Ultrasensitive all-2D MoS2 phototransistors enabled by an out-of-plane MoS2 PN homojunction

Abstract Two-dimensional transition metal dichalcogenide-based photodetectors have demonstrated potential for the next generation of 2-dimensional optoelectronics. However, to date, their sensitivity has not been superior to that of other technologies. Here we report an ultrasensitive two-dimensional photodetector employing an in-plane phototransistor with an out-of-plane vertical MoS 2 p–n junction as a sensitizing scheme. The vertical built-in field is introduced for the first time in the transport channel of MoS 2 phototransistors by facile chemical surface doping, which separates the photo-excited carriers efficiently and produces a photoconductive gain of &gt;10 5 electrons per photon, external quantum efficiency greater than 10%, responsivity of 7 × 10 4 A W −1 , and a time response on the order of tens of ms. This taken together with a very low noise power density yields a record sensitivity with specific detectivity $$D^*$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msup> </mml:math> of 3.5 × 10 14 Jones in the visible and a broadband response up to 1000 nm.

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