Monolayer MoS2 Optoelectronic Synapses on Fe:LiNbO3 Substrate with Photovoltaic Control for Neuromorphic Applications.

Two-dimensional (2D) materials, with excellent optoelectronic properties and ultrathin structural features, have emerged as promising candidates for constructing optoelectronic synapse devices (OSDs). However, these 2D OSDs rely on van der Waals heterostructures formed by stacking multiple 2D materials or hybrid stacks of 2D and organic materials, a process that significantly complicates device fabrication. In this work, we simplify the structure of 2D OSDs to a monolayer molybdenum disulfide (MoS2) with a Fe:LiNbO3 crystal as the substrate. A monolayer MoS2 was transferred onto the surface of Fe:LiNbO3 with a pair of electrodes. Under the illumination of a 632.8 nm optical signal, a spatial electric field distribution was generated on the Fe:LiNbO3 surface due to the photovoltaic effect, which modulates the band structure of MoS2, thereby realizing the optical signal perception and storage. This MoS2/Fe:LiNbO3 structure exhibits remarkable optical synapse-like properties, including both long-term and short-term synaptic plasticity, with a paired-pulse facilitation index of 1.32. Based on this, the flicker fusion visual characteristics in biology were simulated, and the critical fusion frequency was measured to be 0.5 mHz. The result indicates the device has advantages in perceiving low-frequency signals below 0.5 mHz in multifrequency environments. Meanwhile, the MoS2/Fe:LiNbO3 structure, serving as a visual neural synapse, exhibited excellent noise filtering ability for input signals. After a noisy data set was processed by the device for 1546 s, the accuracy of image recognition training increased significantly from the original 88.7% to 99.5%. This work simplifies the structure of 2D OSDs, benefiting the construction of visual optoelectronic synapse devices.