  Tin chalcogenides (SnS, SnSe, and SnTe) are found to have improved
thermoelectric properties upon the reduction of their dimensionality. Here we
found the tilted AA + s stacked two-dimensional (2D) SnTe bilayer as the most
stable phase among several stackings as predicted by the structural
optimization and phonon transport properties. The carrier mobility and
relaxation time are evaluated using the deformation potential theory, which is
found to be relatively high due to the high 2D elastic modulus, low deformation
potential constant, and moderate effective masses. The SnTe bilayer shows a
high Seebeck coefficient, high electrical conductivity, and ultralow lattice
thermal conductivity. High TE figure of merit (ZT) values, as high as 4.61
along the zigzag direction, are predicted for the SnTe bilayer. These ZT values
are much enhanced as compared to the bulk as well as monolayer SnTe and other
2D compounds.
