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).