Terahertz plasma waves velocity control in a metal-semiconductor wedge waveguide with diffusively-pumped graphene

Velocity control and deceleration of terahertz plasma waves (plasmons) in the metal-semiconductor wedge waveguide with diffusion-pumped graphene is theoretically studied. We show the possibility of tuning the velocity of plasmons via diffusion pumping of graphene from the wedged semiconductor. The velocity of the plasmons in the wedge waveguide inlet terminal can be fully matched to the velocity of the rapid enough (with the velocities of about 0.07 of the speed of light) terahertz plasmons which can be excited in vicinity of the inlet terminal of the wedge waveguide by a dielectric prism with relatively low optical density in the attenuated total reflection regime. It was shown that rapid terahertz plasmon excited in the inlet terminal can be efficiently slowed down while moving toward the wedge apex (the plasmon phase velocity becomes almost an order of magnitude smaller near the outlet terminal of the wedge waveguide compared its value in the inlet terminal). The deceleration of terahertz plasmon is caused by two factors: first, increasing of screening of the plasma wave near the wedge apex by the metal and, secondly, decreasing the plasmon velocity due to the gradient of free carrier concentration in graphene realized by graphene pumping in the wedge structure. The studied control of terahertz plasmons is in demand for better manipulation of these waves, enabling the design of THz modulators, phase shifters, sensors etc.