Size-dependent thermoelectricity in nanowires

By employing a semiclassical Boltzmann transport equation and using an energy and size-dependent relaxation time (tau) approximation (RTA), we evaluate the thermoelectric figure-of-merit ZT of a quantum wire with rectangular cross-section. The inferred ZT shows abrupt enhancement in comparison with its counterparts in bulk systems. Still, the estimated ZT for the representative Bi2Te3 nanowires and its dependence on wire parameters deviate considerably from those predicted by the existing RTA models with a constant tau. In addition, we address contribution of the higher energy subbands to the transport phenomena, the effect of chemical potential tuning on ZT, and correlation of ZT with quantum size effects (QSEs). Particularly, we show that within each subband, ZT has an optimum value which depends on wire dimensions and chemical potential. The obtained results are of general validity for a wide class of systems and may prove useful in the ongoing development of the modern thermoelectric applications.