Signatures of defect-localized charged excitons in the photoluminescence of monolayer molybdenum disulfide

We study spatial photoluminescence characteristics of neutral and charged excitons across extended monolayer MoS$_2$ synthesized by chemical vapor deposition. Using two-dimensional hyperspectral photoluminescence mapping at cryogenic temperatures we identify regions with increased emission from charged excitons associated with both spin-orbit split valence subbands. Such regions are attributed to unintentional doping at defect sites with excess charge that bind neutral excitons to form defect-pinned trions. Our findings imply comparable timescales for the formation, relaxation, and radiative decay of $B$ trions, and add defect-localized $A$ and $B$ trions to the realm of photoexcited quasiparticles in layered semiconductors.