Synergistically Engineered All Van der Waals GaS–WSe ₂ Photodiodes: Approaching Near‐Unity Polychromatic Linearity for Multifunctional Optoelectronics

Abstract Van der Waals (vdW) heterojunctions represent a significant frontier in post‐Moore era optoelectronics, especially in optimizing photosensor performance through multivariate approaches. Here synergistic engineering of GaS–WSe ₂ all‐vdW photodiodes is investigated, which exhibit broadband detection (275–1064 nm), multispectral unity approaching linearity, alongside a substantial linear dynamic range (LDR) of 106.78 dB. Additionally, the photodiodes achieve a remarkable on/off ratio of 10 ⁵ and rapid response edges of 545/471 µs under a 405 nm pulsed source, exhibiting ultralow light detection capabilities (dark currents ∼fA), culminating in a peak responsivity of 376.78 mA W ⁻¹ and a detectivity of 4.12 × 10¹¹ Jones under 450 nm illumination, complemented by an external quantum efficiency (EQE) of 30% and a fill factor of ≈0.33. Based on the analysis of multiple all‐vdW devices, the importance of Fermi‐level pinning free metal–2D interface engineering that enables effective modulation of the Schottky barrier height via vdW metal contacts is highlighted and meticulous thickness‐engineered layers in developing a robust depletion region within the type‐II GaS–WSe ₂ heterojunction are employed, ultimately achieving a favorable balance among photocarrier generation recombination, separation, transport, and extraction. This comprehensive investigation sets the stage for future developments in critically engineered next‐generation vdW optoelectronic devices.