Temperature-Dependent Stability of Polytypes and Stacking Faults inSiC: Reconciling Theory and Experiments

Abstract

The relative stability of SiC polytypes, changing with temperature, has been considered a paradox for about thirty years, due to discrepancies between theory and experiments. Based on ab-initio calculations including van der Waals corrections, a temperature-dependent polytypic diagram consistent with the experimental observations is obtained. Results are easily interpreted based on the influence of the hexagonality on both cohesive energy and entropy. Temperature-dependent stability of stacking faults is also analyzed and found to be in agreement with experimental evidences. Our results suggest that lower temperatures during SiC crystal deposition are advantageous in order to reduce ubiquitous stacking faults in SiC-based power devices.

Characterization of 4H- and 6H-Like Stacking Faults in Cross Section of 3C-SiC Epitaxial Layer by Room-Temperature μ-Photoluminescence and μ-Raman Analysis

“…Thus, we think that the area of the µ-Raman map (reported in Figure 4b) characterized by the presence of the peak at 778.3 cm −1 is an area with a high density of defects. In particular, these extrinsic stacking faults recall the structure of the 4H-SiC [15]. In the same way, the TO mode for 6H-SiC lattice shows two components at 764.4 cm −1 and 789.4 cm −1 [17].…”

“…In the same way, the TO mode for 6H-SiC lattice shows two components at 764.4 cm −1 and 789.4 cm −1 [17]. Thus, it is possible that the area of the µ-Raman map (reported in Figure 4c) characterized by the presence of the peak at 784 cm −1 is an area with a high density of double-extrinsic stacking fault, which recall the structure of the 6H-SiC [15]. The component at 764.4 cm −1 cannot be discriminated in our spectra because it is too close to signals from the laser.…”

“…In particular, the formation energies of SFs in 3C-SiC decrease with the temperature (particularly for ESFs). Even though 6H-like SF shows a lower formation energy than 4H-like [15], and it is considered the most common inclusion of other polytypes in 3C-SiC [25], we clearly observe the peak related to the presence of 6H-like SFs only in the first 15 µm of the film (from the removed Si interface to the surface, Figure 4c). Meanwhile, it was possible to detect the peak attributable to 4H-like SFs in the first 20-25 µm of the film (Figure 4b).…”

“…The average Raman spectra acquired in regions (1), (2), and (3) were reported in Figure 4d an intrinsic, extrinsic, and double-extrinsic stacking fault. SFs are wrong sequences of the double layers and they can be seen as inclusions of a few layers of an SiC polytype in the perfect layer stacking of another polytype [15]. It is known that the TO mode for 4H-SiC lattice is located at 778 cm −1 [16].…”

“…The literature on the thermodynamic stability and polytypes of SiC is rich. Many theoretical works were carried out to explain the band structure and total energies of the various polytypes of silicon carbide [22][23][24], showing that, at a high temperature, the 6H-and 4H-SiC polytypes become thermodynamically more stable than 3C-SiC [15]. In particular, the formation energies of SFs in 3C-SiC decrease with the temperature (particularly for ESFs).…”