Self-powered and bipolar photodetector based on a van der Waals metal-semiconductor junction:Graphene/WSe2/Fe3GeTe2 heterojunction

A self-driven photosensor with signal-reversal response has the potential to work as a photodetector in complex environments with multiple signals owing to better signal recognition and enhanced signal-processing efficiency.Herein,a metal-semiconductor-metal photodetector based on ambipolar WSewith two electrodes comprising two-dimensional(2 D) van der Waals(vdWs) metal FeGeTeand semimetal graphene was proposed to form an asymmetrical metal-contacted architecture with different Schottky barrier heights.The regulating gate field-induced Fermi level shift in WSecan be used to manipulate the WSechannel’s carrier type,resulting in a polarity-reversible photodetector without a bias voltage.Furthermore,the photovoltaic effect can be observed from wavelengths of 450 nm(visible) to 850 nm(infrared) without external voltage.The large open voltage is -0.177 V and short-circuit current is 17 nA under a 650-nm excitation wavelength.The reported WSe-based photodetector exhibits excellent properties under zero bias,including a large photo-to-dark current ratio greater than 10~6 with dark current less than 1 fA,photovoltaic performance with an external quantum efficiency of 27.14%,an excellent detectivity of 3.4×10Jones,and a high responsivity of 116.38 mA/W.Rapid electron transfer occurs at the interface between WSeand vd Ws electrodes,resulting in a 370-μs response speed owing to the clean and nondestructive interfaces between vd Ws metals and WSe.This study demonstrates the wide application prospect of the vd Ws metal FeGeTeas an electrode forming a Schottky junction for realizing a photodetector without an external voltage and accelerates the development of 2 D photosensors with various working modes.