First-principles insights into the atomic structure of carbon-nitrogen-oxygen complex color centers in silicon

Abstract

Spin-active color centers are the basis of solid-state defect systems utilized in quantum technologies. Although silicon is an emerging host material for quantum defects, there is an urgent need to characterize color centers with non-zero electron spin ground state in this platform, beside the prominent T-center. In this work, we carry out first-principles calculations to identify the possible atomic structures originating the experimentally observed N-line series in silicon. We propose that the core structure of the N1 center consists of a neighboring carbon and nitrogen interstitial atoms. Furthermore, we predict that more complex defects involving self-interstitial and interstitial oxygen atoms are feasible candidates for the further lines in the series. As all of these color centers are isoelectronic structures to the T-center, they provide a family of alternative spin doublet qubits with emission near the low-energy telecommunication bands.

Figures (7)

• Figure 1: Binding and formation energy plots of carbon and nitrogen interactions in silicon as a function of the interatomic distance. The lines connecting the calculation points in equilibrium geometries are interpolations to guide the eye along the pair formation path. For the three-center interstitial defects of C-N-Si (red), only the lowest energy configurations are shown for each defect motif (see Sec. \ref{['sec:motif']}). The corresponding structures of the latter are visualized in Fig. \ref{['fig:motif']}
• Figure 2: Structural motifs of the lowest energy tri-interstitial silicon aggregates (upper row) serving as templates for the $\text{C}_\text{i}\text{N}_\text{i}\text{Si}_\text{i}$ complex defect search. The resulting lowest energy configurations are shown under each parent motif. Si, N, and C atoms are drawn in dark blue, light blue, and brown, respectively.
• Figure 3: Binding energy plot of oxygen interactions with the core structures of selected N1 and N2 candidate defects in silicon as a function of the C-O distance. The lines connecting the calculation points in equilibrium geometries are interpolations to guide the eye along the pair-formation path.
• Figure 4: Calculated formation energy diagram in the silicon bandgap for the candidate defects with the largest binding energies. The search for candidates with a single stable transition level compatible with pseudo-acceptor bound exciton centers rules out $\text{C}_\text{i}\text{N}_\text{i}\text{Si}_\text{i}$ (hexa) and (split) configurations.
• Figure 5: Comparison of the calculated phonon sideband (blue) of the $\text{C}_\text{i}\text{N}_\text{i}$ defect to the experimental sideband of the N1 emitter reported in Ref. Dornen_1985 (red). Two localized vibration modes are identified in the calculated spectrum at 66.8 meV and 118.9 meV. The calculated total Huang-Rhys factor of 1.06 corresponds to a Debye-Waller factor of 0.35.