Broadband Photoresponse from Asymmetric Hot-Carrier Thermalizations in Atomically Thin Lateral Heterojunctions

The massless Dirac electron transport in graphene makes electron-electron scatterings much faster than the electron-phonon scatterings that dominate conventional semiconducting materials. This leads to an ultrafast (~ps) hot-carrier induced photothermoelectric (PTE) photoresponse, which is very promising for optical communications. However, it becomes more challenging to further optimized the devices, mainly because the spectral range, thermoelectric power factor, and the electron-phonon coupling strength are all coupled to the Fermi level of graphene. Here we proposed an asymmetric lateral heterojunction PTE photodetector that decouples the optimization of the spectral range and the responsivity. As a proof of concept, we synthesized graphene-MoS₂ lateral heterojunctions through seed molecule selective “sowing” method and the as-fabricated devices showed broadband (400 nm to 1.6 µm) response, and good electrostatic gating tunability. The device behaviors can be explained through large discrepancies of the gate-tunable thermal relaxation pathways on the two sides of the asymmetric junction. Our proposed structure provided a new platform for the study of hot electron transport in strong electron-correlated systems and paved a way for high-performance, broadband photodetectors.