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).