PERIODIC GRATING-GATE SCREENING OF PLASMONS IN HETEROJUNCTION STRUCTURES

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.