Electrically and Mechanically Tunable Electron Spins in Silicon Carbide Color Centers

The electron spins of semiconductor defects can have complex interactions with their host, particularly in polar materials like SiC where electrical and mechanical variables are intertwined. By combining pulsed spin resonance with ab initio simulations, we show that spin-spin interactions in $4H\text{−}\mathrm{SiC}$ neutral divacancies give rise to spin states with a strong Stark effect, sub-${10}^{-6}$ strain sensitivity, and highly spin-dependent photoluminescence with intensity contrasts of 15%–36%. These results establish SiC color centers as compelling systems for sensing nanoscale electric and strain fields.

Figure 1

(a) A $4H\text{−}\mathrm{SiC}$ membrane is epoxied to the top of a piezo actuator, which applies strain to the SiC membrane as it stretches. (b) PL spectra as a function of $V_{\text{piezo}}$ (strain) at $T=20\mathrm{K}$, showing that the optical transitions of SiC defects can be tuned with strain. The applied strain splits the ZPL optical transitions, with the $c$ axis-oriented defects (PL1, PL2, and PL6) bifurcating and the basal-oriented defects (PL3, PL4, and PL5) trifurcating. (c) Polarization dependence of the PL from the strain-split ZPL branches, measured at the points indicated by purple circles in (b). The analyzed polarization is in the plane perpendicular to the $c$ axis.

Figure 2

(a) Strain sensing using dc ODMR of divacancy spins in SiC (${T_2}^{*}$ limited) at $T=20\mathrm{K}$. A strain-induced 0.8 MHz shift to the PL2 spin transition energies is observed, with the split peak within each curve due to a stray $B$ field of 0.35 G. (b) The Hahn-echo pulse scheme used for $T_2$-limited ac strain sensing. During the $t_{\text{free}}$ evolution periods, $\pm V_{\text{piezo}}$ pulses phase shift the spin superposition. The final pulse of the Hahn-echo sequence projects this phase onto a measurable spin population difference. (c) ac strain sensing data for the neutral divacancies, with $t_{\text{free}}=100\mu \mathrm{s}$, $t_{\text{pulse}}=80\mu \mathrm{s}$, $T=20\mathrm{K}$, and $B=0$. The fits are to single exponentially decaying sine curves and have frequencies of $0.07{\mathrm{V}}^{-1}$, $0.07{\mathrm{V}}^{-1}$, $0.12{\mathrm{V}}^{-1}$, and $0.16{\mathrm{V}}^{-1}$ for PL1–PL4, respectively. The three curves are offset from the origin for clarity.

Figure 3

(a) Electric-field sensing with divacancy and related spins in SiC. Using the same pulse sequence as in Fig. 2, but substituting $V_{\text{mem}}$ for $V_{\text{piezo}}$, $\pm V_{\text{mem}}$ pulses are applied across a $w=53\mu \mathrm{m}$ thick SiC membrane, using patterned electrodes that transmit light. As $V_{\text{mem}}$ is increased, $t_{\text{pulse}}$ is held constant at $80\mu \mathrm{s}$ (for the data at 20 K) or $20\mu \mathrm{s}$ (for the room-temperature data), and $B=0$. (b) ac electric field-sensing measurements for basal-oriented defects show mirror image $\Delta I$ oscillations when the higher (blue) and lower (orange) frequency spin-resonance transitions are used (left panel). The PL5 data (right panel) are taken at room temperature. (c) Electric field sensing for the $c$ axis oriented defects at 20 K, with the three curves vertically offset for clarity. The fits are to exponentially decaying sine curves, whose fitted frequencies are the spin-electric field coupling parameters (Table 1).

Figure 4

(a) A plot of the ZPL intensity of PL4 without microwave radiation (blue curve) and the change in PL when strong microwave irradiation is applied to the sample (grey curve). $\Delta I_{\text{mixed}}/I$ is measured to be $-0.10$, $+0.11$, $-0.14$, $-0.10$, $-0.24$, and $-0.22$ for PL1–PL6, respectively. (b) Time-resolved PL from PL4 as a function of delay from an excitation laser pulse (blue dots). The decay constant of the exponential fit (black) is the optical lifetime ($\tau$).$T=20\mathrm{K}$,$B=0$. See [30] for the calculation of $C_{\text{defect}}$ from $\Delta I_{\text{mixed}}/I$ and for the other defect species’ lifetimes and ODMR contrasts.