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

Abstract

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.