An electrically controlled interlayer exciton trap

The formation of robust interlayer excitons in van der Waals (vdW) heterostructures requires a staggered band alignment, where electrons and holes are separated across two constituent layers. In WS₂-MoSe₂ heterostructures the close proximity of conduction band edges suggests that fine electrical tuning may be used to selectively trap or dissociate such excitons. Here, we report ultrafast photocurrent imaging studies of WS₂-MoSe₂ heterojunction devices using Multi-Parameter Dynamic Photoresponse Microscopy.  We generate photocurrent images of the heterojunction response as a function of source-drain and gate voltages, laser power, and photon energy. We observe strong negative differential photoconductance (NDC) that evolves with source-drain and gate voltages. NDC occurs simultaneously with a peak in the two-body interaction rate within the junction. Moreover, we find that the interlayer exciton photocurrent resonance is highly sensitive to precise voltage tuning. Combining these effects we establish the phase space for robust interlayer exciton formation in WS₂-MoSe₂ heterojunctions. Our results highlight how heterojunction band alignment can be finely tuned to trap or dissociate interlayer excitons, providing a key stepping stone for vdW exciton quantum simulators.