Modeling phonon transport in nanowires with rough surfaces

We study phonon transmission in thin silicon nanowires where surface-roughness dominates over bulk disorder. Our previous study was based on an exact mapping of surface disorder, modeled as a random distribution of localized phonons¹. Here we extend the idea to study its effects on transport of propagating acoustic phonons.We characterize the localized phonons by surface roughness parameters and study the effects using NEGF techniques. Non-linear heat current is evaluated for various couplings between the propagating phonons from the leads and the localized phonon in the central device. Numerical evaluation gives frequency dependence of heat current at various finite temperatures, where the difference in temperature between the two leads can be large under non-equilibrium conditions. We show that our simple model captures the qualitative features obtained in experiments, and suggests combination of surface parameters that can lead to a substantial reduction in thermal conductivity, as required for applications in thermoelectricity.

Reference: (1) https://doi.org/10.1103/PhysRevB.96.075403