Thermoelectric enhancement in PbTe with K or Na codoping from tuning the interaction of the light- and heavy-hole valence bands

The effect of K and K-Na substitution for Pb atoms in the rocksalt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power. We combined high-temperature Hall-effect, electrical conductivity, and thermal conductivity measurements to show that K-Na codoping do not form resonance states but can control the energy difference of the maxima of the two primary valence subbands in PbTe. This leads to an enhanced interband interaction with rising temperature and a significant rise in the thermoelectric figure of merit of p-type PbTe. The experimental data can be explained by a combination of a single- and two-band models for the valence band of PbTe depending on hole density that varies in the range of 1--1510^19 cm^-3.