Theoretical study on geometry and temperature effects of thermoelectric properties of Si and Ge nanowires

Thermoelectric properties of Si and Ge nanowires are studied theoretically using sp³d⁵s* tight-binding and ballistic transport approach. We found that the Seebeck coefficient and power factor per area depend on the nanowire size and its orientation. In addition, for nano-scale nanowires, cross-sectional shape effect is considerable and transmission mode dominates the performance. Temperature also has a great impact on the thermoelectric performance of nanowires. The power factor of Si nanowires along different orientations is approaching to the same value as temperature growing higher than 300 K; while power factor of Ge nanowires along [100] is the largest at high temperature, but the smallest at extreme low temperature.