  It is generally assumed in the thermoelectric community that the lattice
thermal conductivity of a given material is independent of the electronic
properties. This perspective is however questionable since the electron-phonon
coupling could have certain effects on both the carrier and phonon transport,
which in turn will affect the thermoelectric properties. Using SiGe compound as
a prototypical example, we give an accurate prediction of the carrier
relaxation time by considering scattering from all the phonon modes, as opposed
to the simple deformation potential theory. It is found that the carrier
relaxation time does not change much with the concentration, which is however
not the case for the phonon transport where the lattice thermal conductivity
can be significantly reduced by electron-phonon coupling at higher carrier
concentration. As a consequence, the figure-of-merit of SiGe compound is
obviously enhanced at optimized carrier concentration, and becomes more
pronounced at elevated temperature.
