Strain effect analysis on the thermoelectric figure of merit in n-type Si/Ge nanocomposites

In this paper, the effect of strain on the thermoelectric figure of merit is investigated in n-type Ge nanowire-Si host nanocomposite materials. The Seebeck coefficient and electrical conductivity of the Si-Ge nanocomposites are calculated using an analytical model derived from the Boltzmann transport equation (BTE) under the relaxation-time approximation. The effect of strain is incorporated into the BTE through the strain induced energy shift and effective mass variation calculated from the deformation potential theory and a degenerate k . p method at the zone-boundary X point. The effect of strain on the phonon thermal conductivity in the nanocomposites is computed with a model combining the strain dependent lattice dynamics and the ballistic phonon BTE. The electronic thermal conductivity is computed from the electrical conductivity using the Wiedemann-Franz law. Normal and shear strains are applied in the transverse plane of the Si-Ge nanocomposites. Thermoelectric properties, including the electrical conductivity, thermal conductivity, Seebeck coefficient, and dimensionless figure of merit, are computed for Si-Ge nanocomposites under these strain conditions. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3693307]