Orbitally driven low thermal conductivity of monolayer gallium nitride (GaN) with planar honeycomb structure: a comparative study

Monolayer gallium nitride (ML GaN) with honeycomb structure was successfully fabricated recently in experiments, generating enormous research interest for its promising applications in nano- and opto-electronics. By solving the Boltzmann transport equation (BTE) based on first-principles calculations, we performed a comprehensive study of the phonon transport properties of ML GaN, with detailed comparison to bulk GaN, 2D graphene, silicene and ML BN with similar honeycomb structure. We find that the thermal conductivity (κ) of ML GaN (14.93 W/mK) is more than two orders of magnitude lower than that of graphene and is even lower than that of silicene with a buckled structure. Systematic analysis is performed based on the study of the contribution from phonon branches, comparison among the phonon mode levels and phonon anharmonicity. Further deep insight is gained from the electronic structure. Resulting from the special sp orbital hybridization mediated by the Ga-d orbital in ML GaN, the strongly polarized Ga–N bond and its inhomogeneous distribution could lead to the intrinsic low κ of ML GaN. The unraveled orbitally driven low κ of ML GaN offers fundamental understanding of phonon transport and will shed light on further studies of phonon transport in 2D materials .