Spatially and Precisely Controlled Large-Scale and Persistent Optical Gating in a TiOx–MoS2 Heterostructure

Optical gating derived from persistent photodoping is a promising technique that can control the transport behavior of two-dimensional (2D) materials through light modulation. The advantage of photoinduced doping is that the doping can be controlled precisely and spatially by tuning the light intensity and position. As most photoinduced doping methods suffer from a low doping level, persistent, strong photodoping was conducted in this study in TiO_x–MoS₂ heterostructures under ultraviolet (UV) illumination, which precisely controlled the doping to a high level (1.5 × 10¹³ cm^–2) with a trap-mediated mechanism. This mechanism was confirmed by controlling the doping level with various UV pretreatment doses. After photodoping, devices displayed superior mobility, which is a characteristic of the modulation doping used in high-electron-mobility transistors. The modulation doping sites in the inner TiO_x layer were far from the channel surface (MoS₂); thus, the channel was able to preserve its high-mobility property even after doping. This dose-dependent, strong, and persistent photodoping phenomenon can render the TiO_x–MoS₂ heterostructure suitable for use in UV detectors and in nonvolatile light-driven memory products. Moreover, by using spatially controlled light scans, selective photodoping at the contact edges can dramatically reduce the contact resistance without destroying the on–off ratio of the device by forming an n⁺–n–n⁺ channel. Because TiO_x–MoS₂ heterostructures are versatile, they provide a compelling platform for high-performance 2D optoelectronic devices.