Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics – a Comparative Study with Gallium Nitride

Abstract

Abstract Wurtzite Zinc-Oxide ( w -ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w -ZnO. In this paper, we determine the thermal conductivity of w -ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride ( w -GaN) – another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w -ZnO. However, the thermal conductivity values show large differences (400 W/mK of w -GaN vs. 50 W/mK of w -ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w -GaN, w -ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering and the weaker interatomic bonds in w -ZnO leads to smaller phonon group velocities. The thermal conductivity of w -ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w -ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w -ZnO-based electronics.