Ab initio study of the unusual thermal transport properties of boron arsenide and related materials

Recently, using a first principles approach, we predicted that zinc blende boron arsenide (BAs) will have an ultrahigh lattice thermal conductivity, κ, of over 2000 Wm^-1K^-1 at room temperature (RT), comparable to that of diamond. Here, we provide a detailed ab initio examination of phonon thermal transport in boron arsenide, contrasting its unconventional behavior with that of other related materials, including the zinc blende crystals boron nitride (BN), boron phosphide, boron antimonide, and gallium nitride (GaN). The unusual vibrational properties of BAs contribute to its weak phonon-phonon scattering and phonon-isotope scattering, which are responsible for its exceptionally high κ. The thermal conductivity of BAs has contributions from phonons with anomalously large mean free paths (∼2 μm), two to three times those of diamond and BN. This makes κ in BAs sensitive to phonon scattering from crystal boundaries. An order of magnitude smaller RT thermal conductivity in a similar material, zinc blende GaN, is connected to more separated acoustic phonon branches, larger anharmonic force constants, and a large isotope mixture on the heavy rather than the light constituent atom. The striking difference in κ for BAs and GaN demonstrates the importance of using a microscopic first principles thermal transport approach for calculating κ. BAs also has an advantageous RT coefficient of thermal expansion, which, combined with the high κ value, suggests that it is a promising material for use in thermal management applications.