Enhanced Rashba Effect and Optical Absorption in 2D Janus XMoYZ2 (X = S/Se/Te; Y = Si/Ge; Z = N/P): A First-Principles Study

To overcome the physical constraints during the miniaturization of conventional semiconductor devices, spintronics is playing an increasingly prominent role. The Rashba effect, characterized by spin–momentum locking, has emerged as a promising solution to address challenges. Two-dimensional (2D) Janus transition metal dichalcogenides (TMDCs) break spatial inversion symmetry, creating favorable conditions for the Rashba effect. Based on first-principles calculations, 2D Janus materials XMoYZ2 (X = S/Se/Te; Y = Si/Ge; Z = N/P) were investigated, with strain, external electric field and charge doping employed to modulate the Rashba effect. The strain results reveal that the Rashba constants of XMoYZ2 increase significantly with compressive strain. Specifically, after applying uniaxial strain, the Rashba constant of TeMoSiP2 is enhanced to ~2.2 times its initial value. Compressive strain reduces atomic spacing, enhances orbital overlap, and increases spin–orbit coupling (SOC) strength. All the TeMoYZ2 materials exhibit significant anisotropy under uniaxial strain, which is favorable for spin-oriented transport. SeMoGeP2 shows an almost linear Rashba constant–electric field correlation, while TeMoGeP2 and TeMoSiP2 show non-monotonic variation. The Rashba constant of TeMoSiP2 can be enhanced to ~2.7 times its intrinsic value under either positive or negative applied electric fields. Charge doping induces negligible changes in the SOC effect. Finally, the optical absorption properties of TeMoGeP2, TeMoSiN2, and TeMoSiP2 were investigated. This study clarifies the mechanism underlying the enhancement of Rashba constants in XMoYZ2 materials, enriching the research landscape of spintronics.