Strain-Induced Bandgap Narrowing in Crumpled TMDs for NIR Light Detection

Transition metal dichalcogenides (TMDs) such as MoS₂ and WS₂ emerge as promising materials in optoelectronics, especially for flexible photo- /image-sensors due to their direct bandgap nature. However, the intrinsic bandgaps of these semiconductor monolayers (e.g., MoS₂ ≈1.86 eV and WS₂ ≈2.0 eV) restrict the operational wavelength range of developed photosensors in the visible spectrum. In addition, their ultrathin nature provides a limited optical absorption cross-section that restricts the device's performance. Exploiting the strong impact of strain on the electronic band structure, strain engineering has emerged as a promising approach for adjusting the electrical and optical characteristics of layered semiconductors. In particular, the application of tensile strain in MoS₂ and WS₂ can decrease their bandgaps, which potentially can extend the optical absorption toward the near-infrared (NIR) wavelength. Herein, a non-conventional crumpling approach is employed to incorporate uniaxial tensile strain into a graphene/TMD/graphene metal-semiconductor-metal photodetector (PD) array. The utilized crumpled geometry provides exclusive photon management with enhanced light scattering and trapping at the sinusoidal surface that results in increased light absorption in NIR wavelength range.