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

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 (${\sigma }_l$). $[100]$ Si and Ge NWs show similar percentage reduction in ${\sigma }_l$ for the same amount of porosity. A 4nm $\times$ 4nm Si (Ge) NW shows $\sim$ 30% (29%) reduction in ${\sigma }_l$ for a hole of radius 0.8nm. The model predicts an anisotropic reduction in ${\sigma }_l$ in SiNWs, with $[111]$ showing maximum reduction followed by $[100]$ and $[110]$ for a similar hole radius. The reduction in ${\sigma }_l$ is attributed to phonon localization and anisotropic mode reduction.

3 Pages, 4 figures, submitted to Applied Physics Letters

References in corpus (1)

• Remarkable Reduction of Thermal Conductivity in Silicon Nanotubes

Cited by in corpus (2)

• Impacts of Atomistic Coating on Thermal Conductivity of Germanium Nanowires
• Shape and orientation effects on the ballistic phonon thermal properties of ultra-scaled Si nanowires