High-responsivity graphene infrared photodetectors based on photogating

Graphene is a promising material for next-generation high-performance photodetectors because of its fast response, broadband photodetection (from the ultraviolet region to the terahertz region), mechanical and chemical stability, flexibility, and low manufacturing cost. We developed high-responsivity graphene infrared (IR) photodetectors based on field-effect transistors (FETs) with photogating that operate in the middle- or long-wavelength IR (MWIR or LWIR) region. The photogating effect is induced by a photosensitizer located in the vicinity of graphene. The photosensitizer generates a voltage change via incident light, which modulates the carrier density of graphene and produces an extremely large differential output current. This effect, unique to graphene, is attributed to its high carrier mobility and single-atom thickness. As photosensitizers, InSb and LiNO3 were used for the MWIR and LWIR regions, respectively. However, graphene FET-based structures inevitably produce a large dark current because graphene has no bandgap. This degenerates photodetector performance and prevents the construction of IR image sensors using conventional readout integrated circuits. To overcome this problem, a graphene/InSb heterostructure is proposed. It exhibits both a low dark current and a high responsivity by amplifying injected photocarriers via photogating in the MWIR region. These results can be applied to other wavelength regions and could contribute to the development of high-performance graphene-based IR image sensors and next-generation optoelectronic devices.