Ab Initio Discovery of Group IV–V Monolayers with Superlative Mechanical, Electronic, and Transport Properties

Much effort has been made to discover new two-dimensional semiconductors with exotic properties for exciting applications. Herein, we predict a class of group IV–V monolayers by first-principles calculations with chemical stoichiometry α′-M^IVX^V (M = C, Si, Ge, Sn, Pb; X = N, P, As, Sb, Bi), which consist of four sublayers in the M-X-X-M rather than the earlier extensively reported X-M-M-X stacking sequence. Among these 25 allotropes, we identify that 19 combinations hold great possibility to be realized in experiments by securing their robust bonding, energetic, dynamical, thermal, and mechanical stabilities. Electronic band structures reveal that except for 3 metallic materials verified by the HSE06 hybrid functional in the presence of the spin–orbit coupling (SOC) effect, the remaining 16 monolayers are intrinsic semiconductors due to the absence of surface dangling bonds, whose direct or indirect bandgaps range from 0.01 to 1.23 eV at the PBE + SOC level. Also, it is found that all of these semiconductors exhibit a pair of inequivalent K valleys in the conduction and valence bands. The strong SOC effect in semiconductors made up of heavy elements leads to the remarkable valley spin splitting in the absence of inversion symmetry. The robust spin-valley locking can not only realize the coexistence of spin and valley Hall effects but also achieve fascinating valley polarization by the irradiation of circularly polarized infrared light. The ultrahigh ultimate tensile strengths endow these semiconducting systems with superior tailored properties. Their considerable and anisotropic mobilities facilitate fast carrier transportation and exciton separation efficiency. Overall, these appealing properties along with viable synthesizability will provide semiconducting α′-M^IVX^V monolayers with tremendous opportunities in a broad variety of potential applications.