Investigation of nitrogen-vacancy centre creation in thin single-crystal diamond films grown with a Distributed Antenna Array microwave reactor

In this work, a Distributed Antenna Array (DAA) microwave system, comprising 16 plasma sources arranged in a 2D matrix, is successfully used for the deposition of nitrogen-doped single-crystal diamond (SCD) layers of few hundreds of nanometers in thickness using H2/CH4/O2/N2 gas mixtures. Operating at low pressure (< 1 mbar), this system provides low growth rates (< 120 nm.h⁻¹), ensuring precise control over layer thickness and NV positioning. The purpose is to refine both growth and post-treatment processes in order to improve nitrogen-vacancy (NV) centre creation in terms of precise positioning and spin properties for applications in quantum technology. He+ implantation at 9 keV and varying doses between 1012 to 5x1013 ions.cm-2 are used on the nitrogen doped layers to ensure vacancies creation, followed by an annealing step at 800 °C to promote the formation of NV centers. A nitrogen concentration of 1000 ppm in the feed gas combined with an implantation dose of 1.6x1012 ions.cm-2 appears to be the optimal compromise between nitrogen incorporation and NV density. Under these conditions, the NV ensemble exhibits a spin dephasing time T2* of 91 ns while maintaining a strong photoluminescence signal.