Lorenz function of Bi${}_2$Te${}_3$/Sb${}_2$Te${}_3$ superlattices

Combining first principles density functional theory and semi-classical Boltzmann transport, the anisotropic Lorenz function was studied for thermoelectric Bi${}_2$Te${}_3$/Sb${}_2$Te${}_3$ superlattices and their bulk constituents. It was found that already for the bulk materials Bi${}_2$Te${}_3$ and Sb${}_2$Te${}_3$, the Lorenz function is not a pellucid function on charge carrier concentration and temperature. For electron-doped Bi${}_2$Te${}_3$/Sb${}_2$Te${}_3$ superlattices large oscillatory deviations for the Lorenz function from the metallic limit were found even at high charge carrier concentrations. The latter can be referred to quantum well effects, which occur at distinct superlattice periods.