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We use first-principles electronic structure methods to calculate theelectronic thermoelectric properties (i.e. due to electronic transport only) ofsingle-crystalline bulk $n$-type silicon-germanium alloys vs Ge composition,temperature, doping concentration and strain. We find excellent agreement toavailable experiments for the resistivity, mobility and Seebeck coefficient.These results are combined with the experimental lattice thermal conductivityto calculate the thermoelectric figure of merit $ZT$, finding very goodagreement with experiment. We predict that 3% tensile hydrostatic strainenhances the $n$-type $ZT$ by 50% at carrier concentrations of $n=10^{20}$cm$^{-3}$ and temperature of $T=1200K$. These enhancements occur at differentalloy compositions due to different effects: at 50% Ge composition theenhancements are achieved by a strain induced decrease in the Lorenz number,while the power factor remains unchanged. These characteristics are importantfor highly doped and high temperature materials, in which up to 50% of the heatis carried by electrons. At 70% Ge the increase in $ZT$ is due to a largeincrease in electrical conductivity produced by populating the high mobility$\Gamma$ conduction band valley, lowered in energy by strain.

journal of applied physics

Enhancement of the electronic thermoelectric properties of bulk strained  silicon-germanium alloys using the scattering relaxation times from first  principles