Acoustic phonon recycling for photocarrier generation in graphene-WS2 heterostructures

Electron-phonon scattering is the key process limiting the efficiency of modern nanoelectronic and optoelectronic devices, in which most of the incident energy is converted to lattice heat and finally dissipates into the environment. Here, we report an acoustic phonon recycling process in graphene-WS2 heterostructures, which couples the heat generated in graphene back into the carrier distribution in WS2. This recycling process is experimentally recorded by spectrally resolved transient absorption microscopy under a wide range of pumping energies from 1.77 to 0.48 eV and is also theoretically described using an interfacial thermal transport model. The acoustic phonon recycling process has a relatively slow characteristic time (>100 ps), which is beneficial for carrier extraction and distinct from the commonly found ultrafast hot carrier transfer (~1 ps) in graphene-WS2 heterostructures. The combination of phonon recycling and carrier transfer makes graphene-based heterostructures highly attractive for broadband high-efficiency electronic and optoelectronic applications. Here, the authors perform transient absorption microscopy on graphene-WS2 heterostructures, and identify a phonon recycling process that couples the heat generated in graphene back into the carrier distribution in WS2 with a picosecond characteristic time.