High mobility and excellent thermoelectric performance monolayer ZnX₂Z₄ (X = In, Al, Ga; Z = S, Se, Te) materials

Recently, two-dimensional (2D) layered polarized ZnIn2S4 nanosheets have been successfully synthesized in experiments. However, the polarized monolayers are unstable in air, which hinders their practical applications. Therefore, in this work, we proposed a new family of nonpolarized monolayers (β2-phase) ZnX2Z4 (X = In, Al, and Ga; Z = S, Se, and Te) by first-principles. It is confirmed that the energies of β2-phase ZnX2Z4 are lower than those of the polarized and β-phase ZnX2Z4 monolayers. Moreover, these ZnX2Z4 monolayers have not only desirable indirect band gaps but also high electron mobility (up to 103 cm2 V-1 s-1), revealing a fascinating visible light absorption range. Furthermore, β2-phase ZnX2Te4 (X = In, Al, and Ga) has ultra-low lattice thermal conductivity and high ZT value (up to 0.89), suggesting that these monolayers can be good candidates for thermoelectric materials. These new 2D ternary monolayers not only effectively broaden the family of 2D materials but also provide promising candidates for optoelectronic and thermoelectric materials.