Synaptic Behavior in SnSe2 Field-Effect Transistors Induced by Surface Oxide and Trap Dynamics

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 (SnSe2) 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 SnSe2 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 SnSe2 as a robust platform for optoelectronic neuromorphic devices. By exploiting interfacial trap states and gate control, SnSe2-based transistors emulate essential synaptic functionalities with excellent stability, offering new opportunities for 2D-material-enabled scalable neuromorphic hardware.