Molecular Dynamics Simulation on Longitudinal Optical Phonon Mode Decay and Heat Transport in a Silicon Nano-Structure Covered with Oxide Films

Abstract

A series of molecular dynamics (MD) simulations have been conducted to investigate the heat transport in terms of the phonon dynamics in nanoscale silicon (Si). This work is motivated by a concern over the stagnation of heat at the drain region of nanoscopic transistors, owing to this, a large amount of optical phonons with a low group velocity are emitted from hot electrons, which are ballistically transferred through channel region. The point of this work is the explicit inclusion of the SiO 2 film in the MD simulation of the Si lattice. The calculation results show that longitudinal optical (LO) phonons decay faster as Si lattice thickness decreases and turn into acoustic phonons. In contrast, thermal diffusion rate decreases with Si lattice thickness. Both the decay rate of LO phonons and thermal diffusion rate are not governed by oxide thickness. These results imply that the phonon scattering at the SiO 2 /Si interface is enhanced by thinning the Si layer. In nanoscopic devices, a thin Si layer is effective in diminishing the optical phonons with a low group velocity, but it hinders the subsequent heat transport.

Phonon Dispersion in <100> Si Nanowire Covered with SiO2 Film Calculated by Molecular Dynamics Simulation

“…The bulk phonon Si dispersion relation shown in Fig. 3a agrees with that obtained by diagonalizing the dynamical matrix (11). In the bare SiNW, as shown in Fig.…”

Phonon Dispersion in 〈100〉 Si Nanowire Covered with SiO2Film Calculated by Molecular Dynamics Simulation

“…5,6,10 and 11. In our previous MD study, 21 it was found that the thermal energy diffusion process is retarded with thinning the Si core thickness and is less dependent on the outer SiO 2 film thickness. Therefore, it can be concluded that the increasing the surface-to-volume ratio of the inner SiNW by the oxidation is responsible for the thermal conductivity degradation.…”

“…In the practical NW, the SiO 2 film would modify the phonon energy dispersion, and thus phonon energy spectrum, group velocity and relaxation time, due to the oxide-induce strain and SiO 2 /Si interface roughness. 5,6,20,21 Therefore the insulating oxide film should be included in the simulation system.…”