Nonlinear Optical and Photocurrent Responses in Janus MoSSe Monolayer and MoS2-MoSSe van der Waals Heterostructure br

Two-dimensional (2D) transition metal dichalcogenidesare promising materials platforms for a variety of optoelectronic deviceapplications. Janus 2D materials are a rising class of 2D materials withlow symmetry, which leads to the emergence of out-of-plane electricpolarization and piezoelectricity. Usingfirst-principles density func-tional theory, we show that monolayer and bilayer heterostructureJanus MoSSe moieties exhibit strong nonlinear optical responses thatare vanishing in the non-Janus form. The absence of horizontal mirrorplane symmetry enables a circular photocurrent as well as a large out-of-plane second harmonic generation (SHG) and shift photocurrent.Through a comparative study of the Janus heterostructure MoS2-MoSSe onfive distinct stacking configurations, wefind that themagnitude of the out-of-plane SHG in the Janus heterostructure isenhanced due to the interlayer coupling and interference effect compared to that of monolayer MoSSe. Thus, Janus 2D materialsoffer a unique opportunity for exploring nonlinear optical phenomena and designing configurable layered nonlinear optical materials