Resonant excitation of plasma oscillations in a partially gated two-dimensional electron layer

Abstract

We have solved the problem of diffraction of terahertz radiation on a perfectly conductive gate strip that partially screens a two-dimensional (2D) electron layer located at some distance from the gate. Scattering and absorption spectra of such a structure reveal the fundamental plasma resonance excited under the gate. We have shown that the absorption enhancement factor at plasma resonance may reach very high values (up to 60). However, for narrow gate strips (with the width less than 100nm) the resonant scattering length of such a scatterer is shorter than its resonant absorption length by four orders of magnitude, which means that the gated plasmons in this case weakly couple to the terahertz radiation. We discuss the effects of interaction between plasma oscillations in gated and ungated regions of 2D electron layer and provide a qualitative explanation of the rather intensive terahertz emission from unstable gated plasmons in a 60-nm gate field-effect transistor observed recently.

Inducing an Incipient Terahertz Finite Plasmonic Crystal in Coupled Two Dimensional Plasmonic Cavities

“…Two dimensional (2D) THz plasmons in silicon (Si) [4], III-V materials such as GaAs/AlGaAs [5] and GaN/AlGaN [6] heterostructures, and graphene [7,8] similarly are sub-wavelength compared to free-space electromagnetic waves, but have an additional degree of freedom due to the ability to control electron density, and thus the 2D plasma frequency, through a field effect. It is this latter capability that has generated interest in 2D plasmonic devices [9,10] such as THz detectors [11][12][13][14], mixers [15,16], emitters [17,18], and field enhancement structures [19].…”

Field effect transistors for terahertz detection - silicon versus III–V material issue

“…Two main hypotheses on the origin of an additional broadening are currently under consideration: l existence of oblique plasma modes [19,20], l additional damping due to the leakage of gated plasmons to ungated parts of the transistor channel [21]. The first hypothesis is related to the fact that in realistic devices the gate width is much greater than the gate length.…”

“…Therefore, the plasma under the gate cannot be treated independently of the plasma in ungated parts. An interaction between the two plasma regions can lead not only to a modification of the resonant frequency [19,21], but also to line broadening. To decrease the role of oblique modes, one has to change the geometry of the channel.…”

“…The spectrum of plasma waves in this case is continuous, with a low frequency cut−off at the resonant plasma frequencies. The second hy− pothesis, considers a leakage of gated plasmons to ungated parts of the channel [21] It is related to the observation that normally the gate covers only a small part of the source− −drain distance. Therefore, the plasma under the gate cannot be treated independently of the plasma in ungated parts.…”

Charge density and plasmon modes in a triangular quantum well model for doped and undoped gated AlGaN/GaN HEMTs

“…The coupling mechanism between 2D plasmons and external electromagnetic waves were discussed in [4][5][6][7]. It was suggested that this coupling might be stronger using the design of field effect transistors array with grating gates [8].…”