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arXiv · 1012.1054

Tuning lattice thermal conductance by porosity control in ultra-scaled Si and Ge nanowires

Abhijeet Paul·Gerhard Klimeck
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Abstract

Porous nanowires (NWs) with tunable thermal conductance are examined as a candidate for thermoelectric (TE) devices with high efficiency (ZT). Thermal conductance of porous Si and Ge NWs is calculated using the complete phonon dispersion obtained from a modified valence force field (MVFF) model. The presence of holes in the wires break the crystal symmetry which leads to the reduction in ballistic thermal conductance ($σ_{l}$). $[100]$ Si and Ge NWs show similar percentage reduction in $σ_{l}$ for the same amount of porosity. A 4nm $\times$ 4nm Si (Ge) NW shows $\sim$ 30% (29%) reduction in $σ_{l}$ for a hole of radius 0.8nm. The model predicts an anisotropic reduction in $σ_{l}$ in SiNWs, with $[111]$ showing maximum reduction followed by $[100]$ and $[110]$ for a similar hole radius. The reduction in $σ_{l}$ is attributed to phonon localization and anisotropic mode reduction.

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Abhijeet Paul, Gerhard Klimeck. 2010-12-07. Tuning lattice thermal conductance by porosity control in ultra-scaled Si and Ge nanowires. https://doi.org/10.1063/1.3556648

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