Two-dimensional (2d) transition-metal dichalcogenides (TMDCs) are promising candidate materials for developing next generation nano optoelectronic devices, due to their strong interaction with light. In addition, the free of surface dangling bonds makes it possible to stacking any different types of 2D TMDCs together to form heterojunctions with desirable band structures for various applications. However, most of the 2D TMDCs are bipolar or strong unipolar n-type doped, while very few of them show weak p-type doping, which severely affects the performance of the formed heterojunctions. In this work, we fabricated a SnSe2/WSe2 heterojunction of type II band alignment with a small bandgap of ~0.1 eV, which is ideally for developing optoelectronic devices responsible to a broad light spectrum. N2O plasma treatment is applied to enhance the p-type doping of both WSe2 and SnSe2, which results in the increased on-off ratio of n-type SnSe2 by 50 times and the hole mobility of WSe2 by 527 times. The WSe2/SnSe2 heterostructure also achieves a decent performance as a p-n junction, which exhibits photo responsivity of 450 mA/W and 133 mA/W for 700 nm visible light and 1600 nm infrared light, respectively, without any gate or source-drain bias, showing great photovoltaic effect. Moreover, the heterojunction shows great promise as an artificial visual neuron, which can differentiate the dark, visible and infrared light illumination conditions by applying a series of electrical pulses through the back-gate electrode.
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