Characterization of Lattice Thermal Transport in Two-Dimensional BAs, BP, and BSb: A First-Principles Study

Recently, bulk BAs has been confirmed experimentally to have a room temperature thermal conductivity of around 1,100 W/m-K. However, the monolayer hexagonal form of boron arsenide (h-BAs) has seldom been studied. Here, we use a first-principles approach and solve the Boltzmann Transport Equation for phonons to obtain a surprisingly high thermal conductivity in this material. We determine h-BAs to have a much lower Debye temperature and average phonon group velocity compared to the other monolayer boron-V compounds of boron nitride (h-BN) and boron phosphide (h-BP), yet curiously it possesses a higher thermal conductivity. Further investigation reveals that this is due to the large phonon frequency gap caused by large mass imbalances, where there is a restricted Umklapp phonon-phonon scattering channel and consequently results in a higher thermal conductivity. We determine the intrinsic lattice thermal conductivity of monolayer BAs to be 362.62 W/m-K at room temperature, which is considerably higher compared to the other monolayer boron-V compounds of h-BN (231.96 W/m-K), h-BP (187.11 W/m-K), and h-BSb (87.15 W/m-K). This study opens the door for investigation into a new class of monolayer structures and the properties they possess.