Optical absorption spectra of the T-Center defect in Silicon computed via the BSE@GW@PBE approach

The T-Center defect in silicon is composed of a substitutional carbon atom, an interstitial carbon atom, and an interstitial hydrogen atom, in the standard diamond-lattice silicon structure. Its optical emission in the telecom O band and its composition of silicon and Earth-abundant elements make the T-Center a compelling defect structure to assist with, for example, spin-photon coupling of quantum information. Despite its significant potential in photonic devices, the electronic structure of the T-Center's defect levels pose challenges. Namely, the relevant optically excited electron-hole pair has the hole located within the bulk valence band while the electron is excited to a localized in-gap defect state. In this work, we discuss the optical spectrum of the T-Center computed via the GW-BSE approach from many-body perturbation theory, using a density functional theory starting-point calculation employing standard PBE exchange-correlation functionals. These results, computed with supercells of increasing size to allow for improved treatment of the electron-hole excitation, are compared with optical absorption spectra computed with density functional theory employing hybrid functionals.