Stacking-dependent nonlinear optical properties of MoS ₂ /WS ₂ van der Waals heterostructures: an ab initio study

Abstract The different stacked heterostructures of transition metal dichalcogenides, which are the building blocks of moiré structures, represent a novel class of two-dimensional (2D) materials with promising applications in advanced optoelectronics and nonlinear photonics, while also providing a platform for fundamental studies of 2D semiconductor physics. In this work, we systematically investigate the linear and nonlinear optical (NLO) responses, as well as the linear electro-optical (LEO) properties, of MoS ₂ /WS ₂ heterostructures with varying stack alignments using first-principles density functional theory and quasiparticle approximations. We observe a change in bandgap character between scalar and fully relativistic electronic band structures, which is preserved in both relativistic and quasiparticle band structures. We used quasiparticle band gaps and a scissors-correction method to calculate the second-harmonic generation (SHG) susceptibilities of these stackings. Our results show that the calculated SHG spectra of different stacking configurations are larger (in order of 10 {}³ pm V ⁻¹ ) in the visible-near-IR range, which is very high compared to the well-known commercial NLO materials, making these atomically thin stackings can be easily integrated with photonics and flexible electronics. The calculated LEO coefficients remain superior at ∼−3.5 pm V ⁻¹ in the low photon energy range and are significantly higher compared to those reported for the common semiconductors. These enhanced properties suggest the potential benefits of these van der Waals heterostructure stackings in nonlinear applications and demonstrate the amenability of MoS ₂ /WS ₂ heterostructure stacking configurations to spectroscopic investigation.