Infrared photodetector based on photo-thermionic effect of graphene-nanowalls/silicon heterojunction.

Due to the slow relaxation process according to weak acoustic phonon interaction, photo-thermionic effect in graphene could be much more obvious than metal film, so graphene heterojunction photodetector based on photo-thermionic effect is promising for infrared imaging applications. However, the 2.3% absorption rate of graphene film presents a severe limitation. Here, in-situ grown graphene nanowalls (GNWs) were integrated on silicon substrate interfaced with Au nanoparticles. Due to the strong infrared absorption and hot-carrier relaxation process in GNWs, 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 specific detectivity of 1.4×1010 cm Hz1/2/W and 1.6×109 cm Hz1/2/W based on calculated and measured noise respectively in 1550 nm at room temperature, which has best performance among silicon-compatible infrared photodetectors without any complicated waveguide structures. Obvious photoresponse are also detected in the mid-infrared and terahertz band. The interface Au particle are found to reduce the barrier height and enhance absorption. The device structure in this report could be compatible with semiconductor process, so infrared photodetectors with high integration density and low cost could be potentially realized.