Optimization of NV^-/N_s Ratio of CVD Single Crystal Diamond for Quantum Applications

The development of applications in quantum sensing requires dedicated solid-state material platforms with unprecedented control over quality, purity and doping. Indeed, Quantum Technologies (QT) explore our ability to coherently control the peculiar properties of nanoscale quantum systems and harness their potential in a wide range of fields including health, communications, security and environment. The negatively charged nitrogen-vacancy centre (so-called NV^- centre) in diamond is one of the most promising systems for such applications because of the possibility to optically manipulate and read out the spin state of this defect, even at room temperature. These specific spin properties have paved the way to ultra-sensitive, high-performance and innovative quantum sensors (magnetometers, gyroscopes, spectrum analysers, etc.) which could open up perspectives in investigating properties that would remain inaccessible by conventional devices. For the development of these applications, it is necessary to have diamond films of very high crystalline quality in which the density, environment, orientation and spatial localization of the introduced colour centres are perfectly controlled. Microwave Plasma-Assisted Chemical Vapour Deposition (PACVD) as a diamond growth method, offers very good prospects in engineering such a material [1]. Nevertheless, obtaining high densities of NV centres (&gt; 500 ppb) with good coherent properties remains particularly difficult due to the low conversion efficiency between substitutional nitrogen N_S and NV centres.<br/>In this presentation, we will present the optimization of the CVD growth conditions and associated post-treatments to maximize the NV^-/Ns ratio in bulk material for a constant nitrogen precursor concentration in the gas phase. In a first part, we will focus more particularly on growth on a (100) orientation coupled with a post electronic irradiation allowing reaching a yield close to 20 %. In a second part, we will show that the use of alternative orientations with N₂O as a dopant gas and appropriate growth conditions, allows not only to reach quasi-preferential orientation of the NV centers but also a NV/Ns ratio above 20% even without any specific post-treatments. This is an extremely high value for a non-irradiated, i.e. as-grown, diamond film and an important step towards the production of specially engineered a quantum grade diamond material.<br/>[1] J. Achard. V. Jacques. A. Tallaire. Chemical vapour deposition diamond single crystals with nitrogen-vacancy centres: a review of material synthesis and technology for quantum sensing applications. Journal of Physics D: Applied Physics. 53 (2020) 313001. http://dx.doi.org/10.1088/1361-6463/ab81d1