To summarize this entire thesis, MW-assisted spectroscopy has been proposed as a promising approach to investigate the optical properties of VSi and VV spin defects in 4H- and 6H-SiC. The MW-assisted spectroscopy has enabled to separate the spectrally overlapped contribution of different types of defects. From a PL spectrum containing no overlapping spectral contributions of other defects, the local vibrational mode of all measured VSi and VV in 4H- and 6H-SiC has been found along with the phonon energy and DW factor. The interaction of local vibrational modes with point defects has allowed to understand the spin, optical, mechanical, and thermal properties of these defects. In the investigation of V2 in 4H-SiC, a perfect agreement between the experimental data and theoretical calculation have been obtained. The MW-assisted spectra measured at different resonant frequencies associated with the same defect have been found to reveal the same vibrational mode and DW factor. Furthermore, some new ODMR lines to certain defects have been assigned, which have never been reported before. From the investigation of the V2 VSi in 6H-SiC, it has been found that the temperature does not have a clear influence on the DW factor, but high-fluence electron irradiation has been shown to decrease the DW factor. In the polarization investigation, it has been found that in 6H-SiC, V1 possesses no polarization, V2 shows a strong E||c-axis polarization, while V3 exhibits a strong E⊥c-axis polarization. It has also been demonstrated that the temperature and the orientation of the excitation laser have no influence on the photon polarization. In short, this thesis has demonstrated that MW-assisted spectroscopy is a powerful technique to investigate a large number of spin defects in wide-bandgap semiconducting materials.

In dieser Arbeit werden einzelne atomare Defekte in hexagonalem Bornitrid (hBN) charakterisiert und mögliche Anwendungen aufgezeigt, welche die gefundenen herausragenden optischen Eigenschaften ausnutzen. Solche optisch aktiven Punktdefekte in Halbleitern bergen das Versprechen von skalierbaren und stabilen Einzelphotonenquellen, welche für eine Vielzahl von zukünftigen Anwendungen im Bereich der Quanteninformationstechnologie oder für Präzisionsmessungen benötigt werden. Dementsprechend groß ist das Interesse der Wissenschaftsgemeinde, was sich auch in der Anzahl der untersuchten Defektsysteme widerspiegelt. Das Besondere an dem hier vorliegenden System ist zum einen die Zweidimensonalität des Halbleiter-Wirtskristalls und zum anderen die enorme Helligkeit des Emitters, welche sich in bis zu sechs Millionen mit einem Mikroskop detektierten Photonen pro Sekunde niederschlägt. Darüber hinaus motivieren die Stabilität des Emitters bei Raumtemperatur und die schmale spektrale Linienbreite eine tiefgreifende Analyse dieses Neuzugangs zum Emitterzoo. / In this thesis, single atomic defects in hexagonal boron nitride (hBN) are characterized and possible applications are shown, which take advantage of the outstanding optical properties found. Such optically active point defects in semiconductors hold the promise of scalable and stable single-photon sources, which are needed for a variety of future applications in quantum information technology or for precision measurements. The interest of the scientific community is correspondingly high, which is also reflected in the number of defect systems investigated. The special feature of the system presented here is on the one hand the two-dimensionality of the semiconductor host crystal and on the other hand the enormous brightness of the emitter, which is reflected in up to six million photons per second detected with a microscope. In addition, the stability of the emitter at room temperature and the narrow spectral width motivate a profound analysis of this new addition to the emitter zoo.