Identification of a Frenkel-pair defect in electron-irradiated 3$C$ SiC

An electron paramagnetic resonance (EPR) spectrum labeled LE1 was observed in $n$-type 3C SiC after electron irradiation at low temperatures $\left(\sim 80–100\text{K}\right)$. A hyperfine interaction with four nearest C neighbors similar to that of the well-known silicon vacancy in the negative charge state was observed, but the LE1 center has a lower symmetry, ${\text{C}}_{2\text{v}}$. Supercell calculations of different configurations of silicon vacancy-interstitial Frenkel-pairs, ${\text{V}}_{\text{Si}}{\text{-Si}}_{\text{i}}$, were performed showing that pairs with a nearest neighbor Si interstitial are unstable—${\text{V}}_{\text{Si}}$ and ${\text{Si}}_{\text{i}}$ will automatically recombine—whereas pairs with a second neighbor ${\text{Si}}_{\text{i}}$ are stable. Comparing the data obtained from EPR and supercell calculations, the LE1 center is assigned to the Frenkel-pair between ${\text{V}}_{\text{Si}}$ and a second neighbor ${\text{Si}}_{\text{i}}$ interstitial along the [100] direction in the $3+$ charge state, ${\text{V}}_{\text{Si}}^{-}{\text{-Si}}_{\text{i}}^{4+}$. In addition, a path for the migration of ${\text{Si}}_{\text{i}}^{4+}$ was found in 3C SiC. In samples irradiated at low temperatures, the LE1 Frenkel-pair was found to be the dominating defect whereas EPR signals of single vacancies were not detected. The center disappears after warming up the samples to room temperature.

Figure 1

(Color online) EPR spectra in 3C SiC after electron irradiation at $\sim 80–100\text{K}$ measured at 28 K under white light illumination for (a) $\mathbf{B}\parallel \left[100\right]$, (b) $\mathbf{B}\parallel \left[111\right]$, and (c) $\mathbf{B}\parallel \left[011\right]$. The insets show the hf structures due to the interaction with the four nearest C neighbors. The insert in (c) is a scaled up part from the same spectrum showing also lower magnetic-field regions with a different scale.

Figure 2

(Color online) EPR spectra in 3C SiC measured for $\mathbf{B}\parallel \left[100\right]$ before (a–b) and after (c–d) warming up the sample to room temperature $\left(\sim 300\text{K}\right)$. All the spectra were measured with the same parameters and microwave power.

Figure 3

Angular dependence of the LE1 spectrum in 3C SiC with the magnetic field rotating in the $\left(0\overline{1}1\right)$ plane. The dotted curves represent the simulated angular dependence using the parameters in Table and the spin-Hamiltonian Eq. (7).

Figure 4

The angular dependence of the ${}^{13}\text{C}$ hf splittings of the LE1 center measured with $\mathbf{B}$ rotating in the $\left(0\overline{1}1\right)$ plane.

Figure 5

(Color online) The defect model for the LE1 center: the Si vacancy-interstitial Frenkel-pair with the second neighbor ${\text{Si}}_{\text{i}}$ at TC site along the [100] direction. The open circle denotes the vacant site. The selected isosurface of the calculated spin density is also shown: it is mainly localized on the four nearest C neighbors of the vacancy.