Photo-Thermoelectric Response in Graphene/h-BN Heterostructures Induced by Interface Thermal Asymmetry for Enhanced Photodetection

As integrated circuits continue to scale down, nanoscale thermal management devices have become critically important as thermal management solutions. Photothermoelectric (PTE) detection offers a promising route toward broadband, self-powered photodetectors, yet the response is usually achieved through external gating or engineered junctions. Here, we demonstrate robust, bias-free photodetection in an h-BN/graphene/h-BN van der Waals heterostructure by exploiting the intrinsic interfacial asymmetry between partially encapsulated and bare graphene regions. Without any applied bias, spatially localized PTE currents are produced by discontinuities in the Seebeck coefficient and thermal conductivity at the h-BN edges. The result is attributed to a phonon-mediated mechanism: the top h-BN layer preferentially suppresses out-of-plane (ZA) phonon modes in graphene, lowering in-plane thermal conductivity and increasing the temperature differential across the interface. Photocurrent mapping measurements and finite-difference time-domain simulations show that the geometry and thickness of the h-BN capping layer can be used to adjust the photocurrent’s magnitude and the spatial profile. Our findings establish interfacial phonon engineering as an effective strategy for tailoring local thermoelectric fields and open a path toward developing embedded, self-powered thermal sensors for next-generation electronic chips.