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A type of broadband (325−980 nm) self-powered photodetector based on graphene/GaAs van der Waals heterojunction is reported. By simply spinning a layer of Ag nano-particles (Ag NPs) onto graphene/GaAs heterostructure, the responsivity and detectivity of our devices for the whole spectrum range are enhanced significantly. The maximum photocurrent responsivity of 210 mA W−1 (increased by 38%) and detectivity of 2.98 × 1013 Jones (increased by 202%) are achieved at 405 nm, which is about two or three orders of magnitude larger than other graphene based self-powered photodetectors. The mechanism of the improvement originates from the overlap the depletion region of graphene/GaAs heterostructure, the surface plasmon enhanced light field region below the surface and the light absorption region of the GaAs layer. The external quantum efficiency (EQE) measurement, transient photoluminescence (PL) test and the comparative theoretical simulation show that the surface plasmon enhancement should only be applicable for graphene/direct band gap semiconductor heterostructure, where the semiconductor should have a high optical absorption coefficient. The obtained high performance broadband photodetector with excellent detectivity is a promising candidate for many important optoelectronic applications, such as ultrasensitive image sensor in charge coupled displayer field, which requires colour sensors not only with high photo responsivity but also in a wide spectral range.

Summary Light-excited energetic electrons, or so-called hot electrons (HEs), in plasmonic metal nanostructures have received much attention in the past few years. Plasmonic metal nanostructures, acting as light absorbers with higher efficiency and adjustability than dye molecules and inorganic semiconductors, can generate HEs under specific light conditions. However, the overall efficiency of the plasmonic systems remain unsatisfactory. Therefore, it is important to study the generation and transfer processes of plasmon-induced HEs, which are necessary for efficient plasmon-enhanced applications. In this review, we summarize the basic concepts and mechanisms of HE generation and transportation, then highlight the use of in situ surface-enhanced Raman spectroscopy (SERS) as a probe for HE-induced chemical reactions. We also discuss the opportunities and remaining challenges in promoting fundamental understanding of, and practical applications for, HEs.