First principles insights into the conversion between A-type and B-type G centers in silicon

The design and synthesis of solid-state point defects in silicon is a prominent strategy for integrating quantum-enabled technology with existing semiconductor electronics. Of the known defects in silicon, the G center, composed of two carbon atoms and an interstitial silicon atom, is an attractive candidate due to its telecom O-band optical emission and an intersystem crossing to a spin triplet state. Populations of G centers in silicon exist as ensembles of dark A-type (GCA) and optically bright B-type (GCB) configurations. Understanding the interconversion between GCA and GCB can inform protocols to control the distribution of G center populations, i.e., to toggle between dark and bright quantum point defects. Our ab initio calculations show that ionization of the G center slightly shifts the defect formation energies such that GCB is more stable at a neutral charge state, while GCA is more stable at -1 and +1 charge states. Incorporation of a hydrogen atom (H) with the defect structures was found to exaggerate formation energy differences, indicating that H acts to destabilize GCB defects. Nudged elastic band (NEB) calculations revealed the relative energy barriers separating GCA and GCB configurations both with and without an interacting H atom, which confirmed that relevant transition states between GCA and GCB are also sensitive to the charge state and hydrogenation. Our work informs strategies for the programmable synthesis of bright G centers in silicon.