Spectral concentration of thermal conductivity in GaN—A first-principles study

Abstract

We find using first-principles analysis of thermal conductivity (k) in isotopically pure Gallium nitride (GaN) that almost 60% of the heat is conducted by phonons in a very narrow frequency range of 5-7 THz (spanning only 9% of the frequencies in GaN). This spectral focusing of thermal conductivity is found to be due to a combination of two effects - a large increase in lifetimes of phonons through suppression of anharmonic scattering in the 5-7 THz frequency range coupled with a large phonon density of states at the same frequencies. Understanding of the effect is provided by solving the phonon Boltzmann transport equation in the single mode relaxation time approximation along with the use of harmonic and anharmonic force constants derived from density functional theory. The results can have important implications for engineering the thermal performance of devices based on GaN. ©2018 Author(s).