Self-Powered 2D MoS2/WOx/WSe2 Heterojunction Photodetector Realized by Oxygen Plasma Treatment

2D transition metal dichalcogenides (TMDCs) are anticipated to be the ones of future nano-sized photodevices due to their electronic and optoelectronic properties. They have shown remarkable performances as photodetectors from being fabricated into heterostructures with p-n junction. An oxygen plasma-doped WSe2/pristine MoS2-based photodetector with high responsivity and broad detection spectrum ranging from visible to near-infrared (NIR) region is reported. The oxygen plasma treatment forms a WOx layer on WSe2 that not only acts as a p-dopant but also an interfacial oxide layer to suppress dark current to as low as approximate to pA. Under illumination of visible light (520 nm in this study), greatly enhanced photoresponsivity and specific detectivity of thus fabricated devices are achieved without applying an external bias, in contrast to untreated devices. The devices have also exhibited good photodetection in the NIR region with two orders enhanced photoresponsivity under the illumination of 852 nm light at room temperature. It is confirmed from photomapping measurements that the photocurrent is mainly generated from p-n heterojunction. These results indicate that oxygen plasma-doped WSe2-based heterojunctions can be used as highly sensitive and self-powered photodetectors.