  Monolayer semiconductors of group-VA elements (As, Sb, Bi) with graphenelike
buckled structure offer a potential to achieve nanoscale electronic,
optoelectronic and thermoelectric devices. Motivated by recently-fabricated Sb
monolayer, we systematically investigate the thermoelectric properties of
$\beta$-As, Sb and Bi monolayers by combining the first-principles calculations
and semiclassical Boltzmann transport theory. The generalized gradient
approximation (GGA) plus spin-orbit coupling (SOC) is adopted for the electron
part, and GGA is employed for the phonon part. It is found that SOC has
important influences on their electronic structures, especially for Bi
monolayer, which can induce observable SOC effects on electronic transport
coefficients. More specifically, SOC not only has detrimental influences on
electronic transport coefficients, but also produces enhanced effects. The
calculated lattice thermal conductivity decreases gradually from As to Bi
monolayer, and the corresponding room-temperature sheet thermal conductance is
161.10 $\mathrm{W K^{-1}}$, 46.62 $\mathrm{W K^{-1}}$ and 16.02 $\mathrm{W
K^{-1}}$, which can be converted into common lattice thermal conductivity by
dividing by the thickness of 2D material. The sheet thermal conductance of Bi
monolayer is lower than one of other 2D materials, such as semiconducting
transition-metal dichalcogenide monolayers and orthorhombic group IV-VI
monolayers. A series of scattering time is employed to estimate the
thermoelectric figure of merit $ZT$. It is found that the n-type doping has
more excellent thermoelectric properties than p-type doping for As and Bi
monolayer, while the comparative $ZT$ between n- and p-type doping is observed
in Bi monolayer. These results can stimulate further experimental works to open
the new field for thermoelectric devices based on monolayer of group-VA
elements.
