Analytical and numerical studies of the dispersion properties of grating gated THz plasmonic structures show that
the plasmonic crystal dispersion relation can be represented in terms of effective index of the dielectric medium
around the 2DEG for the plasmons. Forbidden energy band gaps are observed at Brillion zone boundaries of the
plasmonic crystal. FDTD calculations predict the existence of the plasmonic modes with symmetrical, antisymmetrical
and asymmetrical charge distributions. Breaking the translational symmetry of the crystal lattice by
changing the electron concentration of the two dimensional electron gas (2DEG) under a single gate line in every 9th gate induces a cavity state. The induced cavity state supports a weekly-coupled cavity mode.
The device applications of plasmonic systems such as graphene and two dimensional electron gases (2DEGs) in III-V
heterostructures include terahertz detectors, mixers, oscillators and modulators. These two dimensional (2D) plasmonic
systems are not only well-suited for device integration, but also enable the broad tunability of underdamped plasma
excitations via an applied electric field. We present demonstrations of the coherent coupling of multiple voltage tuned
GaAs/AlGaAs 2D plasmonic resonators under terahertz irradiation. By utilizing a plasmonic homodyne mixing
mechanism to downconvert the near field of plasma waves to a DC signal, we directly detect the spectrum of coupled
plasmonic micro-resonator structures at cryogenic temperatures. The 2DEG in the studied devices can be interpreted as
a plasmonic waveguide where multiple gate terminals control the 2DEG kinetic inductance. When the gate tuning of the
2DEG is spatially periodic, a one-dimensional finite plasmonic crystal forms. This results in a subwavelength structure,
much like a metamaterial element, that nonetheless Bragg scatters plasma waves from a repeated crystal unit cell. A
50% in situ tuning of the plasmonic crystal band edges is observed. By introducing gate-controlled defects or simply
terminating the lattice, localized states arise in the plasmonic crystal. Inherent asymmetries at the finite crystal
boundaries produce an induced transparency-like phenomenon due to the coupling of defect modes and crystal surface
states known as Tamm states. The demonstrated active control of coupled plasmonic resonators opens previously
unexplored avenues for sensitive direct and heterodyne THz detection, planar metamaterials, and slow-light devices.
The two-dimensional plasma resonance excited in the channel of a field effect transistor has recently been utilized as
the frequency-selective absorber in a monolithic far infrared plasmonic cavity detector. In this article we discuss the
relevant parameters pertaining to engineering the plasmonic cavity and an integrated detection element as
constituent elements of a resonant far infrared detector. The spectra of low-order plasmon modes in 18 μm and 34
μm long two-dimensional plasmonic cavities with 4 μm period grating gates have been measured. When the length
of the plasma cavity is significantly larger than the gate length or period, the cavity length rather than grating period
defines the plasmon wavevector. Electronic noise sources are considered; random telegraph noise is suggested as a
dominant noise source when the device is operated as a highly resistive bolometric detector.
Voltage-tunable plasmon resonances in a InGaAs/InP high electron mobility transistor (HEMT) are reported. The gate
contact consisted of a 0.5 micron period metal grating formed by electron-beam lithography. Narrow-band resonant
absorption of THz radiation was observed in transmission in the range 10 - 50 cm<sup>-1</sup>. The resonance frequency red-shifts
with increasing negative gate bias as expected. Photo-response to a tunable far-IR laser is reported. The device may
have application in high-frame-rate THz array detectors for spectral imaging with real-time chemical analysis.
We have fabricated and characterized plasmonic terahertz detectors that integrate a voltage controlled planar barrier with
a grating gated GaAs/AlGaAs high electron mobility transistor. These detectors exhibit a narrowband, tunable
plasmonic response. Substantially increased responsivity is achieved by introducing an independently biased, narrow
gate that produces a lateral potential barrier adjacent to the drain when biased to pinch-off. DC electrical characterization
in conjunction with bias-dependent terahertz responsivity and time constant measurements indicate that a hot electron
bolometric effect is the dominant response mechanism over a broad range of experimental conditions. The temperature
dependence of the bolometric response is consistent with the energy relaxation time and absorption coefficient of a
2DEG. Rectification resulting from non-linear current-voltage characteristics also appears to contribute to the response.
Additionally, we have begun investigating the operation of this device with the full grating gate biased to pinch-off to
produce many detection elements in series.