Thermoelectric properties of superlattice nanowires

We report here on a theoretical model for the electronic structure and transport properties of superlattice nanowires, considering their cylindrical wire boundary and multiple anisotropic carrier pockets. The thermoelectric properties of superlattice nanowires made of various lead salts (PbS, PbSe, and PbTe) are investigated as a function of the segment length, wire diameter, crystal orientation along the wire axis, and the length ratio of the constituent nanodots of the superlattice, based on the Kronig-Penney potential for each one-dimensional (1D) subband and on the 1D Boltzmann transport equations. A potential barrier--well inversion induced by quantum confinement, which is a unique phenomenon in superlattice nanowires, is predicted as the wire diameter decreases. $\mathrm{ZT}$ values higher than 4 and 6 are predicted for 5-nm-diameter PbSe/PbS and PbTe/PbSe superlattice nanowires at 77 K, respectively. These ZT values are significantly larger than those of their corresponding alloy nanowires, indicating that superlattice nanowires are promising systems for thermoelectric applications.