  By using first-principles tight-binding electronic structure calculation and
Boltzmann transport equation, we investigate the size dependence of
thermoelectric properties of silicon nanowires (SiNWs). With cross section area
increasing, the electrical conductivity increases slowly, while the Seebeck
coefficient reduces remarkably. This leads to a quick reduction of cooling
power factor with diameter. Moreover, the figure of merit also decreases with
transverse size. Our results demonstrate that in thermoelectric application, NW
with small diameter is preferred. We also predict that isotopic doping can
increase the value of ZT significantly. With 50% 29Si doping (28Si0.529Si0.5
NW), the ZT can be increased by 31%.
