THz-circuits driven by photo-thermoelectric graphene-junctions

TL;DR

This paper demonstrates that dual-gated graphene junctions can be integrated into THz circuits utilizing ultrafast photo-thermoelectric currents, advancing nanoscale high-frequency optoelectronic device capabilities.

Contribution

It introduces the use of dual-gated graphene junctions as functional components in THz circuits based on ultrafast photo-thermoelectric effects, highlighting new ultrafast optoelectronic mechanisms.

Findings

Immediate photo-thermoelectric current observed after femtosecond laser excitation.

A second, inverted photo-thermoelectric contribution appears on picosecond timescales.

Ultrafast electromagnetic transients are generated in high-frequency circuits due to these effects.

Abstract

For future on-chip communication schemes, it is essential to integrate nanoscale materials with an ultrafast optoelectronic functionality into high-frequency circuits. The atomically thin graphene has been widely demonstrated to be suitable for photovoltaic and optoelectronic devices because of its broadband optical absorption and its high electron mobility. Moreover, the ultrafast relaxation of photogenerated charge carriers has been verified in graphene. Here, we show that dual-gated graphene junctions can be functional parts of THz-circuits. As the underlying optoelectronic process, we exploit ultrafast photo-thermoelectric currents. We describe an immediate photo-thermoelectric current of the unbiased device following a femtosecond laser excitation. For a picosecond time-scale after the optical excitation, an additional photo-thermoelectric contribution shows up, which exhibits the fingerprint of a spatially inverted temperature profile. The latter can be understood by the different time-constants and thermal coupling mechanisms of the electron and phonon baths within graphene to the substrate and the metal contacts. The interplay of the processes gives rise to ultrafast electromagnetic transients in high-frequency circuits, and it is equally important for a fundamental understanding of graphene-based ultrafast photodetectors and switches.