posted on 2020-03-24, 15:35authored byKyrylo Greben, Sonakshi Arora, Moshe G. Harats, Kirill I. Bolotin
We
investigate the excitonic peak associated with defects and disorder
in low-temperature photoluminescence of monolayer transition metal
dichalcogenides (TMDCs). To uncover the intrinsic origin of defect-related
(D) excitons, we study their dependence on gate voltage, excitation
power, and temperature in a prototypical TMDC monolayer MoS2. Our results suggest that D excitons are neutral excitons bound
to ionized donor levels, likely related to sulfur vacancies, with
a density of 7 × 1011 cm–2. To study
the extrinsic contribution to D excitons, we controllably deposit
oxygen molecules in situ onto the surface of MoS2 kept at cryogenic temperature. We find that, in addition
to trivial p-doping of 3 × 1012 cm–2, oxygen affects the D excitons, likely by functionalizing the defect
sites. Combined, our results uncover the origin of D excitons, suggest
an approach to track the functionalization of TMDCs, to benchmark
device quality, and pave the way toward exciton engineering in hybrid
organic–inorganic TMDC devices.