Revisiting the Mechanisms of Thermal Transport in Vacancy-Defective Silicon

TL;DR

This paper investigates heat conduction in vacancy-defective silicon using the Wigner transport equation, revealing wave-like tunnelling and the significant impact of vacancies on velocity operators, challenging traditional phonon scattering models.

Contribution

It introduces a wave-based approach to understand thermal transport in defective silicon, highlighting the role of vacancies in reducing velocities and altering anharmonic effects, beyond conventional phonon scattering theories.

Findings

Wave-like tunnelling becomes significant with vacancies.

Vacancies reduce velocity operators more than phonon lifetimes.

Anharmonic effects on thermal conductivity weaken and reverse with vacancy concentration.

Abstract

Understanding heat conduction in defective silicon is crucial for electronics and thermoelectrics. Conventional understanding relies on phonon gas picture, treating defects as scattering centers that reduce phonon lifetimes without altering frequencies and group velocities. We go beyond phonon gas picture by employing Wigner transport equation to investigate heat conduction in vacancy-defected silicon. Our findings reveal that while thermal conduction in pristine silicon stems mainly from particle-like propagation of vibrational modes, wave-like tunnelling becomes increasingly significant in the presence of vacancies. Contrary to the conventional belief that defects only perturb mode lifetimes, we demonstrate that vacancies also diminish velocity operators, a dominant factor in thermal conductivity reduction, surpassing even the effect of lifetime shortening. Furthermore, incorporating anharmonic frequencies and interatomic force constants shows that while anharmonicity suppresses thermal conductivity in pristine silicon, this effect weakens with vacancy concentration and reverses to enhance conductivity. These findings challenge conventional knowledge and provide new insights into thermal conduction in defective materials.