Atomistic calculations of the electronic, thermal, and thermoelectric properties of ultra-thin Si layers
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Low-dimensional semiconductors are considered promising candidates for thermoelectric applications with enhanced performance because of a drastic reduction in their thermal conductivity, κ l , and possibilities of enhanced power factors. This is also the case for traditionally poor thermoelectric materials such as silicon. This work presents atomistic simulations for the electronic, thermal, and thermoelectric properties of ultra-thin Si layers of thicknesses below 10 nm. The Linearized Boltzmann theory is coupled: (i) to the atomistic sp3d5s∗ tight-binding (TB) model for the electronic properties of the thin layers, and (ii) to the modified valence-force-field method (MVFF) for the calculation of the thermal conductivity of the thin layers. We calculate the room temperature electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, and ZT figure of merit of ultra-thin p-type Si layers (UTLs). We describe the numerical formulation of coupling TB and MVFF to the linearized Boltzmann transport formalism. The properties of UTLs are highly anisotropic, and optimized thermoelectric properties can be achieved by the choice of the appropriate transport and confinement orientations, as well as layer thickness.
KeywordsThermoelectrics Tight-binding sp3d5s∗ Modified valence-force-field Boltzmann transport Seebeck coefficient Thermoelectric power factor Silicon ultra-thin layers ZT figure of merit
The work leading to these results has received funding from the European Community’s Seventh Framework Programme under grant agreement no. FP7-263306, and the Austrian Science Fund (FWF), grant P25368-N30.
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