First-principles study of thermal transport properties in the two- and three-dimensional forms of Bi₂O₂Se

Recently, an air-stable layered semiconductor Bi₂O₂Se has been synthesized [Nat. Nanotechnol., 2017, 12, 530; Nano Lett. 2017, 17, 3021]. It possesses ultrahigh mobility, semiconductor properties, excellent environmental stability and easy accessibility. Here, we report on the thermal transport properties in monolayer (ML), bilayer (BL), and bulk forms of Bi₂O₂Se using density-functional theory and the Boltzmann transport approach. The results show that the ML exhibits better thermal transport properties than the BL and bulk. The intralayer opposite phonon vibrations greatly suppress the thermal transport and lead to an ultralow lattice thermal conductivity of ∼0.74 W m^-1 K^-1 in the ML, which has a large band gap of ∼2.12 eV, a low value of average acoustic group velocity of ∼0.76 km s^-1, low-lying optical modes of ∼0.54 THz, strong optical-acoustic phonon coupling, and large Grüneisen parameters of ∼5.69. The size effect for all three forms is much less sensitive due to their short intrinsic phonon mean free path (MFP).