Giant enhancement of second-harmonic generation of indium selenide on planar Au

Abstract

Two-dimensional (2D) van der Waals layered γ-type indium selenide (γ-InSe) holds great promise for the development of ultrathin and low-energy-consumption nonlinear optical devices due to its broken inversion symmetry regardless of layer number. Nevertheless, the 2D InSe thin flakes still exhibit short light–matter interaction lengths, thus resulting in low efficiencies of nonlinear optical processes. In this work, we provide a facile 2D semiconductor–metal structure consisting of InSe thin flakes (thickness: 11–54 nm) on planar Au film, which exhibits great second-harmonic generation (SHG) enhancement by a factor of up to 1182. The SHG enhancement is attributed to the interference effect-induced strong electric field in highly absorbing InSe; meanwhile, the increase in reflectivity by Au film also plays an important role. Furthermore, the InSe thickness and excitation wavelength dependences of enhancement factors are revealed. This work provides a convenient approach to developing high-efficiency 2D nonlinear optical devices with ultrathin form.