Effect of van der Waals interactions on the stability of SiC polytypes

Abstract

Density functional theory calculations with a correction of the long-range dispersion force, namely the van der Waals (vdW) force, are performed for SiC polytypes. The lattice parameters are in good agreement with those obtained from experiments.Furthermore, the stability of the polytypes in the experiments, which show 3C-SiC as the most stable, are reproduced by the present calculations. The effect of the vdW force on the electronic structure and the stability of polytypes are discussed. We observe that the vdW interaction is more sensitive to the cubic site than the hexagonal site. Thus, the influence of the vdW force increases with decreasing the hexagonality of the polytype, which results in the confirmation that the most stable polytype is 3C-SiC. † Present address: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan. 2Silicon carbide (SiC) has attracted great interest as a promising widegap material for use in power devices with low on-resistance because of its high breakdown field. SiC is also well known as a material with polytypism, such as 3C-, 2H-, 4H-, 6H-, 15R-SiC and so forth. Among the SiC polytypes, 4H-SiC has been desired for application in power devices because of its wide band gap and relatively isotropic electron mobility.Although the supply of 4H-SiC wafers with 6 inch size has begun, a large problem remains regarding the difficulty in selective growth of 4H-SiC. So far, many investigations have been performed for understanding the stability of the SiC polytypes experimentally 1,2) and theoretically. 3-7) However, the experimentally observed stability of the SiC polytypes, 1) which show 3C-SiC is more stable at less than 1873 K compared with 4H-, 6H-and 15R-SiC, has never been reproduced by a first principles density functional theory (DFT) calculation. In the DFT calculation, 4H-, 6H-or 15R-SiC is estimated to be the most stable among the typical polytypes. [4][5][6] The discrepancy has been proposed to arise from the entropic term and crystal growth conditions owing to the estimated total energy difference between 3C-and 4H-SiC, which denotes that the internal energy difference at 0 K is within a few meV. 4) However, the long-range dispersion force, that is, the van der Waals (vdW) force, has never been included in the 3 previous DFT calculations for SiC polytypes despite the observation that vdW often affects the electronic structure of covalent materials. 8) Recently, including the vdW force in DFT calculations, namely the DFT-D calculation, has been performed to describe the accurate electronic structure of two-dimensional layered structures and molecular crystals. [8][9][10][11][12] Although SiC is a highly covalent material, the effect of the vdW interaction on the stability of SiC polytypes has not been discussed so far. Herein, the stability of SiC polytypes are evaluated by the DFT-D calculation. The lattice parameters of the typical SiC polytypes are determined, and the effect of the ...

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

“…Hence, 3C-SiC turns out to be the most stable polytype. This is well in agreement both with experimental evidences inferring 3C-SiC as the most stable SiC structure in the nuclear stage [37] and with a recent theoretical work [29]. Nevertheless, the predicted energetic hierarchy at T=0K is still not sufficient to understand the competition in stability of SiC polytypes at higher temperature, as probed experimentally [16][17][18][19][20]27].…”

“…Recently it was shown that density functional theory (DFT) calculations [28] including the van der Waals (vdW) correction do predict the 3C phase to have the lowest free energy at T=0K [29]. This intriguing result points out the importance of considering long-range interactions when comparing different SiC polytypes.…”

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

“…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).…”

Transmission electron microscopy study of extended defect evolution and amorphization in SiC under Si ion irradiation

“…The polytypism arising from different stacking of the Si and C atomic layers is known to be a key factor in understanding the physical properties of SiC 4 . The cubic 3C‐SiC, with the so‐called β‐SiC crystal structure, is recognized as the most stable polytype, as confirmed by recent free energy calculations 5,6 . Moreover, the knowledge of extended defect formation such as stacking faults (SFs) and twins in the various polytypes is an important issue for use in electronic devices, since these defects can significantly modify the band structure and deteriorate their electronic properties 7,8 .…”

“…4 The cubic 3C-SiC, with the so-called β-SiC crystal structure, is recognized as the most stable polytype, as confirmed by recent free energy calculations. 5,6 Moreover, the knowledge of extended defect formation such as stacking faults (SFs) and twins in the various polytypes is an important issue for use in electronic devices, since these defects can significantly modify the band structure and deteriorate their electronic properties. 7,8 Moreover, 4H/6H SiC-based devices were found to degrade under operation due to partial Shockley SF formation and expansion.…”