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Graphene has remarkable optoelectronic properties and thus would represent a means to improve infrared (IR) photodetectors. As a result of its Dirac-cone structure, graphene exhibits broadband light absorption and a rapid response. Unlike quantum photomaterials, graphene can also be synthesized inexpensively via a non-toxic process. Despite these advantages, graphene-based photodetectors suffer from low responsivity due to the low absorption of graphene of around 2.3%. Therefore, there is a strong demand to enhance the IR responsivity of graphene photodetectors and expand the range of IR applications. In this study, enhancement of the middle-wavelength IR (MWIR) photoresponsivity of graphene photodetectors using the photogating effect was investigated. The photo-gating effect is induced by photosensitizers, which are located around the graphene channel and couple incident light and generate a large electrical change. The graphenebased MWIR photodetectors consisted of a top graphene channel, source-drain electrodes, insulator layer, and photosensitizer. The photoresponse characteristics were investigated through current measurements using a device analyzer. The device was vacuum-cooled and the graphene channel was irradiated with light from a MWIR laser. The device exhibited a clear MWIR photoresponse observed as modulation of the output current during irradiation. The MWIR photoresponse with the photo-gating effect was 100 times higher than that of conventional graphene photodetectors without the photo-gating effect. The device maintained its MWIR photoresponse at temperatures up to 150 K. The results obtained in this study will contribute to the development of high-performance graphene-based IR image sensors.
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