Effects of nano-void density, size, and spatial population on thermal conductivity: a case study of GaN crystal

TL;DR

This study combines analytical modeling and large-scale molecular dynamics simulations to understand how nanoscale void defects affect the thermal conductivity of GaN crystals, providing insights for phonon engineering.

Contribution

It introduces a new analytical expression linking defect characteristics to thermal conductivity, validated through simulations and experiments.

Findings

Thermal conductivity decreases with increased void density.

Void size and spatial distribution significantly influence thermal transport.

The model accurately predicts experimental measurements.

Abstract

The thermal conductivity of a crystal is sensitive to the presence of surfaces and nanoscale defects. While this opens tremendous opportunities to tailor thermal conductivity, a true "phonon engineering" of nanocrystals for a specific electronic or thermoelectric application can only be achieved when the dependence of thermal conductivity on the defect density, size, and spatial population is understood and quantified. Unfortunately, experimental studies of effects of nanoscale defects are quite challenging. While molecular dynamics simulations are effective in calculating thermal conductivity, the defect density range that can be explored with feasible computing resources is unrealistically high. As a result, previous work has not generated a fully detailed understanding of the dependence of thermal conductivity on nanoscale defects. Using GaN as an example, we have combined physically-motivated analytical model and highly-converged large scale molecular dynamics simulations to study effects of defects on thermal conductivity. An analytical expression for thermal conductivity as a function of void density, size, and population has been derived and corroborated with the model, simulations, and experiments.