In
optoelectronic devices based on two-dimensional (2D) semiconductor
heterojunctions, the efficient charge transport of photogenerated
carriers across the interface is a critical factor to determine the
device performances. Here, we report an unexplored approach to boost
the optoelectronic device performances of the WSe2–MoS2
p–n heterojunctions
via the monolithic-oxidation-induced doping and resultant modulation
of the interface band alignment. In the proposed device, the atomically
thin WO
x
layer, which is directly formed
by layer-by-layer oxidation of WSe2, is used as a charge
transport layer for promoting hole extraction. The use of the ultrathin
oxide layer significantly enhanced the photoresponsivity of the WSe2–MoS2
p–n junction devices, and the power conversion efficiency
increased from 0.7 to 5.0%, maintaining the response time. The enhanced
characteristics can be understood by the formation of the low Schottky
barrier and favorable interface band alignment, as confirmed by band
alignment analyses and first-principle calculations. Our work suggests
a new route to achieve interface contact engineering in the heterostructures
toward realizing high-performance 2D optoelectronics.
Excitons, electron–hole pairs in semiconductors,
can be
utilized as information carriers with a spin or valley degree of freedom.
However, manipulation of excitons’ motion is challenging because
of their charge-neutral characteristic and short recombination lifetimes.
Here we demonstrate electric-field-driven drift and funneling of charged
excitons (i.e., trions) toward the center of a MoSe2 monolayer.
Using a simple bottom-gate device, we control the electric fields
in the vicinity of the suspended monolayer, which increases the trion
density and pulls down the layer. We observe that locally excited
trions are subjected to electric force and, consequently, drift toward
the center of the stretched layer. The exerting electric force on
the trion is estimated to be 102–104 times
stronger than the strain-induced force in the stretched monolayer,
leading to the successful observation of trion drift under continuous-wave
excitation. Our findings provide a new route for manipulating trions
and achieving new types of optoelectronic devices.
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