Theoretical study of quantum emitters in two-dimensional silicon carbide monolayers

The electronic and optical features of some potential single-photon sources in two-dimensional silicon carbide monolayers is studied via ab initio calculations and group theory analyses. A few point defects in three charge states (negative, positive, and neutral) are considered. By applying performance criteria, Stone-Wales defects without and with combination of antisite defects are studied in detail. The formation energy calculations reveal that neutral and positive charge states of these defects are stable. We compute the zero-phonon-line energy, the Huang-Rhys (HR) factor, and the photoluminescence spectrum for the available transitions in different charge states. The calculated HR values and the related Debye-Waller factors guarantee that the Stone-Wales defects have a high potential of performing as a promising single-photon emitter.

Figure 1

Atomic structure of (a) SW, (b) $\mathrm{S}\mathrm{W}-{\mathrm{Si}}_{\text{C}}$, and (C) $\mathrm{S}\mathrm{W}-{\mathrm{C}}_{\text{Si}}$ defects. Silicon and carbon atoms are illustrated by blue and black colors, respectively

Figure 2

The electronic structure (to the scale) of the three SW defects thoroughly studied in this work in the neutral and positive charge states. The solid arrows indicate allowed dipole transitions. The transitions with in-plane polarization are expected to give brighter emissions (red) while the transitions induced by the out-of-plane dipole moments are presented in orange (weaker excitation). Dashed and dotted blue arrows show the nonradiative transitions that can be induced by spin interactions.

Figure 3

Formation energy as a function of the Fermi level for SW (red lines), $\mathrm{S}\mathrm{W}-{\mathrm{Si}}_{\text{C}}$ (green lines), and $\mathrm{S}\mathrm{W}-{\mathrm{C}}_{\text{Si}}$ (blue lines) defects in C-rich (solid lines) and Si-rich (dashed lines) growth conditions. Both growth conditions for SW defect are the same.

Figure 4

Kohn-Sham ground state electronic levels of (a) SW, (c) $\mathrm{S}\mathrm{W}-{\mathrm{Si}}_{\text{C}}$, and (e) $\mathrm{S}\mathrm{W}-{\mathrm{C}}_{\text{Si}}$ defects. Occupied and unoccupied levels are shown with solid black lines and blue dashed lines. Charge density plots for neutral defect states are displayed in (b) SW, (d) $\mathrm{S}\mathrm{W}-{\mathrm{Si}}_{\text{C}}$, and (f) $\mathrm{S}\mathrm{W}-{\mathrm{C}}_{\text{Si}}$. The symmetry of molecular orbitals are shown both next to the energy levels and the charge density plots. The $C_{2v}$ symmetry labels are also used for the SW defect.

Figure 5

Photoluminescence line shape of the first excitation of neutral Stone-Wales defects.