Resonant frequencies of the two-dimensional plasma in field effect transistors (FETs) increase with the reduction of the channel dimensions and can reach the Terahertz (THz) range. Nonlinear properties of the plasma/electron gas in the transistor channel can be used for the rectification and detection of THz radiation. The excitation of plasma waves by sub-THz and THz radiation was demonstrated for short gate transistors at cryogenic temperatures. At room temperature plasma oscillations are usually overdamped, but the FETs can still operate as efficient broadband rectifiers/detectors in the THz range. We present a few recent experimental results on THz detection by FETs showing some new ways of improvement of FETs for THz imaging at room temperature as well as the new physical phenomena like detection in quantizing magnetic fields. We also demonstrate THz emission properties of GaN based FETs.

Subwavelength antennas in the metal interconnection layer of an inexpensive CMOS chip couple terahertz radiation to the chip's electronics, enabling the creation of inexpensive, compact imagers.

Magnetotransport and magnetooptics investigations of plasmon excitations in large-area grating-gate terahertz modulators based on AlGaN/GaN high-electron-mobility transistors with different grating-gate duty cycle are reported. We demonstrate that the effect of the gate potential on the ungated region extends beyond the conventional fringing effect distance, ranging over 250-350 nm instead of expected 26-30 nm. This phenomenon enables excitation of the localized gated magnetoplasmon modes only if the inter-finger spacing in the grating gate exceeds 350 nm. For narrower slits, only the collective gated magnetoplasmon modes extending over the entire period of the structure can be excited.

We report on reflective electro-optic sampling measurements of TeraHertz emission from nanometer-gate-length InGaAs-based high electron mobility transistors. The room temperature coherent gate-voltage tunable emission is demonstrated. Our results shows that properly exciting nanotransistors can pave the way for new class of coherent and easily tunable THz sources. (C) 2010 Optical Society of America

In this work, the performance of InP-based HEMTs as a THz detector was experimentally studied. The nature of the THz rectification by the two-dimensional plasmons in which the DC drain current variation Delta I-d becomes maximal around the threshold voltage was observed. Based on the imaging measurement, it was confirmed that our HEMTs device can work for sensitive THz imaging at 0.3 THz. The directivity of the detector was characterized with the maximum responsivity of 26.1 V/W at theta = 160 degrees.

Possibilities and advantages of the electro-optical sampling (EDS) technique for the investigation of excitation of THz-range 2D plasma waves in FET/HEMT channels are considered both experimentally and theoretically. It is experimentally demonstrated that the EOS technique allows one to identify an excitation of 2D plasma waves in the HEMT channel under a given working point determined by external embedding circuits. Theoretical simulations show that the development of the instability of 2D plasma waves can be easily identified in the framework of the EOS technique.

This paper reviews recent advances in emission of terahertz radiation from two-dimensional (2D) electron systems in semiconductor nano-heterostructures. 2D plasmon resonance is first presented to demonstrate intense broadband terahertz emission from InGaP/InGaAs/GaAs and InAlAs/InGaAs/InP material systems. The device structure is based on a high-electron mobility transistor and incorporates the author's original interdigitated dual-grating gates. Second topic focuses on graphene, a monolayer carbon-atomic honeycomb lattice crystal, exhibiting unique carrier transport and optical properties owing to massless and gapless energy spectrum. Coherent stimulated terahertz emission from femtosecond infrared-laser pumped epitaxial graphene is experimentally observed, reflecting the occurrence of negative dynamic conductivity and population inversion