Large thermoelectric figure of merit in Si1−xGex nanowires

By using first-principles electronic structure calculation and Boltzmann transport equation, we investigate composition effects on the thermoelectric properties of silicon-germanium (Si1−xGex) nanowires (NWs). The power factor and figure of merit in n-type Si1−xGex wires are much larger than those in their p-type counterparts with the same Ge content and doping concentration. Moreover, the maximal obtainable figure of merit can be increased by a factor of 4.3 in n-type Si0.5Ge0.5 NWs, compared with the corresponding values in pure silicon nanowires (SiNWs). Given the fact that the measured ZT of n-type SiNW is 0.6∼1.0, we expect ZT value of n-type Si1−xGex NWs to be 2.5∼4.0.