Optoelectronic synapse based on a BiI3/Bi2Se3 van der Waals heterostructure for neuromorphic visions

In this paper, we demonstrate a fully optical neuromorphic vision sensor based on a BiI3/Bi2Se3 van der Waals heterostructure grown by sequential vapor deposition. High-quality vdW epitaxy produces strongly c axis-oriented BiI3 on Bi2Se3, forming a type-I band alignment and interfacial charge accumulation layer. This architecture suppresses dark current by one order of magnitude compared with pristine Bi2Se3 while generating intense persistent photoconductivity across visible-to-near-infrared wavelengths, an intrinsic, gate-free nonvolatile memory effect that directly enables synaptic plasticity. Using only optical pulses, a single two-terminal device faithfully emulates paired-pulse facilitation, short- to long-term plasticity transition, wavelength- and timing-dependent axon-multi-synapse integration, and frequency-dependent image memorization with controllable forgetting. These results establish the BiI3/Bi2Se3 heterostructure as a promising platform for broadband neuromorphic vision.