Quantum-Grade Diamond for Cavity-based Solutions

Quantum technologies represent one of the latest achievements of humankind. In this context, synthetic diamond is extensively studied over the past years due to its outstanding material properties. Especially nitrogen-vacancy (NV) centers in diamond show high potential towards the realization of diamond-based quantum technologies. Therefore, this dissertation focuses on the understanding of the fabrication of highly NV-doped bulk diamond defined as quantum grade. This type of diamond is expected to find application as a laser crystal to promote the realization of solid-state masers, laser systems, high sensitivity gyroscopes, high sensitivity magnetometers or more specifically a laser threshold magnetometer. For the implementation of such systems however, special material properties are demanded. These required characteristics were compiled in detail in the course of this thesis and suitable specifications for their evaluation were elaborated. Furthermore, the entire diamond development chain was considered to prevent any inherited detriment. For a successful epitaxy, optimal diamond substrates were selected firstly. These were pretreated with an in situ plasma-etching step to remove their polishing-induced subsurface damage. In this regard, a new non-destructive measurement method was introduced to the diamond community to reliably determine the removal of the damaged layer down to the bulk crystal quality. Additionally, the disadvantage of oxygen as a process-gas component was identified during the optimization of this pretreatment, contrary to the common opinion stated in literature. Subsequently, in situ nitrogen doping of diamond was thoroughly investigated. In this context, the highest ever-reported in situ incorporation efficiencies of NV centers into diamond were obtained. Based on the corresponding findings, a phenomenological model was established on the incorporation mechanism of NV centers into diamond. Moreover, the scientific and technical understanding of the incorporation of single substituted nitrogen into diamond and its influences as a catalyst were advanced. In this relation, the impact of diverse direct input variables over a wide range on the plasma properties was identified and correlated with the resulting defect states within the synthesized diamond. This elaborated data illustrates the high potential of engineering defect concentrations as well as crystal quality of the desired growth product. Based on these essential dependencies, optimal growth regimes were determined towards the realization of the desired quantum-grade diamond. In conclusion, it can be stated that the optimized diamonds, synthesized in the course of this thesis, meet the high demands of the as-grown preliminary quantum-grade diamond. Subsequent adequate posttreatments enable these diamonds to be suitable for further development in the context of cavity-based diamond quantum technological applications.