Combined treatment of phonon scattering by electrons and point defects explains the thermal conductivity reduction in highly-doped Si

TL;DR

This study combines first-principles calculations of phonon scattering by electrons and point defects to explain the observed reduction in thermal conductivity in highly doped silicon, emphasizing the importance of both mechanisms.

Contribution

It introduces a comprehensive model that accounts for both electron and point defect scattering, accurately matching experimental data across doping levels and temperatures.

Findings

Electron scattering dominates at low doping and temperature.

Point defect scattering dominates at high doping concentrations.

Combined scattering mechanisms yield excellent agreement with experiments.

Abstract

The mechanisms causing the reduction in lattice thermal conductivity in highly P- and B-doped Si are looked into in detail. Scattering rates of phonons by point defects, as well as by electrons, are calculated from first principles. Lattice thermal conductivities are calculated considering these scattering mechanisms both individually and together. It is found that at low carrier concentrations and temperatures phonon scattering by electrons is dominant and can reproduce the experimental thermal conductivity reduction. However, at higher doping concentrations the scattering rates of phonons by point defects dominate the ones by electrons except for the lowest phonon frequencies. Consequently, phonon scattering by point defects contributes substantially to the thermal conductivity reduction in Si at defect concentrations above $10^{19}$ cm$^{-3}$ even at room temperature. Only when, phonon scattering by both point defects and electrons are taken into account, excellent agreement is obtained with the experimental values at all temperatures.