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. We establish that the physical mechanism of the coherent terahertz emission is related to the plasma waves driven by simultaneous current and optical excitation. A significant shift of the plasma frequency and the narrowing of the emission with increasing channel's current are observed and explained as due to the increase in the carriers' density and drift velocity.

We demonstrate that a proper antenna and transistor design can provide high responsivity for Terahertz radiation and imaging capability even above the 1 THz limit with a low-cost 130 nm CMOS technology. This result opens the way to CMOS THz imagers working at high frequencies and therefore exhibiting high a spatial resolution - down to similar to 300 mu m.

GaAs field effect-transistors are used for single-pixel imaging using frequencies above 1 THz at 300 K. Images obtained in transmission mode at 1.63 THz are recorded with spatial resolution of 300 mu m. We demonstrate that, with applied drain to source current, the imaging at up to 2.5 THz is possible.

Key components of systems operating at high millimeter wave and sub-millimeter wave/terahertz frequencies, a 140-GHz fundamental mode voltage controlled oscillator (VCO) in 90-nm CMOS, a 410-GHz push-push VCO with an on-chip patch antenna in 45-nm CMOS, and a 125-GHz Schottky diode frequency doubler, a 50-GHz phase-locked loop with a frequency doubled output at 100 GHz, a 180-GHz Schottky diode detector and a 700-GHz plasma wave detector in 130-nm CMOS are demonstrated. Based on these, and the performance trends of nMOS transistors and Schottky diodes fabricated in CMOS, paths to terahertz CMOS circuits and systems including key challenges that must be addressed are suggested. The terahertz CMOS is a new opportunity for the silicon integrated circuits community.

Resonant frequencies of the two-dimensional plasma in FETs reach the THz range for nanometer transistor channels. Non-linear properties of the electron plasma are responsible for detection of THz radiation with FETs. Resonant excitation of plasma waves with sub-THz and THz radiation was demonstrated for short gate transistors at cryogenic temperatures. At room temperature, plasma oscillations are usually over-damped, but the FETs can still operate as efficient broadband THz detectors. The paper presents the main theoretical and experimental results on detection with FETs stressing their possible THz imaging applications. We discuss advantages and disadvantages of application of III-V GaAs and GaN HEMTs and silicon MOSFETs.

Room temperature photovoltaic non-resonant detection by large area double-grating-gate InGaP/InGaAs/GaAs heterostructures was investigated in sub-THz range (0.24 THz). Semi-quantitative estimation of the characteristic detection length combined with self-consistent calculations of the electric fields excited in the structure by incoming terahertz radiation allowed us to interpret quantitatively the results and conclude that this detection takes place mainly in the regions of strong oscillating electric field excited in depleted portions of the channel.

SiGe-based bolometers originally designed for infrared operation have been tested as detectors of terahertz radiation. The obtained values of the responsivity and noise equivalent power show that these detectors can compete with conventional room temperature detectors such as pyroelectric detectors and Golay cells having an advantage in their compatibility with the CMOS technology.