Enhancement of Out-of-Plane Charge Transport in a Vertically Stacked Two-Dimensional Heterostructure Using Point Defects.

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 through controllable formation of point defects, thus enhancing 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 top atomic layer of WSe2 with controllable density via Ga ion irradiation. The interlayer charge transport in the W/G heterostructure was detected with femtosecond 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 photoinduced interlayer charge transfer from WSe2 to graphene. Based on this feature, a photodetector based on W/G modified by point defects is proposed and implemented, exhibiting a fast photoresponsivity (∼0.6 ms) (2 orders of magnitude larger than the photoresponse in pristine W/G). This work demonstrates that out-of-plane charge transport is enhanced by the presence of point defects and illustrates an efficient method to optimize the performance of photoelectric devices based on vertical heterostructures.