Self-Powered Polarized Photodetection and Low-Voltage Modulated Bidirectional Visual Synapse of Ta₂NiS₅/MoS₂/Gr Vertical Heterojunction with Asymmetric Interface Modulation

Modern application scenarios increasingly demand multifunctional integrated photodetectors with high efficiency and low-power consumption. However, existing two-dimensional (2D) heterojunction-based devices face critical challenges. For instance, metal-semiconductor contacts can induce Schottky barriers and Fermi level pinning, which hinder carrier transport and degrade overall performance. To address these issues, this work proposes a vertical van der Waals heterojunction design, employing graphene (Gr) as the top electrode, tantalum nickel sulfide (Ta₂NiS₅) with a narrow-bandgap and anisotropy as the bottom electrodes, and molybdenum disulfide (MoS₂) as the main light-absorbing layer. This architecture engineers reverse built-in electric fields at Ta₂NiS₅/MoS₂ and MoS₂/Gr interfaces and replaces Schottky contacts with ohmic-like transport, leveraging Ta₂NiS₅'s anisotropy and interfacial asymmetry to integrate multiple functions. Under 660 nm light illumination (249.24 mW/cm²), it achieves a high photocurrent density of 171 mA/cm² and an on/off ratio of 3.7 × 10⁴. Under 808 nm light illumination, a self-powered anisotropy ratio of 6.03 is realized. It exhibits excitatory postsynaptic currents (EPSC) under 1064 nm light illumination with an ultralow energy consumption of 82 fJ, alongside bidirectional synaptic weight modulation via bias polarity and light pulse (duration, intensity, and number) control. This integrated design paves the way for advancing multifunctional optoelectronic devices in next-generation integrated systems and artificial intelligence applications.