High-modulation system based on graphene-structured Schottky junction for terahertz signal transmission

Abstract

In recent years many technological applications based on graphene-structured systems have attracted great interest of the solid state community due to the non-peculiar optical properties of graphene related to the strong movility of the charge carriers of this material. One of these applications is the electro-optical modulator, which becomes a key device for optical communication. In this connection, in this paper we theoretically propose an electro-optical system based on a graphene-structured Schottky junction and gated by a low voltage, which induces a considerably transmission modulation of the terahertz signal. One of the most important results of the presented system, that is supported on the strong interaction between Dirac electrons and circularly polarized photons of the field radiation, lies especially in that no extra pumping optical field is needed to obtain a modulation depth around 97% for a low gate voltage of 0.42 V. For positive voltages, the signal amplitude strongly increases till the built-in potential value is reached. For voltage values over the built-in potential a reversing tendency of the modulation depth is observed, whereas for negative values of the voltage the modulation decreases, presenting the system a classical Schottky diode behavior. We also report an oscillatory behavior of the signal amplitude that, in addition to the known Drude behavior, complements the description of the terahertz transmission spectra. In this context, we develop a quantum formulation, which is able to describe clearly these nonlinear effects on the basis of the coherent and incoherent momentum relaxation of photon-dressed electrons at impurities in such graphene-structured systems.