Heterojunction Tunnel Diodes

Owing to the strong Coulomb interaction between electrons and holes, electron tunneling between individual layers of a van der Waals heterostructure may give rise to highly unusual phenomena not observed in conventional materials. Here we report on optoelectronic transport of encapsulated WS₂ – MoSe₂ tunneling heterojunctions, in which we observe anomalous photoconductance and strong rectification. Using Multi-Parameter Dynamic Photoresponse Microscopy, we generate ~10^X photocurrent images of the heterostructure photoresponse as a function of source-drain voltage, gate voltage, and temperature. Alongside strong rectifying behavior, we observe an anomalous reduction in the interlayer conductance that is tunable with gate voltage and temperature. This behavior becomes significantly enhanced with optical illumination, allowing us to assess the interactions of electrons and holes at the heterostructure interface. Our measurements indicate that strong two-body correlations arise precisely at the onset to a reduction in tunneling conductance, which we speculate is a signature of the crossover from free electron to bound interlayer exciton state.