Electric field effect on the thermal conductivity of wurtzite GaN

Abstract

Gallium nitride (GaN), a wide bandgap 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, ionicity, anharmonicity, and 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 in the Ga–N bond stiffness and ionicity and the scattering rates of phonons traveling along different directions. When an in-plane electric field is applied, the sizable decrease in thermal conductivities along all directions is attributed to the crystal symmetry breaking that enhances the phonon–phonon scattering. Our study provides insight into the effect of extreme external electric fields on phonon transport properties in wide-gap semiconductors.