Infrared Photodetector Based on the Photothermionic Effect of Graphene-Nanowall/Silicon Heterojunction

Because of the slow relaxation process according to weak acoustic phonon interaction, the photothermionic effect in graphene could be much more obvious than in the metal film, so a graphene heterojunction photodetector based on the photothermionic effect is promising for infrared imaging applications. However, the 2.3% absorption rate of the graphene film presents a severe limitation. Here, in situ grown graphene nanowalls (GNWs) were integrated on the silicon substrate interfaced with Au nanoparticles. Because of the strong infrared absorption and hot-carrier relaxation process in GNWs, the as-prepared GNWs/Au/silicon heterojunction has a photo to dark ratio of 2 × 10⁴, responsivity of 138 mA/W, and linear dynamic range of 89.7 dB, with a specific detectivity of 1.4 × 10¹⁰ and 1.6 × 10⁹ cm Hz^1/2/W based on calculated and measured noise, respectively, in 1550 nm at room temperature, and has the best performance among silicon-compatible infrared photodetectors without any complicated waveguide structures. Obvious photoresponses are also detected in the mid-infrared and terahertz band. The interface Au particle is found to reduce the barrier height and enhance absorption. The device structure in this report could be compatible with the semiconductor process, so that infrared photodetectors with high integration density and low cost could be potentially realized.