An on-Si directional second harmonic generation amplifier for MoS₂/WS₂ heterostructure

Transition metal dichalcogenides (TMD) heterostructure is widely applied for second harmonic generation (SHG) and holds great promises for laser source, nonlinear switch, and optical logic gate. However, for atomically thin TMD heterostructures, low SHG conversion efficiency would occur due to reduction of light–matter interaction length and lack of phase matching. Herein, we demonstrated a facile directional SHG amplifier formed by MoS₂/WS₂ monolayer heterostructures suspended on a holey SiO₂/Si substrate. The SHG enhancement factor reaches more than two orders of magnitude in a wide spectral range from 355 to 470 nm, and the radiation angle is reduced from 38° to 19° indicating higher coherence and better emission directionality. The giant SHG enhancement and directional emission are attributed to the great excitation and emission field concentration induced by a self-formed vertical Fabry–Pérot microcavity. Our discovery gives helpful insights for the development of two-dimensional (2D) nonlinear optical devices.