Chemical vapour deposition diamond single crystals with nitrogen-vacancy centres: a review of material synthesis and technology for quantum sensing applications

Abstract

Diamond is a host for a wide variety of colour centres that have demonstrated outstanding physical and optical properties. Among them the nitrogen-vacancy (NV) centre is the most investigated. These defects can be created on demand and optically manipulated allowing foreseeing the development of highly sophisticated quantum devices in particular for sensing magnetic fields. Nevertheless harnessing the potential of these centres mainly relies on the availability of high quality and purity diamond single crystals that need to be specially designed and engineered. Microwave plasma assisted chemical vapour deposition has become a key enabling technology in this field of research. Nitrogen can indeed be directly in-situ doped into a high crystalline quality diamond matrix in a controlled way. Single isolated centres or ensembles can then be investigated or integrated into a device without the need of any additional post-treatment. In this paper we will provide an overview on the requirements for synthesizing quantum grade diamond material by CVD. By limiting defects, impurities and surrounding spins, long coherence times have been achieved. A high NV creation yield and a controlled density over a wide range of concentration, from a few ppb to a few ppm is also a pre-requisite to many applications. Efforts have been dedicated to controlling the spatial localization of colour centres both in-depth and in-plane (creation of arrays) while ensuring a stable charge state and good photostability. Finally, the ability to promote specific crystalline orientations among the 4 possible axes of the NVs has been demonstrated by growing on specific substrate orientations such as (110), (111) and (113). These achievements and progresses made over the past decade on the material synthesis aspects, have contributed to position diamond as one of the most promising solid-state quantum system and the first industrial applications are just starting to emerge in this field.