Synergistically Engineered All Van der Waals GaS–WSe2 Photodiodes: Approaching Near-Unity Polychromatic Linearity for Multifunctional Optoelectronics

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–WSe₂ 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 10⁵ 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–WSe₂ 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.