The current flowing in two-dimensional channel of field effect transistors can generate different types of charge density perturbations. They can have a form of uncorrelated hot plasmons or plasma waves. The mechanism of plasma wave generation depends on the parameter omega t and on boundary conditions of the channel. At omega t << 1 only hot plasmons can be generated. The THz emission due to radiative decay of hot plasmons has a broad spectrum and can be only poorly controlled by the transistor gate. The tunability of THz emission can be obtained in the case of the Dyakonov-Shur plasma wave instability. In this work we present experimental studies of THz emission in InGaP/InGaAs/GaAs and GaN/AlGaN based field effect transistors. We report on two types of emission onset: (i) a smooth one typical for hot plasmons generation and (ii) threshold-like one characteristic for plasma waves instabilities. The tunability and spectra of emission change depending on the transistor configuration. We discuss the results suggesting several possible mechanisms of plasma wave excitation.

We report on the resonant detection of a 3.1 THz radiation produced by a quantum cascade laser using a 250 nm gate length GaAs/AlGaAs field effect transistor at liquid nitrogen temperature. We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel. The detection is enhanced by increasing the drain current and driving the transistor into saturation regime. These results clearly show that plasma wave nanometer-size transistors can be used as detectors in all-solid-state terahertz systems where quantum cascade lasers act as sources.

Recent advances in materials and device structures for terahertz imaging and sensing technology are reviewed. The fundamental physical principle for terahertz imaging/sensing is focused on the nonlinear dynamics of plasmons in two-dimensional semiconductors including quantum wells in III-V based heterostructures as well as graphene.

We report on nonresonant detection of terahertz radiation using our original InGaP/InGaAs/GaAs plasmonresonant high-electron-mobility transistor having a dual grating gate (DGG) structure. The experiments were performed at room temperature using a Gunn diode operating at 0.30 THz as the THz source. Using a deviceloading model, the intrinsic responsivity was extracted and was dependent on the polarization of the incident THz wave. The device exhibited highest response when the electric-field vector of the incident THz radiation was directed in the source-drain direction. The 2D spatial distribution image of the transistor responsivity shows a clear beam focus centred on the transistor position, which proves the appropriate coupling of the THz radiation to the device, due to the DGG structure. The device also showed a high intrinsic responsivity of similar to 90 V/W and a noise equivalent power (NEP) as low as similar to 10-10 WHz(-0.5). (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Plasmonic terahertz detection by a double-grating gate field-effect transistor structure with an asymmetric unit cell is studied theoretically. Detection responsivity exceeding 8 kV/W at room temperature in the photovoltaic response mode is predicted for strong asymmetry of the structure unit cell. This value of the responsivity is an order of magnitude greater than reported previously for the other types of uncooled plasmonic terahertz detectors. Such enormous responsivity can be obtained without using any supplementary antenna elements because the double-grating gate acts as an aerial matched antenna that effectively couples the incoming terahertz radiation to plasma oscillations in the structure channel. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3670321]

This paper investigates terahertz detectors fabricated in a low-cost 130 nm silicon CMOS technology. We show that the detectors consisting of a nMOS field effect transistor as rectifying element and an integrated bow-tie coupling antenna achieve a record responsivity above 5 kV/W and a noise equivalent power below 10 pW/Hz(0.5) in the important atmospheric window around 300 GHz and at room temperature. We demonstrate furthermore that the same detectors are efficient for imaging in a very wide frequency range from similar to 0.27 THz up to 1.05 THz. These results pave the way towards high sensitivity focal plane arrays in silicon for terahertz imaging. (C) 2011 Optical Society of America

In this work we review the most important results concerning the physics and applications of FETs as Terahertz detectors [1]. We present two experiments showing: i) Terahertz detection based on low cost 130 nm silicon technology Field Effect Transistors in the sub-THz range (0.2 THz up to 1.1 THz) and ii) first results on detection by FETs of emission from 3.1 THz Quantum Cascade Lasers.