Electrostatic Interaction Determines Thermal Conductivity Anisotropy of Bi 2O 2Se: A Comparison With Bi 2Se 3

Air-stable layered semiconductor Bi2O2Se has attracted extensive interest recently for applications in electronics, optoelectronics, ferroelectrics, and thermoelectrics. For many of these applications, thermal transport in Bi2O2Se is of great importance but the understanding remains elusive. Here, we perform a combined experimental and theoretical study on the anisotropic thermal conductivity of single-crystalline Bi2O2Se in comparison with its parent compound Bi2Se3 over the temperature range of 80-300 K using the time-domain thermoreflectance measurements and ab initio phonon Boltzmann transport calculations. Compared with Bi2Se3, Bi2O2Se exhibits relatively higher thermal conductivity along the through-plane direction but it is lower along the in-plane direction, resulting in substantially smaller thermal anisotropy. We find the smaller thermal anisotropy of Bi2O2Se mainly originates from its stronger interlayer electrostatic interaction compared to the typical van der Waals coupling in layered materials, which makes the phonon isoenergy surfaces less anisotropic and thus weakens phonon focusing along the in-plane directions. Our study advances the fundamental understanding of thermal anisotropy in layered materials with various interlayer interactions and will facilitate the applications of Bi2O2Se in electronics and thermoelectrics.