Identification of antisite carbon split-interstitial defects in $4H\text{-SiC}$

A rich variety of optical centers with high energy local vibrational modes has been found in electron-irradiated $4H\text{-SiC}$ in both the as-irradiated and annealed states. These energies have been measured and the annealing dependence of the optical centers has been investigated by low-temperature photoluminescence spectroscopy. In view of the relatively high energies of these modes, it is anticipated that they involve carbon interstitials and a detailed correlation has therefore been undertaken, in selected cases, between the experimentally observed energies and those calculated by recent local density approximation, i.e., ab initio methods for atomic arrangements involving carbon interstitials. When satisfactory agreement has been achieved, the annealing behavior is compared to the calculated stabilities of the defects concerned. As a result, different configurations of carbon antisite defects are identified together with their spatial distributions with respect to the irradiated areas and their sequences of appearance and disappearance on annealing. These findings significantly add to the understanding of the radiation damage process and its subsequent development and recovery on annealing. Some of the optical centers that have well-defined local vibrational modes remain to be identified in the future.

Figure 1

(Color online) Dependence of the ZPLs in Table on annealing for one particular sample [Al doped, $N_A\text{−}{N}_D$ ($7.0\times {10}^{15}{\text{cm}}^{-3}$), without donor-acceptor pair emission, with thickness of $36.4\mu \text{m}$, with dose of ${10}^{20}e{\text{cm}}^{-2}$]. Extra lines added include the alphabet lines $a\text{−}d$, the Si vacancy $\left(V_1\right)$, and the 673 nm ZPL. The $x$ on the 520.6 nm ZPL indicates that the result comes from a different sample. Results were obtained by using both 325 nm and 488 nm excitation. The graphs have been scaled as indicated. The PL results were obtained at a sample temperature of $\sim 7\text{K}$.

Figure 2

Spectrum of the tricarbon antisite defect in $4H\text{-SiC}$. The three LVMs (LM1, LM2, and LM3) are repeated as sum modes in the second order spectrum (2). It was acquired at $\sim 7\text{K}$ by using 325 nm laser excitation.

Figure 3

Spectrum of the 493.5 nm center interpreted here as the $k{h}_{,\text{hex}}$ dicarbon antisite pair in $4H\text{-SiC}$. In this case, the coupling is so strong that two orders of sum modes are clearly visible as indicated by the numbers below the curve. The spectrum was acquired at $\sim 7\text{K}$ by using 325 nm laser excitation.

Figure 4

(Color online) Detail of the LM local mode of the 493.5 nm center illustrated in Fig. 5. Deconvolution of the spectrum has been performed, as shown in the inset, to determine the energy of the considerably weaker side band (LM’) on the short wavelength side of LM. The spectrum was acquired over 15 min at $\sim 7\text{K}$ by using 325 nm laser excitation.

Figure 5

(Color online) Line scans of PL intensity variations across two $100\mu \text{m}$ diameter electron-irradiated areas of a sample. The $c/d$ spectra were acquired after a $300°\text{C}$ anneal and the $D_{\text{I}}$ spectrum was acquired from the same region after a $1200°\text{C}$ anneal. The spectra were obtained at $\sim 7\text{K}$ by using 325 nm laser excitation.

Figure 6

(Color online) Figures comparing the ZPL integrated intensity distributions across two $100\mu \text{m}$ diameter irradiated areas observed for different optical centers by using 325 and 488 nm laser excitations at $\sim 7\text{K}$. The irradiations on the left side of the figures were performed at 300 keV, on the right at 250 keV; the dose was ${10}^{20}e{\text{cm}}^{-2}$ in each case. (a) ZPL of 450.6 nm for a sample annealed to $1100°\text{C}$; note the drop off of intensity in the irradiated region and the spread of intensity outside it for 325 nm excitation. (b) ZPL of 471.8 nm for a sample annealed at $1200°\text{C}$; note the similarity of the results at the two wavelengths.

Figure 7

(Color online) Figures illustrating the changes in integrated intensity of specified ZPLs as a consequence of exposure to an intense 325 nm beam at $\sim 7\text{K}$. The results come from the periphery of the irradiated regions and the intensity profiles were obtained by using the low-power (25 times reduction) 325 nm excitation $\sim 7\text{K}$ along a line perpendicular to the linear trajectory of the intense 325 nm beam. (a) Enhancement of 463 nm intensity and reduction of 471.8 and 493.5 nm intensities for a sample annealed at $1300°\text{C}$. (b) Enhancement of 463 nm intensity and reduction of 493.5 nm intensity for a sample annealed at $1000°\text{C}$.