Thermoelectric transport properties of borophane

Abstract

We theoretically study the influence of impurity scattering on the electric and thermal transport of borophane layer, a two-dimensional anisotropic Dirac semi-metal with two tilted and anisotropic Dirac cones. In a systematic framework, we have calculated exactly the electrical conductivity and thermoelectric coefficients of borophane in the presence of the short-range, long-range charged impurity and the short-range electro-magnetic (SREM) scatterers, by using the exact solution of the Boltzmann transport equation within the linear-response theory. Contrary to the large electron-hole asymmetry in borophane, its electron-hole conductivity is nearly symmetric. Interestingly, for the short-range scatters, just like graphene, the short-range conductivities of borophane have the constant values, independent of the chemical potential, while the conductivities of the SREM scatterers are linearly dependent on the chemical potential. Regardless of the impurity type, the electric conductivity of borophane is highly anisotropic, while the Seebeck coefficient and figure of merit (${\it ZT}$) are isotropic. Along with the ambipolar nature of the borophane thermopower, a very high value of ${\it ZT}$ around unity is obtained at room temperature, due to the large asymmetry between electrons and holes in borophane. More importantly, borophane attains its maximum value of ${\it ZT}$ at very low chemical potentials, in the vicinity of the charge neutrality point. In comparison to phosphorene, a highly unique anisotropic 2D material, borophane with a higher anisotropy ratio ($σ_{xx}/σ_{yy}\sim10$), is an unprecedented anisotropic material. This high anisotropy ratio together with the large figure of merit, suggest that borophane is promising for the thermoelectric applications and transport switching in the Dirac transport channels.