Detection of terahertz radiation in graphene structure under conditions of strong spatial inhomogeneity of the plasmon electric field

Background and Objectives: Research of terahertz (THz) wave rectification in graphene shows the increase of the rectified current in p-n graphene structures relatively to graphene having only n- or p-type of conductivity. The p-n junctions in graphene may be created 144 by both a chemical or electrical doping of graphene. There were discussed several physical mechanisms for wave rectification in graphene structures, that are the photothermoelectric effect, Drude heating of carriers by THz radiation and nonlinear plasmonic effects. Methods: The detection of terahertz radiation in a spatially periodic structure with spatially inhomogeneous graphene is theoretically investigated. To create spatial asymmetry and inhomogeneity, graphene in each unit cell is screened by two metal electrodes with different widths and a uniform gate at the bottom. Due to the application of dc electrical voltages between the different gate electrodes and graphene in the unit cell of periodic graphene the areas with electron and hole conductivities are created. We solved the electromagnetic problem of plasmon excitation in the graphene structure by an incident terahertz wave, the electrostatic problem of calculating the carrier density in graphene depending on the set dc voltages at different gates, and the nonlinear hydrodynamic problem of charge carrier dynamics on calculating the rectified current induced by the plasma wave in spatially periodic graphene. Results: In such a graphene system, the dominant mechanism for detecting terahertz radiation is the plasmon electron-hole ratchet effect. It has been found that due to the effect of the plasmon electron-hole ratchet, the rectified current increases with increasing spatial inhomogeneity of the electric field of plasmon in graphene.