  Substitutionally doped transition metal dichalcogenides (TMDs) are the next
step towards realizing TMD-based field effect transistors, sensors, and quantum
photonic devices. Here, we report on the influence of Re concentration on
charge doping and defect formation in MoS2 monolayers grown by metal-organic
chemical vapor deposition. Re-MoS2 films can exhibit reduced sulfur-site
defects; however, as the Re concentration approaches 2 atom%, there is
significant clustering of Re in the MoS2. Ab Initio calculations indicate that
the transition from isolated Re atoms to Re clusters increases the ionization
energy of Re dopants, thereby reducing Re-doping efficacy. Using
photoluminescence spectroscopy, we show that Re dopant clustering creates
defect states that trap photogenerated excitons within the MoS2 lattice. These
results provide insight into how the local concentration of metal dopants
affect carrier density, defect formation, and exciton recombination in TMDs,
which can aid the development of future TMD-based devices with improved
electronic and photonic properties.
