Thermally Tunable Fading Memory Enabled by Opto-Ionic-Electronic Coupling in AgInP2S6-Gated Two-Dimensional Field-Effect Transistors.

In conventional field-effect transistors (FETs), the gate dielectric primarily provides electrostatic control of the channel and is engineered to remain chemically and electronically inert to ensure stable operation. Emerging studies, however, suggest that functional dielectrics integrated with two-dimensional (2D) semiconductors can introduce additional physical mechanisms that influence device behavior. Here, we investigate AgInP2S6 (AIPS), a high-κ van der Waals thiophosphate, as a functional top-gate dielectric in MoS2 field-effect transistors. The AIPS/MoS2 heterointerface exhibits coupled opto-ionic-electronic interactions, where defect-mediated sub-bandgap photoactivity and photon-assisted Ag+ ion migration independently occur within the dielectric yet collectively modulate the channel conductance. Optical excitation redistributes charge within the dielectric, gradually reconfiguring the ionic landscape and altering the interfacial electrostatic potential. The resulting conductance exhibits strong temperature dependence. At low temperatures (∼0 °C), reduced phonon activity suppresses Ag+ mobility, leading to persistent photoconductivity. At elevated temperatures (∼80 °C), thermally activated ion hopping accelerates relaxation of the stored state. This temperature-dependent retention behavior enables a thermally tunable fading memory response, where the persistence of the optically induced conductance state can be controlled through ionic dynamics. These results highlight how opto-ionic coupling at 2D/dielectric interfaces can introduce stimulus-responsive functionality in transistor architectures, providing a platform for devices that combine sensing and memory behavior within the gate stack.