Negative Photoresponses in MoS₂ Flakes Photogated by p-n Junction Diode

Negative photoresponses in photodetectors can find important applications like image AI and image edge detection. In this Letter, we develop a few-layer MoS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> phototransistor photogated by a silicon-based N<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>P junction. Negative photovoltage will be generated on the open-circuit N<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>P junction by grounding the p-type substrate. The negative photovoltage modulates the conductance of the n-type MoS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> flake, creating negative photoconductance in the MoS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> channel. The light-intensity dependent photoresponses are characterized at cryogenic temperatures. The experimental results can be well fitted with the established device theory.