Synaptic Behavior in SnSe ₂ Field‐Effect Transistors Induced by Surface Oxide and Trap Dynamics

Abstract 2D semiconductors are attracting considerable interest for neuromorphic electronics for their strong light–matter interaction, defect‐mediated charge dynamics, and suitability for energy‐efficient devices. Among them, tin diselenide (SnSe 2 ) combines Earth abundance, environmental stability, high carrier mobility and persistent photoconductivity that make it a compelling candidate for multifunctional optoelectronic synapses. Here, we investigate multilayer SnSe 2 field‐effect transistors and demonstrate gate‐tunable optoelectronic plasticity. Systematic measurements as a function of temperature, illumination power, and gate bias reveal that the device photoresponse is dominated by trap‐assisted photogating. The interplay between fast and slow recombination channels produces a persistent photocurrent (PPC) that can be finely tuned by the gate voltage. Negative gate bias enhances charge separation and prolongs PPC, enabling long‐term potentiation, while positive gate bias accelerates recombination and suppresses persistence, yielding short‐term memory. Furthermore, short gate voltage pulses enable reversible suppression of persistent photocurrent, allowing controlled switching between short‐ and long‐term memory states. Under repetitive optical stimulation, the devices exhibit cumulative learning and memory retention with high reproducibility. These results highlight SnSe 2 as a robust platform for optoelectronic neuromorphic devices. By exploiting interfacial trap states and gate control, SnSe 2 ‐based transistors emulate essential synaptic functionalities with excellent stability, offering new opportunities for 2D‐material‐enabled scalable neuromorphic hardware.