Ab initio study of substitutional nitrogen in silicon: linking the defect to its spectroscopic properties

Nitrogen impurities in silicon have proven to enhance its mechanical and chemical properties. They are also foreseen as promising candidates for qubits as they might enable room-temperature operations and are already compatible with existing industrial production lines. However, nitrogen is highly reactive in silicon. It recombines with vacancies and other impurities, thus resulting in the formation of a wide variety of defects and defect-complexes that can exist in different charge states. Such a diversity of defects leads to ambiguous experimental identification. Indeed, for the simple case of substitutional nitrogen, there is still an ongoing debate on its fundamental properties, such as the number and nature (shallow or deep) of its charge transition levels (CTL). In this work, we focus on the substitutional nitrogen impurity (N_Si) and propose a theoretical model that bridges the atomic scale structure and its corresponding spectroscopic signature. We perform ab initio calculations to sample the potential energy surface of the N_Si system. The resulting defect configurations are grounded in group theory considerations and linked to the pseudo Jahn-Teller effect. Moreover, we compute EPR parameters and CTL of N_Si which allows for direct comparison with experiments (EPR/DLTS).