Realizing precise charge neutrality in van der Waals heterostructure p-n junctions through data intensive photoresponse imaging

In atomically thin materials, the narrow phase space for exciton–phonon interactions could be used to engineer unusual devices that mimic molecular optical transitions. A van der Waals heterostructure tuned to a charge neutral state allows for the formation of excitons where the electron and hole are localized in different materials. Such interlayer excitons have a well-defined dipole moment making them sensitive to the interlayer electric field and out-of-plane vibrations. To isolate the behavior of interlayer excitons and explore their dynamics, we employ Multi-Parameter Dynamic Photoresponse Microscopy on encapsulated heterostructures composed of monolayer MoSe₂ and bilayer WSe₂. Gathering a large set of spatial photocurrent images as a function of source-drain and gate voltages, we unambiguously identify the charge neutrality condition. We observe that the system can be tuned to exhibit clear rectification with highly uniform spatial dependence in the heterojunction consistent with the formation of a two-dimensional distributed p-n junction at charge neutrality. Under these precise charge neutrality conditions, we observe striking spectroscopic features that reveal highly unusual exciton-phonon interactions.