Positively charged carbon vacancy defect as a near-infrared emitter in 4H-SiC

Certain intrinsic point defects in silicon carbide are promising quantum systems with efficient spin-photon interface. Despite carbon vacancy in silicon carbide being an elementary and relatively abundant intrinsic defect, no optical signal has been reported associated with it. Here, we revisit the positively charged carbon vacancy defects in the 4H polytype of silicon carbide (4H-SiC) by means of ab initio calculations. We unveil the origin of thermal averaging observed in the EI5 electron spin resonance center associated with the so-called k-site configuration of carbon vacancy as phonon excitations in the strongly coupled electron-phonon system. We further find that the excited state is optically active for the so-called h-site configuration of carbon vacancy, with zero-phonon line at $0.65\mathrm{eV}$. This defect shows a strong emission with a 9.3 ns optical lifetime. Moreover, the deteriorating effects of phonons on its optical properties are relatively weak, evinced by the calculated quantum efficiency and Debye-Waller factor of 27% and 20%, respectively. Based on these findings, we propose this defect as an exotic paramagnetic near-infrared emitter in the IR-B region.

Figure 1

Electronic level diagrams of the ${\text{V}}_{\mathrm{C}}^{+}$ defect in ${\text{C}}_{3\text{v}}$ symmetry at (a) h site and (b) k site and (c) in ${\text{C}}_{1\text{h}}$ symmetry at k site. Each Kohn-Sham level is labeled according to the irreducible representations of the corresponding point group symmetry. The conduction band (CB) and the valence band (VB) are shown in green and blue colors, respectively.

Figure 2

Spin density of the ${\mathrm{V}}_{\text{C}}^{+}$ defect at (a) h site with ${\text{C}}_{3\text{v}}$ symmetry and (b) k site with ${\text{C}}_{1\text{h}}$ symmetry. The spin density is defined as the charge density difference between the majority and minority spin channels in the spin-polarized calculation. The plotted isosurface corresponds to a positive spin density. The hyperfine parameters for the atoms labeled here are given in Table 1.

Figure 3

Adiabatic potential energy surfaces in the function of configuration coordinates corresponding to (a) $E$- and (b) $T$-symmetric distortions in the ${\mathrm{V}}_{\text{C}}^{+}$ defect at k site. The fitted curve corresponds to the linear Jahn-Teller solution of the $T\times (e+t_{\text{2}})$ problem.

Figure 4

Simulated PL spectrum of the h-site ${\text{V}}_{\text{C}}^{+}$ defect. The calculated HR and DW factors are 1.605 and $20\%$, respectively.

Figure 5

Calculated nonradiative lifetime of the h-site ${\text{V}}_{\text{C}}^{+}$ defect in the function of temperature.