Calculated elastic constants and deformation potentials of cubic SiC

Abstract

The full-potential linear-muffin-tin-orbital method in combination with the local-density-functional theory is used to calculate the equilibrium lattice constant, the cohesive energy, the bulk modulus and its pressure derivative, the elastic constants, the Kleinman internal displacement parameter \ensuremath{\zeta} the zone-center transverse-optical-phonon frequency, its Gr\"uneisen parameter and the corresponding energy-band strain, and optical-mode deformation potentials of cubic SiC. The results for equilibrium properties and the transverse-optical phonon at the center of the Brillouin zone are shown to be in good agreement with the available experimental data and previous first-principles calculations. The elastic constants of 3C-SiC are transformed to a trigonal symmetry tensor along the 〈111〉 direction, which allows a comparison to experimental data on hexagonal SiC. The agreement is found to be good. The elastic constants are also shown to be in good agreement with experimental data on the Young's and shear moduli and the Poisson ratio for polycrystalline SiC and with the Young's modulus of 3C-SiC whiskers along the 〈111〉 direction, which is related to the theoretical cleavage strength. Predictions are also made for the deformation potentials, which have not yet been measured. The discrepancies with previous atomic-sphere-approximation calculations for the trigonal strain and optical-mode deformation potentials indicate the importance of nonspherical terms in the potential for these deformations. The absolute deformation potential of the valence-band maximum is computed by means of a heterojunction calculation between strained and unstrained materials. This procedure is shown to give good agreement with previous calculations for Si.