Thermoelectric properties of monolayer GeAsSe and SnSbTe

We report electrical and thermal transport properties of monolayer GeAsSe and SnSbTe as determined by first principles electronic structure and transport calculations. These materials have an unusual combination of high Seebeck coefficient and conductivity for p-type doping. This is due to the complex non-parabolic electronic band structure, weak scattering due to small deformation potentials, and the reduced dimensionality of the monolayers. The combination of high Seebeck coefficient and high electrical conductivity for p-type doping leads to the large power factor, especially along the zigzag chain direction. In addition, from anharmonic phonon scattering calculations the phonon thermal conductivity is found to be low. This leads to high ZT values of approximately 4 and 6 for these two materials at 300 K. These materials thus provide a platform for demonstrating the expected and long-sought extremely high ZT arising from dimensional reduction.