Wavelength-Dependent Negative/Positive Photoresponse and Infrared Polarization Sensitivity of Two-Dimensional...

Infrared polarization-sensitive visual synapses distinguish target details under background interference or low contrast, serving as the core for meeting critical fields' demand for efficient infrared optical information processing and recognition. Combining negative/positive photoelectric effects overcomes traditional single-polarity photoresponse limitations in simulating biological synapses' excitatory-inhibitory dual states, laying a crucial foundation for encoding complex neural signals and realizing brain-like multi-level information processing. Integrating wavelength-dependent positive/negative photoresponse switching with infrared polarization sensitivity is key to breaking through existing bottlenecks. Herein, we construct a two-dimensional heterojunction using anisotropic narrow-bandgap semiconductor PdSe₂ and semi-metal NbSe₂, successfully fabricating a visual synapse integrating the aforementioned two properties. Under 808/1064 nm light illumination, asymmetric current synaptic pulse modulation is achieved via positive/negative voltage regulation, and positive/negative photoresponse switching is realized under low-voltage modulation. Under 808-2200 nm light illumination, investigations on bias voltage, pulse frequency, and pulse intensity demonstrate that the heterojunction can implement synaptic functions at a low bias of 1 mV, with a single-pulse energy consumption as low as 0.298 pJ. Notably, the heterojunction possesses excellent polarization sensitivity, achieving a polarization ratio of 12.67 under 1550 nm light illumination. This work provides a highly promising platform for the development of high-performance multi-dimensional visual systems.