Achieving Near-Perfect and Broad Light Absorption in Atomically Flat Two-Dimensional Transition Metal Dichalcogenide Heterostructures Through a Simple Resonant Optical Nanocavity

Two-dimensional (2D) atomically thin transition metal dichalcogenide (TMD) monolayers such as MoS₂, MoSe₂, WS₂, and WSe₂, as well as their heterostructures, have attracted significant attention for flexible optoelectronic nanodevice applications. However, in 2D-TMD-based light absorbers for optoelectronic applications, the lower light absorption of thin 2D-TMD monolayers and their heterostructures remains a key limiting factor in device performance. Here, we introduce and describe the design and implementation of a simple resonant optical nanocavity that enables near-perfect light absorption and a wide absorption band within the ultrathin thickness of a 2D-TMD-based heterostructure. The structural design process begins by identifying the properties of the leaky modes required for strong absorption. By performing three-dimensional electromagnetic numerical simulations using a finite difference time domain (FDTD) on the designed 2D-TMD-based heterostructures and investigating their optical properties, we demonstrate near-perfect, broadband absorption within thin 2D-TMDs. In particular, we show that combining the MoS₂ monolayer, MoS₂/WS₂, MoS₂/MoSe₂/MoS₂, and MoS₂/MoSe₂/MoS₂/MoSe₂ heterostructures with SiO₂/Ag nanocavities leads to the highest absorption and a wider absorption spectrum. Specifically, we report near-perfect light absorption, up to 98.08% for a 2 nm thin MoS₂/MoSe₂/MoS₂ heterostructure and 99.02% for a 2.7 nm thin MoS₂/MoSe₂/MoS₂/MoSe₂ heterostructure, by coupling them to strong optical modes in a SiO₂/Ag nanocavity. Our results provide new insights into achieving near-perfect and wide-band absorption, facilitating the design of ultrathin light absorbers for optoelectronic applications such as photodetectors, photovoltaics, and photocatalysts.