Phonon transport properties of bulk and monolayer GaN from first-principles calculations

The thermal conductivity of isotopically pure wurtzite GaN and the corresponding two-dimensional monolayer crystals are investigated based on first-principles calculations and phonon Boltzmann transport equation. It is found that the c-axis thermal conductivity of defect-free wurtzite GaN is 42-11% higher than that along the in-plane direction when temperature increases from 100 to 800 K. Our calculation also shows that the thermal conductivity of monolayer GaN with hexagonal lattice is higher than that with haeckelite lattice by a factor of four at room temperature. The phonon dispersion relation, phonon group velocity and the phonon scattering rate are extracted to uncover the underlying physical mechanism. The thermal conductivity accumulation function with respect to the phonon mean free path and the relative contribution of each phonon branch for the two kinds of monolayer GaN are further calculated as compared to that of graphene. These investigations would provide important guidance to develop GaN-based electronic and photonic device. (C) 2017 Elsevier B. V. All rights reserved.