Defect-Mediated Electrostatic Decoupling of Memory and Photodetection in a WSe2/Graphene van der Waals Transistor

Two-dimensional optoelectronic devices offer a promising platform for integrating sensing and information storage, yet trap-mediated charge storage often interferes with dynamic photodetection. Here, we demonstrate a multifunctional WSe2/graphene van der Waals transistor that combines intrinsic defect-mediated memory with illumination-induced electrostatic screening. Deep-level defects in WSe2 enable nonvolatile charge storage without an additional floating gate, yielding a memory window of ∼33.2 V and retention beyond 103 s. Meanwhile, the device exhibits self-powered photovoltaic response at representative wavelengths of 460, 520, 640, and 1064 nm, together with a –3 dB cutoff frequency of ∼8.57 kHz. Notably, programming causes negligible changes in the response bandwidth. This behavior is consistent with illumination-enhanced electrostatic screening: trapped charges electrostatically modulate the graphene channel in the dark, whereas illumination is expected to reduce their long-range influence, rendering the optical response largely independent of the stored state. By selecting the readout bias, the same device further supports self-powered sensing and three distinguishable optoelectronic output states. This work provides a low-complexity strategy for integrating memory, sensing, and multistate optoelectronic control in a single two-dimensional heterostructure.