Anisotropic thermoelectric effect on phosphorene and bismuthene: first-principles calculations based on nonequilibrium Green’s function theory

Abstract

By using the nonequilibrium Green’s function (NEGF) method, we perform first-principles calculations for phosphorene and bismuthene and evaluate their thermoelectric properties on the basis of the Landauer formalism. We find that the figures of merit strongly depend on the transport direction: the figures for the zigzag (ZZ) direction are substantially different from those for the armchair direction. These anisotropies are found to originate from the difference between the transmission functions in the AM and ZZ directions. We find that p-type bismuthene has a large figure of merit when the transport is in the ZZ direction, then we conclude that bismuthene has some advantages over phosphorene as a thermoelectric material. We also clarify that the spin–orbit coupling has a substantial effect on the thermoelectric properties of bismuthene.