Recent studies reveal that four-phonon scattering is generally important in determining thermal conductivities of solids. However, these studies have been focused on materials where thermal conductivity $kappa$ is dominated by acoustic phonons, and the impact of four phonon scattering, although significant, is still generally smaller than three-phonon scattering. In this work, taking AlSb as example, we demonstrated that four-phonon scattering is even more critical to three-phonon scattering as it diminishes optical phonon thermal transport, and therefore significantly reduces the thermal conductivities of materials in which optical branches have long three-phonon lifetimes. Also, our calculations show that four-phonon scattering can play an extremely important role in weakening the isotope effect on $kappa$. Specifically, four-phonon scattering reduces the room-temperature $kappa$ of the isotopically pure and natural-occurring AlSb by 70$%$ and 50$%$, respectively. The reduction for isotopically pure and natural-occurring c-GaN is about 34$%$ and 27$%$, respectively. For isotopically-pure w-GaN, the reduction is about 13$%$ at room temperature and 25$%$ at 400 K. These results provided important guidance for experimentalists for achieving high thermal conductivities in III-V compounds for applications in semiconductor industry.
Download