Electronic and Excitonic Properties of MSi₂Z₄ Monolayers

Abstract

MA2Z4 monolayers form a new class of hexagonal non‐centrosymmetric materials hosting extraordinary spin‐valley physics. While only two compounds (MoSi2N4 and WSi2N4) are recently synthesized, theory predicts interesting (opto)electronic properties of a whole new family of such two‐dimensional (2D) materials. Here, the chemical trends of band gaps and spin‐orbit splittings of bands in selected MSi2Z4 (M = Mo, W; Z = N, P, As, Sb) compounds are studied from first‐principles. Effective Bethe–Salpeter‐equation‐based calculations reveal high exciton binding energies. Evolution of excitonic energies under external magnetic field is predicted by providing their effective g‐factors and diamagnetic coefficients, which can be directly compared to experimental values. In particular, large positive g‐factors are predicted for excitons involving higher conduction bands. In view of these predictions, MSi2Z4 monolayers yield a new platform to study excitons and are attractive for optoelectronic devices, also in the form of heterostructures. In addition, a spin‐orbit induced bands inversion is observed in the heaviest studied compound, WSi2Sb4, a hallmark of its topological nature.

Exploration of the Two-Dimensional Ising Magnetic Materials in the Triangular Prismatic Crystal Field

“…These materials show semiconductor characteristics and are notable for their excellent electronic properties as well as their robust environmental stability. Building on this achievement, there has been heightened research interest in the MX 2 Y 4 family of layered materials. , Noteworthy research includes the discovery of unique electronic effects in CrSi 2 Y 4 (Y = N, P), the electronic and excitonic properties in MSi 2 Y 4 (M = Mo, W; Y = N, P, As, Sb) films, the exploration of new stable Janus MX 2 Y 4 (M = Sc ∼ Zn, Y ∼ Ag, Hf ∼ Au; X = Si, Ge; Y = N, P) monolayers for potential applications, the investigation of the electronic structure of MX 2 Y 4 (M = Ti, Cr, Mo; X = Si; Y = N, P) bilayers under vertical strain, an approach to construct MX 2 Y 4 family monolayers with a septuple-atomic-layer structure, and the prediction of an indirect band gap semiconductor Janus MSiGeN 4 (M = Mo, W) monolayers …”

Tunable structural phases and electronic properties of group V MSi2N4 (M = V, Nb, Ta) nanosheets via surface hydrogenation: a first-principles study

“…4–7 Versatile electronic and magnetic properties have emerged in these MA 2 Z 4 systems, which are significantly dependent on the metal component and structural phase. 3,4 For the group-VI MSi 2 Z 4 (M = Mo, W; Z = P, As) ones, their H-phase structures are direct-gap semiconductors, 8,9 which possess outstanding mechanical, dynamical, electronic, and piezoelectric properties. 10 However, their T-phase structures are dynamically unstable and will transform into a distorted T d -phase conformation via metal dimerization.…”

Modulating the electronic properties and band alignments of the arsenene/MoSi2N4 van der Waals heterostructure via applying strain and electric field

“…10 The MoSi 2 N 4 monolayer possesses hexagonal lattice structure and an indirect bandgap of about 1.79 eV. 11,12 The MA 2 Z 4 monolayers and Janus counterparts are regarded as promising candidates for valleytronics, 13–17 and their valley-contrasting properties can be significantly improved using various ferromagnetic substrates via the proximity effect. 18,19 Recent theoretical studies predicate that the MoSi 2 N 4 monolayer can serve as a photocatalyst for water splitting.…”