Deciphering photocurrent mechanisms at the nanoscale in van der Waals interfaces for enhanced optoelectronic applications.

Integrated photodetectors are vital for their high speed, sensitivity, and low power consumption, with photocurrent driven by the photovoltaic and photothermoelectric (PTE) effects. At the nanoscale, these mechanisms overlap, complicating their separate evaluation. We introduce a 3D photocurrent nanoimaging technique to map these effects in a MoS-Au Schottky photodiode, revealing a PTE-dominated region extending hundreds of nanometers from the electrode edge, enabled by weak electrostatic forces in two-dimensional materials. Unexpectedly, adding high-thermal conductivity hexagonal boron nitride enhances the PTE response by laterally redirecting heat, aligning thermal gradients with Seebeck coefficient variations, and boosting local conductance. This technique advances optoelectronic applications and deepens insights into light-matter interactions in low-dimensional systems, offering a powerful tool for designing efficient nanoscale photodetectors.