Ultralocalized Optoelectronic Properties of Nanobubbles in 2D Semiconductors

The major contributors to achieving localized optical emitters in transition-metal dichalcogenides materials at the nanoscale have been previously unclear and a robust experimental picture relating the local electronic structure with emission properties in such structures has so far been lacking. We use a combination of scanning tunneling microscopy (STM) and near-field photoluminescence (nano-PL) to probe the electronic and optical properties of single nanobubbles in bilayer heterostructures of WSe2 on MoSe2. We show from tunneling spectroscopy that there are electronic states deeply localized in the gap at the edge of such bubbles. We also show a significant change in the local band gap on the bubble, with a continuous evolution to the edge of the bubble. Nano-PL measurements observe a continuous redshift of the interlayer exciton on entering the bubble, in agreement with the band-to-band transitions measured by STM. We use self-consistent Schro¨dinger-Poisson simulations to capture the essence of the experimental results and find that strong doping in the bubble region is a key ingredient to achieving the observed localized states, together with mechanical strain.