Spatially resolved photoconductivity mapping of MoS₂ / WS₂ lateral heterostructures

The presence of free carriers directly affects the optical properties of transition metal dichalcogenides. For instance, free carriers directly underpin the competition between neutral excitons and carrier-bound trions and they strongly affect radiative and nonradiative decay pathways. However, despite their fundamental importance for TMDs, spatially resolved studies of the carrier distribution and the associated photoresponse remain challenging. Here we use scanning microwave microscopy (SMM, also called microwave impedance microscopy, MIM) to study the spatial carrier distribution in MoS₂/WS₂ lateral heterostructures under dark conditions as well as under illumination with photon energy-resolved narrowband illumination. We find strong spatial variations in the photoconductive response throughout the flakes studied. We further find significant long-term dynamics in the optically generated free carriers that manifest themselves in persistent charging and discharging and are strongly correlated with observed spatial variations in the steady-state photoconductive response. A comparison with spatially resolved photoluminescence mapping reveals excellent agreement between the local conductivity determined by SMM and the interplay between trion and exciton emission characteristics.