Figure 4. In-situ measurements of contact angles and
surface tension of melts. High temperature contact angle of melt droplet
of Melt 4 on a) 3C-SiC (111) surface and b) semi-insulated 4H-SiC (0001)
surface. The average contact angles are 40.38° ± 0.64° and 45.55° ±
0.07°, respectively. c) Measurement of surface tension of Melt 4 via
intravenous drip method. d) Histogram of surface tension (upper panel),
high temperature contact angles on 3C-SiC (111) and 4H-SiC (0001) planes
(lower panel), the solid-liquid interfacial energy difference between
melt and 4H-SiC (0001) and 3C-SiC (111) surface (middle panel) of Melt
4. The measurements are carried out at 1850 ℃ under \(p_{N_{2}}\) of 0
(Melt 1), 10 (Melt 2), 15 (Melt 3) and 20 kPa (Melt 4) with the total
growth pressure of 50 kPa.
It is easily obtained that the interfacial energies for 3C and 4H are\(\sigma_{3C/Melt\ 4}=\) 2151.11 ± 21.90 mN/m and\(\sigma_{4H/Melt\ 4}=\) 2390.89 ± 19.50 mN/m (Table S9), where\(\mathrm{\sigma}_{\mathrm{\text{SiC}}}\) is estimated from the results
in Ref. 28. Figure 4d shows the variations of melt surface tension, the
contact angles of melt on substrates and the calculated interfacial
energy between the melt and 3C-(111) and 4H-(0001) single crystals based
on Young’s equation with\(p_{N_{2}}\) measured for many
times (Figures S14-15). The melt’s surface tension decreases as
increasing \(p_{N_{2}}\), which can be attributed to the dissolved N in
the melt (Figure S16). We can see that interfacial energy between the
melt and 3C-(111) is lower than that for 4H-(0001), and their difference
widens with the increasing \(p_{N_{2}}\). Our results indicate that
other polytype inclusions are present when the \(p_{N_{2}}\) is below 15
kPa. Optimal pressures of \(p_{N_{2}}\) above 15 kPa are required to
stabilize the 3C polytype during the growth due to the much smaller
3C-/melt interfacial energy. We then regrow the crystal on a 3C-SiC seed
using the same compositions of flux under 20 kPa N2again. Raman scattering measurements confirm the 3C polytype (Figure
S17).