Indexed on: 20 Sep '18Published on: 20 Sep '18Published in: ACS Nano
Point defects in 2D materials block in-plane charge transport, which incurs negative effects on the photoresponse of 2D monolayer materials. In contrast to in-plane charge transport, we show that out-of-plane charge transport in 2D materials can be enhanced via controllable formation of point defects, thus benefiting the photoresponse of a vertical heterostructure. Graphene and WSe2 monolayers were stacked together to construct a vertical heterostructure (W/G). Se point defects were artificially formed on the upper atomic layer of WSe2 with controllable density via Ga ion irradiation. The interlayer charge transport in the W/G heterostructure was detected with fs optical probe-pump measurements and photoelectric detection. Our experiments show that point defects can be used to provide higher transfer rate for out-of-plane charge transport and more electronic states for photoexcitation, leading to enhanced photo-induced interlayer charge transfer from WSe2 to graphene. According to this phenomenon, we present a photodetector based on W/G modified by point defects. This structure exhibits fast photoresponsivity (~ 0.6 ms) that is 2 orders of magnitude larger than the photoresponse in pristine W/G. Our work demonstrates that out-of-plane charge transport is enhanced by the presence of point defects and illustrates a novel method for optimizing the performance of photoelectric devices based on vertical heterostructures.