High‐Performance Self Powered Broadband Photodetection in Graphene‐Contacted MoTe ₂ /WS ₂ van der Waals Heterostructures via Interfacial Band Engineering

Van der Waals (vdW) heterostructures composed of 2D materials offer a versatile platform for next-generation optoelectronic devices due to their tunable band structures, strong light matter interactions, and clean vdW interfaces. Here, this work reports on the fabrication and in depth characterization of a broadband photodetector based on a vertically stacked MoTe₂/WS₂ heterostructure with a few layer graphene serving as transparent, tunable contact electrodes. The device is assembled entirely through mechanical exfoliation and dry transfer, ensuring pristine interfaces and preserving the intrinsic properties of the materials. Systematic optical, electrical, and density functional theory (DFT) analysis reveal a type II band alignment at the MoTe₂ WS₂ interface, facilitating efficient photocarrier separation. The incorporation of graphene contacts significantly enhances rectification behavior over 10⁵, suppresses contact induced recombination and improves photocurrent response due to their tunable work function and van der Waals bonding. The device exhibits a broadband photoresponse (220-850 nm), high responsivity (≈650 A W^-1), large detectivity (≈1.3 × 10¹² Jones), and external quantum efficiency (≈3.5 × 10⁵ %). Time resolved studies demonstrate rapid, bias dependent photoresponse, making the device suitable for high speed photodetection. This study highlights the critical role of contact engineering and interfacial band alignment in optimizing 2D heterostructure based optoelectronics.