Effects of Polytypism on the Thermoelectric Properties of Group-IV Semiconductor Nanowires: A Combination of Density Functional Theory and Boltzmann Transport Calculations

The effects of polytypism on thermoelectric properties of Si and Ge nanowires (NWs) are systematically investigated by using a combination of density functional theory and Boltzmann transport calculations. The calculations for NWs with various polytypes demonstrate that the thermoelectric figure of merit ZT of Si and Ge NWs can be tuned by changing different stacking sequences along the growth direction. In particular, the ZT values of n-type Si and Ge NWs with hexagonal (2H) structure at 300 K are significantly larger than ZT of Si and Ge NWs with a cubic (3C) structure. The underlying mechanism for the enhanced ZT value in Si NWs with a 2H structure compared with a 3C structure is attributed by the different Seebeck coefficient depending on the structure, while that in Ge NWs is due to the difference in both the Seebeck coefficient and electrical conductivity. The calculated results offer a way to design high-performance thermoelectric materials by controlling the polytype of NWs.