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

Artikel i vetenskaplig tidskrift, 2016

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-Buttiker 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 quasibound 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.