Optimizing thermoelectric efficiency of superlattice nanowires at room temperature

It is known that the figure of merit ($ZT$) of thin nanowires can be significantly enhanced at room temperature due to the reduction of phonon thermal conductance arising from the increase of boundary scattering of phonons. It is expected that the phonon thermal conductance of nanowires filled with quantum dots (QDs) will be further reduced. Here we consider a superlattice nanowire (SLNW) modeled by a linear chain of strongly coupled QDs connected to electrodes. We study the dependence of $ZT$ on the QD energy level ($E_0$) (relative to the Fermi level $E_F$ in the electrodes), inter-dot coupling strength ($t_c$), tunneling rate ($\Gamma$), and temperature $T$ in order to optimize the design. It is found that at room temperature the maximum power factor occurs when $(E_0-E_F)/k_BT \approx 2.4$ and $\Gamma=t_c$, a result almost independent of the number of QDs in SLNW as long as $t_c/k_BT <0.5$. By using reasonable physical parameters we show that thin SLNW with cross-sectional width near $3~nm$ has a potential to achieve $ZT\ge3$.