Shallow Impurity States in Doped Silicon Substrates Enabling High Responsivity for Graphene Mid-Infrared Photodetectors

The practical realization of optoelectronic devices operating in the mid-infrared region is stimulated by both fundamental interests and applications ranging from spectroscopy, sensing, imaging, and security to communications. Despite significant achievements in semiconductors, essential barriers including the cryogenic operation and complicated growth processes prevent the applications of mid-infrared detectors. Graphene is widely used in modern electronics, but its low absorption limits photodetection. It is therefore of interest to extend the performance of graphene photodetectors into the mid-infrared region. Here, we first demonstrate pure graphene photodetectors operating in a broadband range from the deep ultraviolet to the mid-infrared region by utilizing photoionization of shallow impurities and over band gap excitation in highly doped Si:B and Si:P substrates. We have observed a photoresponsivity of ∼5 A/W under the mid-infrared illumination at room temperature. This approach paves the way for a concept of dual-photogating effect induced by both highly doped Si substrates and nanomaterials/nanostructures on top of graphene field-effect transistors.