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Self‐powered photodetectors have attracted widespread attention due to their low power consumption which can be driven by the built‐in electric field instead of external power, but it is very difficult to achieve high responsivity and fast response speed concurrently. Here, a self‐powered photodetector with light‐induced electric field enhancement based on a 2D InSe/WSe2/SnS2 van der Waals heterojunction is designed. The light‐induced electric field derived from the photo‐generated electrons of SnS2 accumulated at the SnS2/WSe2 interface produces an additional negative gate voltage applied to the WSe2 layer, which enhances the built‐in electric field in the InSe/WSe2/SnS2 heterojunction. Accordingly, the photocurrent and photoresponse speed of the heterostructure device are largely improved. The self‐powered photodetector based on the InSe/WSe2/SnS2 heterostructure exhibits a high responsivity of 550 mA W−1, which is a 50 times increase compared to the InSe/WSe2 photodetector, and the response speed (110/120 µs) is one order of magnitude faster than that of the InSe/WSe2 photodetector. The high responsivity and fast speed are caused by the stronger built‐in electric field modulated by a light‐induced electric field, which can separate carriers effectively and reduce drift times. This device architecture can provide a new avenue to fabricate high‐responsivity, fast self‐power photodetectors by utilizing the van der Waals heterojunction. [ABSTRACT FROM AUTHOR]

2D materials, with their extraordinary physical and chemical properties, have gained extensive interest for physical, chemical and biological sensing applications. However, 2D material‐based devices, such as field effect transistors (FETs) often show high contact resistance and low output signals, which severely affect their sensing performance. In this study, a new strategy is developed to combine metallic and semiconducting polymorphs of transition‐metal dichalcogenides (TMDCs) to solve this critical issue. Such a phase engineering methodology to integrate large‐scale and spatially assembled multilayers of 2H MoTe2 FETs with coplanar metallic 1T′ MoTe2 contacts is applied. Such in‐plane heterophase‐based FETs exhibit an ohmic contact behavior with an extremely low contact resistance due to the coplanar and seamless connections between 2H and 1T′ phases of MoTe2. These 1T′/2H/1T′ based FETs are successfully demonstrated for detecting NH3 with high current outputs increased up to microamp levels without using any conventional interdigital electrodes, which is compatible with the current CMOS circuits for practical applications. Furthermore, the as‐fabricated sensors can detect NH3 gas concentrations down to 5 ppm at room temperature. This study demonstrates a new strategy of applying the heterophase MoTe2‐based nanoelectronics for high‐performance sensing applications. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) synaptic devices integrate NIR optical sensitivity and synaptic plasticity, emulating the basic biomimetic function of the human visual system and showing great potential in NIR artificial vision systems. However, the lack of semiconductor materials with appropriate band gaps for NIR photodetection and effective strategies for fabricating devices with synaptic behaviors limit the further development of NIR synaptic devices. Here, a two-terminal NIR synaptic device consisting of the In 2 Se 3 /MoS 2 heterojunction has been constructed, and it exhibits fundamental synaptic functions. The reduced band gap and potential barrier of In 2 Se 3 /MoS 2 heterojunctions are essential for NIR synaptic plasticity. In addition, the NIR synaptic properties of In 2 Se 3 /MoS 2 heterojunctions under strain have been studied systematically. The ΔEPSC of the In 2 Se 3 /MoS 2 synaptic device can be improved from 38.4% under no strain to 49.0% under a 0.54% strain with a 1060 nm illumination for 1 s at 100 mV. Furthermore, the artificial NIR vision system consisting of a 10 × 10 In 2 Se 3 /MoS 2 device array has been fabricated, exhibiting image sensing, learning, and storage functions under NIR illumination. This research provides new ideas for the design of flexible NIR synaptic devices based on 2D materials and presents many opportunities in artificial intelligence and NIR vision systems.