Electronic structure and thermoelectric properties of monolayers of group V atoms

Quantum confinement effects in narrow band gap semiconductors tend to enhance their thermoelectric properties. In the extreme limit of 2 dimensional (2D) confinement, the observation of massless Dirac particles associated with low energy excitations of honeycomb (HC) lattices of group IV atoms (C, Si, Ge, Sn) near the Dirac points (DPs) and spin-orbit interaction (SOI) induced gaps at the DPs have led to extensive study of the physical properties of these 2D monolayer systems. In this paper we discuss the electronic structure of 2D HC lattices of group V atoms (As, Sb, Bi) with a focus on their thermoelectric properties, particularly their thermopower. We find DPs at the K points of the Brillouin zone for both planar (flat) and puckered sheets. Unlike the group IV systems the Fermi energy in group V systems lies above the DPs. The flat sheets are metallic but undergo structural distortions to form puckered sheets that are semiconducting. SOI profoundly alters their band structure, opens up gaps at the DPs, and in binary systems BiSb and SbAs gives large Rashba-type spin splitting. Monolayers of group V atoms show excellent thermoelectric properties, particularly in the hole-doped regime.