Nonlinear response of a ballistic graphene transistor with an ac-driven gate: high harmonic generation and THz detection

TL;DR

This paper investigates the nonlinear electron transport in a ballistic graphene transistor with an ac-driven gate, revealing high harmonic generation and potential applications in THz detection and frequency multiplication.

Contribution

It introduces a theoretical framework combining Floquet and Landauer-Büttiker theories to analyze nonlinear responses and harmonic generation in graphene transistors under ac drive.

Findings

Resonance promotion of higher order sidebands due to inelastic scattering.

Selective enhancement of specific harmonics by tuning doping and drive strength.

Potential use of the device for THz detection and as a frequency multiplier.

Abstract

We present results for time-dependent electron transport in a ballistic graphene field-effect transistor with an ac-driven gate. Nonlinear response to the ac drive is derived utilizing Floquet theory for scattering states in combination with Landauer-B\"uttiker theory for transport. We identify two regimes that can be useful for applications: (i) low and (ii) high doping of graphene under source and drain contacts, relative to the doping level in the graphene channel, which in an experiment can be varied by a back gate. In both regimes, inelastic scattering induced by the ac drive can excite quasi-bound states in the channel that leads to resonance promotion of higher order sidebands. Already for weak to intermediate ac drive strength, this leads to a substantial change in the direct current between source and drain. For strong ac drive with frequency $\Omega$, we compute the higher harmonics of frequencies $n\Omega$ ($n$ integer) in the source-drain conductance. In regime (ii), we show that particular harmonics (for instance $n=6$) can be selectively enhanced by tuning the doping level in the channel or by tuning the drive strength. We propose that the device operated in the weak-drive regime can be used to detect THz radiation, while in the strong-drive regime it can be used as a frequency multiplier.