2.2 Properties and Defect Study of 3C-SiC
Raman scattering measurements are performed on total 20 sites across the entire wafer surface. All spectra are nearly the same, only the peak at 796 cm-1 is present (Figures 2a, b). The peak is assigned to be the 3C-SiC’s transversal optical mode (TO).[32-34] Another characteristic mode, the longitudinal optical one (located at 975 cm-1), which is dependent on the carrier density, does not appear. No folded transverse optical modes at 776 and 707 cm-1 for 4H- and 6H-SiC are observed.[34, 35] A small peak (marked by an arrow) at 741 cm-1 are probably due to the stacking faults or stress.[32, 33] To obtain the information on the evolution of the transition from 4H to 3C, we conduct the Raman scattering measurements on a cross section of the grown boule and the results are shown in Figure 2b and Figure S3. It is clearly seen that the 3C occurs immediately at the upper surface of the seed, following a transition zone (TZ) about 20 μm consisting of both 3C and 4H. The single phase of 3C is maintained throughout the boule. The observation of photoluminescence (PL) at 523 nm (Figure 2c) corresponds well to the bandgap of 2.36 eV, further confirming the 3C polytype.
The boule surface is quite flat, but growth steps of 9~22 nm are clearly seen (Figure S4). Single crystal and powder X-ray diffraction results on small grains cracked from the boule confirm the polytype is 3C with refined lattice parameter a = 4.3563(4) Å (Figure S5 and Tables S1-2), similar to the previously reported results.[8] Plan-view high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) taken on a spherical aberration TEM (Figure 2d) clearly identifies Si and C atoms arrayed in a manner of ABC sequence. The selected area diffraction pattern shown in inset of Figure 2d along\(\left[1\overset{\overline{}}{1}0\right]\) zone axis (Z.A.) is well indexed based on a space group of F -43m. Electron energy loss spectrum (EELS) mapping results (Figure S6) indicate the homogeneous distribution of C and Si at a nanoscale level. Energy dispersive spectroscopy (EDS) mapping results also indicate the homogeneous distribution of Si, C and N (Figure S7).