Photovoltaic effects in reconfigurable heterostructured black phosphorus transistors

We demonstrate a reconfigurable black phosphorus electrical field transistor,which is van der Waals heterostructured with few-layer graphene and hexagonal boron nitride flakes.Varied homojunctions could be realized by controlling both source–drain and top-gate voltages.With the spatially resolved scanning photocurrent microscopy technique,photovoltaic photocurrents originated from the band-bending regions are observed,confirming nine different configurations for each set of fixed voltages.In addition,as a phototransistor,high responsivity(～800 mA/W)and fast response speed(～230μs)are obtained from the device.The reconfigurable van der Waals heterostructured transistors may offer a promising structure towards electrically tunable black phosphorus-based optoelectronic devices.

Chip-integrated van der Waals PN heterojunction photodetector with low dark current and high responsivity

Two-dimensional materials are attractive for constructing high-performance photonic chip-integrated photodetectors because of their remarkable electronic and optical properties and dangling-bond-free surfaces.However,the reported chip-integrated two-dimensional material photodetectors were mainly implemented with the configuration of metalsemiconductor-metal,suffering from high dark currents and low responsivities at high operation speed.Here,we report a van der Waals PN heterojunction photodetector,composed of p-type black phosphorous and n-type molybdenum telluride,integrated on a silicon nitride waveguide.The built-in electric field of the PN heterojunction significantly suppresses the dark current and improves the responsivity.Under a bias of 1 V pointing from n-type molybdenum telluride to p-type black phosphorous,the dark current is lower than 7 nA,which is more than two orders of magnitude lower than those reported in other waveguide-integrated black phosphorus photodetectors.An intrinsic responsivity up to 577 mA W^(−1) is obtained.Remarkably,the van der Waals PN heterojunction is tunable by the electrostatic doping to further engineer its rectification and improve the photodetection,enabling an increased responsivity of 709 mA W^(−1).Besides,the heterojunction photodetector exhibits a response bandwidth of~1.0 GHz and a uniform photodetection over a wide spectral range,as experimentally measured from 1500 to 1630 nm.The demonstrated chip-integrated van der Waals PN heterojunction photodetector with low dark current,high responsivity and fast response has great potentials to develop high-performance on-chip photodetectors for various photonic integrated circuits based on silicon,lithium niobate,polymer,etc.