Understanding the anisotropic phonon thermal transport through 2D β-siligraphene

Low dimensional and 2D materials have been considered as promising candidates for thermoelectric applications due to their intrinsic high carrier mobilities. Amongst them, β-SiC₇ has gained interest due to its direct band gap and thermal stability. To further explore the potential of this material, we present a detailed analyses of the lattice thermal conductance (κ_L) of 2D β-SiC₇ through a full iterative solution of the Boltzmann transport equation. We find the thermal transport to be anisotropic with κ_yy = 97.62 (10⁻⁹ W/K), significantly lower than that of graphene due to the presence of Si atom in the lattice which causes distortion and weakening of the acoustic branches. The TA and LA modes to possess the highest phonon group velocities due to their linear nature around the Γ point in the phonon dispersion, while the ZA mode possesses the lowest group velocity as a result of the quadratic shape of the branch within the vicinity of the Γ point. On the other hand, the flexural ZA branch possesses the longest carrier lifetime that is about three orders of magnitude higher than the LA and TA branches, since the mass disorder in the lattice softens the acoustic modes. The thermodynamic limit to the κ_L is attained for a sample domain size of ∼45 μm and nanostructuring emerges as a possibility to reduce the κ_L by 50% to enhance the thermoelectric efficiency of the material.