as a high selectivity with a UV-to-visible (374-550 nm) rejection ratio of 68 under an irradiance of 100 mW/cm2.

The thesis deals with the design of the measurement installation, which is intended for the microplasma noise measurements. This noise is being generated in the defective parts of the PN junction. The goal of this work is to design the measurement installation and to realize the fully functional workbench for the analogical noise related measurements and to determine the transfer function of the measurement installation. Main part of the work is to choose proper parameters for the measuring devices and to design the software intended for the automated measurements. Consequently, we have to process the measured waveforms of the microplasma noise, to determine the dependency of the noise on the signal magnitude and to calculate the power spectral noise density. Finally, we have to determine the transfer function of the measurement installation and to design the inversion filter.

This thesis deals with the issue of quantum efficiency measurement of optoelectronic devices. The physical nature of silicon solar cells is explained here. In addition, the quantum efficiency as a concept is introduced. There is also discussed the influence of a solar cell semiconductor structure on the quantum efficiency itself. Furthermore, the thesis is focused on the design of an experimental set-up for automated measurement and data acquisition. The final realization of the step motor control unit is described in detail. It includes local and/or remote operations, design and development motivation. The next chapter is dedicated to analysis of the Matlab source code for remote operation, data acquisition and presentation. The final part of the thesis gives attention to experiments with real structures, not only the solar cells. The obtained results of analyzed measurements are presented at the conclusion.