Manipulating thermal conductivity of silicon nanowires through surrounded fins and Ge dopant

Manipulating the phonon transport using nanotechnologies is one of the commonly adopted ways to reduce the thermal conductivity and enhance the thermoelectric performance of thermoelectric materials. In this work, we proposed a resonant structure, surrounded fins, for Si nanowires. The effects of both surrounded fins and Ge dopant on the thermal transport in Si NWs are studied using the molecular dynamics simulations. The root-mean-square (RMS) displacement, phonon dispersion, density of states and transmission function have been calculated to understand the thermal conductivity reduction in Si NWs. The calculated results show that both the surrounded fins and Ge dopants could significantly decrease the thermal conductivity of Si NWs. The thermal conductivity of finned Si NWs decreases with increasing the height of the surrounded fins. The more surrounded fins added, the more significant the thermal conductivity decreases. The thermal conductivity of SiGe NWs decreases initially and then increases with increasing Ge concentration. Through the analysis of RMS displacement and phonon dispersion, we found that surround fins could not only enhance anharmonicity by activating atoms near to the edge, but also increase the low frequency phonons and decrease the group velocities by modifying phonon dispersion relationship. The phonon transmission function suggests that the surrounded fins and Ge dopants would mainly suppress the transport of low-frequency and high-frequency phonons, respectively. Phonon transport in Si NWs could be suppressed over the whole frequency range by combining the surrounded fins and Ge dopants. Our results provide useful guidance in the design of efficient thermoelectric devices made of nanowires. (C) 2021 Elsevier Ltd. All rights reserved.