Enhanced Infrared Second-Harmonic Generation and Shift Current in As/SnS ₂ van der Waals Heterostructure via Symmetry Engineering

The development of high-performance second-order nonlinear optical (NLO) materials is pivotal for advancing integrated photonic and on-chip optoelectronic devices. However, the practical implementation of two-dimensional (2D) materials in such devices is hindered by their limited infrared response and inherent centrosymmetry in some specific structures, which forbid second-order NLO processes. Herein, we construct a van der Waals heterostructure by stacking centrosymmetric monolayers As and SnS₂ to break the space inversion symmetry. This heterostructure exhibits a pronounced second-harmonic generation (SHG) response in the infrared regime, which is attributed to the modulation of the linear response by electronic intraband motion. Simultaneously, the heterostructure shows a strong second-order shift current response, surpassing that of some conventional ferroelectric materials, making it a promising candidate for detector and solar cell applications. Furthermore, we reveal that the equi-biaxial strain effectively modulates the electronic band structure, which in turn provides an important method to spectrally regulate the SHG and shift current response bands. This work not only validates heterostructure construction as a highly effective approach for expanding the selection of NLO materials but also deepens the understanding of the second-order NLO responses.