Tunable Ultrafast Nonlinear Optical Properties of Graphene/MoS₂ van der Waals Heterostructures and Their Application...

For van der Waals (vdW) heterostructures, optical and electrical properties ( e.g., saturable absorption and carrier dynamics) are strongly modulated by interlayer coupling, which may be due to effective charge transfer and band structure recombination. General theoretical studies have shown that the complementary properties of graphene and MoS₂ enable the graphene/MoS₂ (G/MoS₂) heterostructure to be used as an important building block for various optoelectronic devices. Here, density functional theory was used to calculate the work function values of G/MoS₂ with different thicknesses of MoS₂, and its relaxation dynamic mechanism was illustrated. The results reveal that the G/MoS₂ heterostructure interlayer coupling can be tuned by changing the thickness of MoS₂, furthering the understanding of the fundamental charge-transfer mechanism in few-layer G/MoS₂ heterostructures. The tunable carrier dynamics and saturable absorption were investigated by pump-probe spectroscopy and open-aperture Z-scan technique, respectively. In the experiments, we compared the performances of Q-switched lasers based on G/MoS₂ heterostructures with different MoS₂ layers. Taking advantage of ultrafast recovery time and good saturable absorption properties, a femtosecond solid-state laser at 1.0 μm with G/MoS₂ heterostructure saturable absorber was successfully achieved. This study on interlayer coupling in G/MoS₂ may allow various vdW heterostructures with controllable stacking to be fabricated and shows the promising applications of vdW heterostructures for ultrafast photonic devices.