| Summary: | Non-radiative energy transfer (NRET) from quantum dots (QDs) to monolayer MoS<sub>2</sub> has been shown to greatly enhance the photoresponsivity of the MoS<sub>2</sub> photodetector, lifting the limitations imposed by monolayer absorption thickness. Studies were often performed on a photodetector with a channel length of only a few μm and an active area of a few μm<sup>2</sup>. Here, we demonstrate a QD sensitized monolayer MoS<sub>2</sub> photodetector with a large channel length of 40 μm and an active area of 0.13 mm<sup>2</sup>. The QD sensitizing coating greatly enhances photoresponsivity by 14-fold at 1.3 μW illumination power, as compared with a plain monolayer MoS<sub>2</sub> photodetector without QD coating. The photoresponsivity enhancement increases as QD coating density increases. However, QD coating also causes dark current to increase due to charge doping from QD on MoS<sub>2</sub>. At low QD density, the increase of photocurrent is much larger than the increase of dark current, resulting in a significant enhancement of the signal on/off ratio. As QD density increases, the increase of photocurrent becomes slower than the increase of dark current. As a result, photoresponsivity increases, but the on/off ratio decreases. This inverse dependence on QD density is an important factor to consider in the QD sensitized photodetector design.
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