A carbon-nitrogen complex in Si for spin qubits and single-photon emitters

We propose a carbon-nitrogen (CN) impurity complex in silicon for applications in quantum information science, including as a spin qubit or single-photon emitter. This complex is isoelectronic to the T center, which has been actively pursued for such applications, yet its stability is sensitive to the hydrogen content in the environment. Using density functional theory and hybrid functionals, we show that the CN complex is stable against decomposition to simpler defects, and has a similar electronic structure and optical properties (including zero-phonon line and radiative lifetime) to the T center. To predict the optical properties, due to the presence of a bound exciton, we carefully choose the functional and handle the supercell-size scaling, and propose a new method to incorporate the hydrogenic nature of the exciton. Given its similarity to the T center while avoiding problems associated with hydrogen, we believe that the CN complex is a promising alternative.