  Phonon transports of group-VA elements (As, Sb, Bi) monolayer semiconductors
have been widely investigated in theory, and Sb monolayer (antimonene) of them
has recently been synthesized. In this work, phonon transport of SbAs monolayer
is investigated from a combination of first-principles calculations and the
linearized phonon Boltzmann equation. It is found that the lattice thermal
conductivity of SbAs monolayer is lower than ones of both As and Sb monolayers,
and the corresponding sheet thermal conductance is 28.8 $\mathrm{W K^{-1}}$ at
room temperature. Calculated results show that group velocities of SbAs
monolayer are between ones of As and Sb onolayers, but phonon lifetimes of SbAs
are smaller than ones of both As and Sb monolayers. Hence, low lattice thermal
conductivity in SbAs monolayer is attributed to very small phonon lifetimes.
Unexpectedly, the ZA branch has very little contribution to the total thermal
conductivity, only 2.4\%, which is obviously different from ones of As and Sb
monolayers with very large contribution. This can be explained by very small
phonon lifetimes for ZA branch of SbAs monolayer. The large charge transfer
from Sb to As atoms leads strongly polarized covalent bond, being different
from As or Sb monolayer. The strongly polarized covalent bond of SbAs monolayer
can induce stronger phonon anharmonicity than As or Sb monolayer, leading to
lower lattice thermal conductivity. It is found that isotope scattering
produces neglectful effect, and the lattice thermal conductivity with the
characteristic length smaller than 30 nm can reach a decrease of about 47\%.
These results may offer perspectives on tuning lattice thermal conductivity by
mixture of multi-elements for applications of thermal management and
thermoelectricity, and motivate further experimental efforts to synthesize
monolayer SbAs.
