ICT2014 Abstracts

As recent advances in nanostructured thermoelectric materials significantly lowered the lattice thermal conductivity close to the amorphous limit, suppression of electronic thermal conductivity including the bipolar contribution is now crucial to further reduce the total thermal conductivity for enhanced thermoelectric figure of merit. In this work we present theoretically that the thermoelectric figure of merit for a semiconductor material with a small band gap can be significantly enhanced near the intrinsic doping regime at high temperatures via the suppression of bipolar thermal conductivity when the minority carriers are effectively blocked by heterostructure barriers. The hetero-barriers can be either planar as in superlattices, or nonplanar as in a bulk material with embedded nanoparticles. We present enhancement in the figure of merit by the minority carrier blocking scheme for various thermoelectric materials such as PbTe, Mg₂Si_1-xSn_x, and ErSb:InGaSb nanocomposites. For example, we show that a zT ~ 2.0 for n-type PbTe and a zT ~ 3.6 for p-type PbTe are possible at 900 K with minority carrier blocking, when the lattice thermal conductivity is as low as 0.3 W/mK.  Finally, we compare the proposed minority carrier blocking scheme with the carrier energy filtering theory as two promising strategies for a large figure of merit enhancement.