Controlling optical properties of the near-surface silicon vacancies in nanostructured silicon carbide via surface passivation*

Silicon carbide (SiC) hosts a number of spin-active color centers (deep level defects), such as the negatively charged silicon vacancy, which are important for use in quantum applications. In their role as qubit-candidates in different applications, these defects are inevitably placed in a nanostructured host. This is mostly done for enhancing the signal from the defects. A recent work showed how finite size and surface effects modify not only the frequencies of the quantum emission from the color centers, but also adversely affect a defect’s photo-stability [PRX QUANTUM 3, 020325 (2022)].  Using density functional theory (DFT)-based calculations, we have explored chemical means of mitigating these detrimental effects of surface states in the as-created SiC nanostructures. We show that surface passivation with hydrogen and/or mixed hydrogen and hydroxyl groups can effectively remove surface states from SiC’s bandgap, thereby reducing their hybridization with the defect states of the near-surface defects. This can also effectively reduce/remove the observed blinking and charge-state conversion of these defects from the bright negatively charged to the neutral dark state.