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

Abstract

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.