Complementary Photoresponse in van der Waals Heterostructures for Insect-Inspired Neuromorphic Vision

Complementary responses to identical stimuli, essential to biological sensory processing, are rarely realized in solid-state systems. Here, we report such behavior in the van der Waals (vdW) complex-anion thiophosphate LiInP₂Se₆, where two specimens with distinct defect landscapes exhibit opposing photoconductive responses under identical illumination when integrated as top-gate dielectrics in monolayer MoS₂ field-effect transistors (FETs). These contrasting behaviors are supported by density functional theory, photoluminescence spectroscopy, and electrical measurements. Leveraging this intrinsic contrast, we construct a low-power and miniaturized photonic circuit that converts looming light stimuli into electrical spikes, where spike timing encodes the velocity of the approaching object. The response profile emulates the dynamics of lobula giant movement detector (LGMD) neurons in insects, positioning complex anion 2D thiophosphates as a compelling platform for neuromorphic vision.