▎ 摘　　要

The proximal coupling between graphene and transition-metal-oxide heterostructures may integrate their unique features and further generate emergent states. Using the photoconductivity of graphene as an effective probe, we demonstrate the existence of a built-in polar field within the LaAlO3 layer of the LaAlO3/SrTiO3 heterostructures for both conducting and insulating LaAlO3/SrTiO3 interfaces. Such a polar field is a prerequisite for the validity of the electronic reconstruction mechanism for the interfacial conductivity. The built-in polar field is reflected by the hole doping in the graphene in proximity to the LaAlO3/SrTiO3 induced by pulsed deep-ultraviolet illumination regardless of the graphene's carrier type. These photoresponse characteristics also render the graphene/LaAlO3/SrTiO3 hybrid system a convenient deep-ultraviolet sensor. Moreover, we design an efficient broad-spectrum photodetector benefiting from the large in-plane electric field in graphene across the boundary between the graphene/LaAlO3/SrTiO3 and graphene/SrTiO3. Our findings may provide clues to the design of photosensors based on the hybrid structures of graphene and oxide heterostructures.