Spin and photophysics of carbon-antisite vacancy defect in $4H$ silicon carbide: A potential quantum bit

Silicon carbide with engineered point defects is considered as very promising material for the next generation devices, with applications ranging from electronics and photonics to quantum computing. In this context, we investigate the spin physics of the carbon antisite-vacancy pair that in its positive charge state enables a single photon source. We find by hybrid density functional theory and many-body perturbation theory that the neutral defect possesses a high spin ground state in $4H$ silicon carbide and provide spin-resonance signatures for its experimental identification. Our results indicate the possibility for the coherent manipulation of the electron spin by optical excitation of this defect at telecom wavelengths, and suggest the defect as a candidate for an alternative solid state quantum bit.

Figure 1

Schematic diagram of (a) the four possible configurations of carbon antisite-vacancy pair defects in $4H$ SiC and (b) the corresponding electronic structure in the singlet metastable and triplet ground states. The filled red and the outlined arrows indicate occupied and unoccupied single-particle states, respectively.

Figure 2

Isovalue surface of the spin density and the direction of the spin quantization (green arrows) in the (a) ground-state configuration and (b) metastable configuration of the neutral carbon anti-site vacancy pair at $hh$ lattice configuration. In both cases, the isosurface value of 0.04 was chosen.

Figure 3

The calculated HSE06 formation energies $\left(\Delta H_{\text{form}}\right)$ of the carbon antisite-vacancy pair (CAV), the Si-vacancy $({\mathrm{V}}_{\text{Si}})$, and the C-vacancy $({\mathrm{V}}_{\text{C}})$ defects in $4H$-SiC as a function of the Fermi-level $\left(E_{\text{Fermi}}\right)$ with respect to the valence band maximum $\left(E_{\text{V}}\right)$ in carbon-rich limit. For every defect, the symmetrically inequivalent configurations are depicted separately. The data related to ${\mathrm{V}}_{\text{C}}$ were taken from Refs. [38, 39].

Figure 4

(a) PES of lowest singlet and triplet of the $hh$ complex as obtained within $G_0{W}_0$ and DFT-HSE06 using the 288 atom cell. $Q$ connects the singlet $\left(Q_0^{S=0}\right)$ and the triplet $\left(Q_0^{S=1}\right)$ ground-state (GS) configurations. (b) Absorption spectrum in the configuration of the excited triplet state (ES) as obtained from BSE calculations. Excitation occurs from the triplet GS configuration. The bound excitons are indicated along side with the ionization threshold. The first peak in this spectrum corresponds to the vertical emission energy. The polarization of the photons is indicated where $c$ is the $c$-axis of $4H$ SiC parallel to the symmetry axis of the defect. We note that the bound exciton peak may be sharper; we used a broadening of $\sim 0.05$ eV to produce a continuous absorption spectrum. (c) PES of the triplet states as obtained from BSE calculations (red and green lines). $Q_{\text{exc}}$ connects the triplet GS and ES configurations $(Q_0^{S=1}$ and $Q_{\text{exc}}^{S=1})$. The green line refers to the ${}^3{\text{A}}_1$ state. The ${}^1{\text{A}}_1$ singlet state (solid black line) was obtained from CDFT.