First-principles prediction of two-dimensional Janus XMInZ[formula omitted](X [formula omitted] Cl, Br, I; M [formula omitted] Mg, Ca; and Z [formula omitted] S, Se, and Te) with promising spintronic and photocatalytic properties

Abstract

Janus two-dimensional (2D) materials with asymmetric structures and intrinsic dipole moments have recently drawn enormous attention due to their appealing performance in diverse fields of nanoelectronics, optoelectronics, spintronics, and photocatalytic water splitting. In this paper, we propose a novel 2D Janus family named XMInZ2(X = Cl, Br, I; M = Mg, Ca; and Z = S, Se, and Te) and investigate their properties employing first-principles calculations. Using phonon dispersion, seventeen compounds of the predicted XMInZ2 monolayers are proved to be dynamically stable. The electronic band structures reveal that all stable XMInZ2 monolayers are direct bandgap semiconductors among which XMgInZ2 have larger bandgaps than XCaInZ2 monolayers. Lack of mirror symmetry gives rise to distinct Rashba spin-splitting (RSS) at Γ point of conduction bands in most XMInZ2 monolayers and the largest Rashba coefficient (αRΓC= 1.112 eVÅ) belongs to BrCaInTe2. Furthermore, comparing the projected band structures with and without the spin–orbit coupling (SOC) effect, it is found that the inclusion of SOC leads to band inversion between the lower conduction band (LCB) and upper valence band (UVB) of ICaInS2 monolayer. In terms of photocatalytic properties, some Janus XMInZ2 monolayers possess appropriate band edge positions for overall water splitting owing to their intrinsic dipole moments. Particularly, BrMgInTe2, BrCaInTe2, and ICaInTe2 due to their smaller bandgaps, larger solar light absorptions, and efficient separation and transport of electrons and holes are superior photocatalysts for water splitting. These explorations can pave the way for the design of highly efficient spintronic and photocatalytic devices.