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For future on-chip communication schemes, it is essential to integratenanoscale materials with an ultrafast optoelectronic functionality intohigh-frequency circuits. The atomically thin graphene has been widelydemonstrated to be suitable for photovoltaic and optoelectronic devices becauseof its broadband optical absorption and its high electron mobility. Moreover,the ultrafast relaxation of photogenerated charge carriers has been verified ingraphene. Here, we show that dual-gated graphene junctions can be functionalparts of THz-circuits. As the underlying optoelectronic process, we exploitultrafast photo-thermoelectric currents. We describe an immediatephoto-thermoelectric current of the unbiased device following a femtosecondlaser excitation. For a picosecond time-scale after the optical excitation, anadditional photo-thermoelectric contribution shows up, which exhibits thefingerprint of a spatially inverted temperature profile. The latter can beunderstood by the different time-constants and thermal coupling mechanisms ofthe electron and phonon baths within graphene to the substrate and the metalcontacts. The interplay of the processes gives rise to ultrafastelectromagnetic transients in high-frequency circuits, and it is equallyimportant for a fundamental understanding of graphene-based ultrafastphotodetectors and switches.

THz-circuits driven by photo-thermoelectric graphene-junctions