Dual-mode G–aSi–ITO transparent photodetectors enabled by optical switching of defect states

Abstract

Optically transparent graphene–amorphous silicon–ITO (G–aSi–ITO) photodetectors operate in two distinct modes—high responsivity mode (HRM) and high-speed mode (HSM)—effectively overcoming the intrinsic limitations of amorphous silicon-based photodetectors caused by its high defect density and low carrier mobility. The active layer is composed of non-hydrogenated, undoped amorphous silicon films with a thickness of 300 nm, ensuring both short carrier transit times for typical photogenerated carriers and high optical transparency in the visible spectrum. In this study, we demonstrate that the role of deep-level defect states can be optically modulated to enable dual-mode operation. In HRM, photogenerated carrier loss is minimized by suppressing recombination while allowing for carrier trapping and detrapping via highly localized deep-level states. Conversely, HSM is achieved by optically activating these defect states to enhance recombination, thereby reducing responsivity but enabling faster operation. These dual-mode transparent photodetectors are particularly efficient for low optical power detection.