Electrostatically enhanced infrared absorption in two-dimensional van der Waals structures.

Two-dimensional (2D) semiconductors exhibit strong light absorption, yet their large bandgaps limit broadband photodetection. While van der Waals (vdW) heterostructures of 2D materials enable infrared excitation through narrowed interlayer bandgaps, achieving efficient control over these interlayer transitions remains a fundamental challenge. Through first-principles simulations and electrostatic engineering approaches, this study establishes a direct correlation between interfacial charge redistribution and enhanced interlayer excitations in 2D vdW structures. The results demonstrate that versatile strategies such as external electric field application, substitutional doping, and graphene interlayer integration effectively reduce interlayer bandgaps by several hundred millielectronvolts while significantly increasing interfacial charge exchange. These engineered heterostructures achieve exceptional absorption coefficients greater than 10⁵ cm^-1 spanning visible to mid-infrared wavelengths. These findings provide essential design principles and offer engineering strategies for developing broadband photodetectors using 2D vdW structures.