Electric field effect on the thermal conductivity of wurtzite GaN

TL;DR

This study uses first-principles calculations to explore how strong electric fields influence the thermal conductivity of wurtzite GaN, revealing significant directional dependence due to bond and symmetry changes.

Contribution

It provides new insights into the impact of high electric fields on phonon transport and thermal conductivity in GaN, a key material for power electronics.

Findings

Electric fields alter thermal conductivity via bond stiffness and ionicity.

Out-of-plane electric fields increase or decrease thermal conductivity depending on direction.

In-plane electric fields significantly decrease thermal conductivity due to symmetry breaking.

Abstract

Gallium nitride (GaN), a wide band-gap semiconductor, has been broadly used in power electronic devices due to its high electron mobility and high breakdown voltage. Its relatively high thermal conductivity makes GaN a favorable material for such applications, where heat dissipation is a major concern for device efficiency and long-term stability. However, in GaN-based transistors, where the active region can withstand extremely strong electric fields, the field effect on the thermal transport properties has drawn little attention so far. In this work, we apply first-principles methods to investigate phonon properties of wurtzite GaN in the presence of a near-breakdown electric field applied along different crystallographic directions. We find that the electric field changes thermal conductivity considerably via impacting the bond stiffness and ionicity as well as the crystal symmetry, although it has little effect on phonon dispersions. The presence of an out-of-plane electric field increases (decreases) the thermal conductivity parallel (perpendicular) to the electric field, which is attributed to different changes of the Ga-N bond stiffness and ionicity. When an in-plane electric field is applied, the sizable decrease of thermal conductivities along all directions is attributed to the crystal symmetry breaking that enhances the phonon-phonon scattering. Our study provides insights into the effect of extreme external electric fields on phonon transport properties in wide-gap semiconductors.