Periodic grating-gate screening of plasmons in heterojunction structures

Abstract

The far-infrared optical response of a structure consisting of a perfectly conducting grating gate on a modulation-doped GaAs/AlGaAs heterojunction has been calculated using the scattering matrix technique. The grating gate allows coupling between the incident radiation and the plasmon resonance of the two-dimensional electron gas (2DEG) in such a system, but also modifies the dispersion relation for the plasmon because of screening by the image charge distribution induced on the grating gate. Using the scattering matrix technique allows this screening effect to be modeled more accurately than has hitherto been possible, and our calculations show that the induced charge is concentrated at the edges of the grating fingers. The sinusoidal profile of the oscillating charge density in the 2DEG distorts so that the maximum amplitude of the oscillation is close to these edges, and the plasmon frequency is determined by the amount of distortion of the plasmon charge density profile and the additional screening gained through the distortion. Plasmon frequencies are calculated for a wide range of lamellar grating mark/space ratios, and are found to lie between the extremes predicted for plasmons in 2DEGs close to a vacuum interface and close to a continuous metal gate.

Transmission line theory of collective plasma excitations in periodic two-dimensional electron systems: Finite plasmonic crystals and Tamm states

“…The plasmon energy band spectrum has been found numerically in various approximations [32][33][34][35][36]. Density and field distributions in the split plasmon modes at the edges of the band gap and their interaction with incident EM field have also been analyzed [37][38][39]. Recently plasmonic band spectrum has been calculated in the gated 2DEG with periodically modulated plasma wave velocity [40].…”

Plasmon Excitation and Plasmonic Detection of Terahertz Radiation in the Grating-Gate Field-Effect-Transistor Structures

“…2) with a homogeneous (unmodulated) 2D electron channel were considered in [27][28][29]. Plasmon mode excitation in the 2D electron system with a spatially modulated electron density was studied in [30][31][32][33][34], where the plasmon modes localized in the regions of the channel with a small electron density under the grating-gate fingers were considered.…”

Radiative decay of optically excited coherent plasmons in a two-dimensional electron gas

“…For the same wave vector, the frequency of radiative modes is lower than that of nonradiative modes, which reflects the more effective screening of the plasma oscillations by the grating metallization. 16 Under oblique incidence or emission, the coupling of nonradiative modes to FIR radiation is no longer strictly forbidden. 20 Still, the coupling efficiency of the radiative modes is at least 403 stronger than that of the nonradiative modes for all the incidence or emission angles.…”

“…The effective dielectric constant e of the radiative modes can be approximated for large values of r by an expression derived for fully metallized surfaces. In this so-called covered-surface limit, e is given by 16,21 e e 2 1 e 1 coth͑k k D͒ 2 .…”