Abstract— We observed, for the first time, resonant absorption and modulation of THz radiation by 2DEG plasmons in GaN- based large area grating-gate structures. Transmission spectra of the fabricated grating-gate devices were measured by a commercial FTIR system using a blackbody emitter as broadband radiation source and a CW FIR gas laser. Obtained spectra clearly showed the absorption peaks, which were attributed to the resonance plasmon excitation in the 2DEG at the AlGaN/GaN heterointerface. The results demonstrate the potential of using GaN-based plasmonic device for THz applications. Index Terms—Terahertz, detectors, modulators, Gallium nitride I. INTRODUCTION T Hz radiation has found many applications for sensing and characterization of chemical and biological systems and for detection of concealed weapons and explosives. Such applications require detectors possessing high responsivity, sensitivity, fast response and operation at room temperature. THz detectors based on plasma waves in FETs have demonstrated fast response time and comparable sensitivity with conventional detection methods [1-3]. Such FETs support two different types of plasma oscillations. The first is the plasma oscillations in the gated region of the 2DEG channel. If an infinite perfectly conductive plane is located at distance d The work of N. Pala was supported by ARO under SBIR and work of D. Veksler was supported by the NSF (Grant No. 0333314)) and by the NSF Connection One I/UCRC at RPI. This work was performed in part at the Cornell NanoScale Facility, a member of the National Nanotechnology Infrastructure Network, which is supported by the National Science Foundation (Grant ECS 03-35765). N. Pala and R. Gaska are with Sensor Electronic Technology, Inc. Columbia, SC 29209 USA (e-mail: palan@ s-et.com). N. Pala is also with ECSE Department and CIE, Rensselaer Polytechnic Institute, Troy, NY 12208 USA. W. Stillman, and M. S. Shur are with ECSE Department and CIE, Rensselaer Polytechnic Institute, Troy, NY 12208 USA. M. S. Shur is also with Physics Department, Rensselaer Polytechnic Institute, Troy, NY 12208 USA. D. Veksler, A. Muravjov are with Physics Department, Rensselaer Polytechnic Institute, Troy, NY 12208 USA. from the infinite 2D electron sheet, and the conducting plane is close enough to 2D electron sheet (i.e. kd<<1) then the dispersion relation is given by [4] k m Nd e p 1 0 * 2 ε ε ω = (1) where ω p and k are the frequency and wave vector of plasma wave, respectively, N is the sheet electron density, e and m* are the charge and effective mass of electron, ε 0 is the dielectric permittivity ε 1 is the dielectric constant of the insulator separating the 2D electron layer from the perfectly conductive plane. Eq. 1 indicates that plasma waves in the gated region have frequency independent phase velocity s=ω/k. The second type of plasma oscillations exist in ungated regions. For negligible electron scattering in 2D electron gas, the dispersion relation for ungated plasma oscillations in an infinite homogenous 2D electron sheet is k m N e p ε ε ω 0 * 2 2 = (2) where ε is the effective dielectric function which depends on the geometry of the structure. However, response of a single FET plasma detector is limited by its small area compared to the beam cross section. Also, gated plasmons in a single-gate FET are weakly coupled to terahertz radiation because of the strong screening of the gate plasmons by the metal gate electrode and their Resonant Detection and Modulation of Terahertz Radiation by 2DEG Plasmons in GaN Grating-Gate Structures Nezih Pala, Member IEEE, Dmitry Veksler, Andrey Muravjov, William Stillman, Remis Gaska, M. S. Shur, Fellow IEEE w L N 2 N 1 2D channel grating gate barrier THz radiation substrate E 0 source drain Fig. 1. Schematics of the GaN-based large area grating-gate devices with 2DEG plasmons