posted on 2021-09-22, 17:05authored byYanran Liu, Yue Liu, Hua Zhou, Zaixing Yang, Yuanyuan Qu, Yang Tan, Feng Chen
Defects
are ubiquitous in two-dimensional (2D) transition-metal
dichalcogenides (TMDs), generated by the initial growth- or the postprocessing.
However, the defects may play negative roles in the photoelectronic
properties of TMDs due to the reduction of in-plane transport of carriers.
In this work, we demonstrate that the Se-vacancy
defects in MoSe2 side of the van der Waal heterostructure
is able to switch direction of out-of-plane charge transport. Photoresponse
spectra showed defect density enable modified surface potential of
MoSe2–x, leading to the barrier
reverse between graphene and MoSe2–x and switches of the photoresponse from the negative to the positive.
This unexpected property stemmed from appearance of midgap states
by defects at heterostructure, as demonstrated by the density functional
theory calculation and scanning tunneling microscope results. MoSe2–0.2/graphene heterostructure has a broadband response
ranging from 450 to 1064 nm and exhibits comparable or higher positive
responsivity (5.4 × 103 A/W to −15.3 ×
103 A/W at 632.8 and 5.7 × 103 A/W to −1.2
× 103 A/W at 1064 nm) to the negative one of the pristine
MoSe2/graphene. Based on defect-engineered heterostructures,
we construct optoelectronic OR and AND logic devices with a broadband
operation. Our work elucidates an alternative avenue to tailor the
out-of-plane charge transport in TMD-based heterostructure through
defects, and potentially invokes applicable utilization for 2D photodetectors
and optoelectronic logic gates.