Plasmonic instabilities in two-dimensional electron channels of variable width

Abstract

Understanding of fundamental physics of plasmonic instabilities is the key issue for the design of a new generation of compact terahertz electronic sources required for numerous THz applications. Variable width plasmonic devices have emerged as potential candidates for such an application. The analysis of the variable width plasmonic devices presented in this paper shows that these structures enable both the Dyakonov-Shur instability (when the electron drift velocity everywhere in the device remains smaller than the plasma velocity) and the "plasmonic boom" instability that requires drift velocity exceeding the plasma velocity in some of the device sections. For symmetrical structures, the driving current could be provided by an RF signal leading to RF to Terahertz (THz) and THz to RF frequency conversion using the source and drain antennas and reducing losses associated with ohmic contacts. We show that narrow regions protruding from the channel ("plasmonic stubs") could control and optimize boundary conditions at the contacts and/or at the interfaces between different device sections. These sections could be combined into plasmonic crystals yielding enhanced power and a better impedance matching. The mathematics of the problems is treated using the transmission line analogy. We show that the combination of the stubs and the variable width channels is required for the instability rise in an optimized plasmonic crystal. Our estimates show that THz plasmonic crystal oscillators could operate at room temperature.

Terahertz Plasmonic Technology

“…This approach allows for the accurate compact modeling of TeraFETs using ADS or SPICE. [112] Table II (from [114]) shows the estimated values of Qm and f p for Si, GaN, InGaAs, and p-diamond TeraFETs at 300 and 77 K. The gate swing was chosen to maximize the quality factor. As seen, a resonant detection ( 1 m Q >> ) is possible even at room temperature even though non-resonant detection is much easier to achieve.…”

“…The attempts to increase the responsivity involve using the ratchet effect [121][122][123][124][125][126], grated gate structures [105][106][107], [127][128][129][130][131], plasmonic boom [132,133], and variable width devices [114]. We call such structures plasmonic crystals with the unit cells smaller or comparable to the mean free path but capable of capturing and processing a larger THz flux.…”

“…The values of Qm and fm for Si, GaN, InGaAs, and p-diamond TeraFETs at 300 and 77 K. The gate swing is chosen to maximize the quality factor. (From[114) …”

Scattering-induced amplification of two-dimensional plasmons: Electromagnetic modeling

“…Different types of instabilities have been investigated, but the common idea is to use discontinuities in 2D channels to realize plasmon amplification in the presence of a dc current, and to use reflections from the discontinuities to provide feedback needed for oscillations. Such discontinuities can be realized by electric contacts 32,33,47,55 , by interfaces between gated and ungated channels 42,44,53 , or by a variation in the channel geometry 36,41,43,56 . However, physical interpretation of the effects may differ depending on the approach chosen.…”

“…[11,[37][38][39]); evidence of plasmon amplification from interface scattering has come to date from observing radiation from double-gratinggate transistors 40 . Several theoretical studies [41][42][43] concentrated on analytical models for the plasmon transmission and reflection coefficients. A typical approximation is to reduce the three-dimensional interface to a single line of contact between two-dimensional systems.…”