Unusually
high exciton binding energies (BEs), as much as ∼1
eV in monolayer transition-metal dichalcogenides, provide opportunities
for exploring exotic and stable excitonic many-body effects. These
include many-body neutral excitons, trions, biexcitons, and defect-induced
excitons at room temperature, rarely realized in bulk materials. Nevertheless,
the defect-induced trions correlated with charge screening have never
been observed, and the corresponding BEs remain unknown. Here we report
defect-induced A-trions and B-trions in monolayer tungsten disulfide
(WS2) via carrier screening engineering
with photogenerated carrier modulation, external doping, and substrate
scattering. Defect-induced trions strongly couple with inherent SiO2 hole traps under high photocarrier densities and become more
prominent in rhenium-doped WS2. The absence of defect-induced
trion peaks was confirmed using a trap-free hexagonal boron nitride
substrate, regardless of power density. Moreover, many-body excitonic
charge states and their BEs were compared via carrier
screening engineering at room temperature. The highest BE was observed
in the defect-induced A-trion state (∼214 meV), comparably
higher than the trion (209 meV) and neutral exciton (174 meV), and
further tuned by external photoinduced carrier density control. This
investigation allows us to demonstrate defect-induced trion BE localization via spatial BE mapping in the monolayer WS2 midflake
regions distinctive from the flake edges.
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