Understanding heat conduction in defective silicon is crucial for electronics and thermoelectrics. Conventional understanding relies on the phonon gas picture, treating defects as scattering centers that reduce phonon lifetimes without altering frequencies and group velocities. We go beyond the phonon gas picture by employing the Wigner transport equation to investigate heat conduction in vacancy-defective silicon. Our findings reveal that, while thermal conduction in pristine silicon stems mainly from particlelike propagation of vibrational modes, wavelike tunneling becomes increasingly important 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 anharmonicity-renormalized 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 insights into thermal conduction in defective materials.

Close

PrevNext

View figure in article

• Anharmonic lattice dynamics
• Lattice thermal conductivity
• Silicon vacancies
• Diamond structure
• Elemental semiconductors
• Single crystal materials
• Molecular dynamics