  On the basis of detailed first-principles calculations the anisotropic
thermoelectric transport properties of biaxially strained silicon were studied
with focus on a possible enhancement of the powerfactor. Electron as well as
hole doping were examined in a broad doping and temperature range. In the
low-temperature and low-doping regime an enhancement of the powerfactor was
obtained for compressive and tensile strain in the electron-doped case and for
compressive strain in the hole-doped case. In the thermoelectrically more
important high-temperature and high- doping regime a slight enhancement of the
powerfactor was only found for the hole-doped case under small biaxial tensile
strain. The results are discussed in terms of band-structure effects. An
analytical model is presented to understand the fact that the thermopower
decreases if degenerate bands are energetically lifted due to a strain- induced
redistribution of states.
