Enhancing NV concentration in delta-doped diamond via low-pressure high-temperature annealing

We present the increase in the nitrogen vacancy center concentration in nitrogen delta-doped layers by almost one order of magnitude. To achieve this, we employ a low-pressure, high-temperature annealing step at 1750 °C in vacuum. We demonstrate an enhancement of the photoluminescence intensity of NV centers compared to annealing steps at lower temperatures of 1200 °C. To achieve this, we fabricate nitrogen-doped thin films with a thickness of 50 nm via chemical vapor deposition. We show that the nitrogen is mainly incorporated in a 6 nm thin film at the layer interface. We link the strong enhancement of the NV concentration to a possible decomposition of NVH centers and the mobility of various species at elevated temperatures, including vacancies and nitrogen in these two-dimensional structures. Additionally, after the high temperature annealing, we observe a Hahn-echo spin coherence time of 7.9 µs, which is in line with literature data on achievable coherence time in highly nitrogen-doped layers. Our results could pave the way for the precise fabrication of improved diamond elements, e.g., used in magnetic field sensors and offer an alternative route to implantation techniques.