Because of their competitive Noise Equivalent Power (NEP) at room temperature and their fast modulation frequency, Field Effect Transistors (FETs) are one of the most promising devices for room temperature multipixel THz detection and imaging. We report here on an experimental study of the sub-THz detection as a function of the gate length in Silicon FETs and discuss the physical basis of their optimisation.

We observed a photovoltaic non-resonant terahertz photoresponse in a InGaAs/GaAs heterostructure with a large area double-grating-gate at room temperature. Semi-quantitative estimation of the characteristic detection length combined with self-consistent calculations of the electric fields exited in the structure by incoming terahertz radiation allowed us to interpret this detection as coming from the depleted regions of the channel.

Two experiments demonstrate that high electron mobility transistors (HEMTs) are well suited for terahertz (THz) imaging. We have shown that HEMTs can be effectively used as plasma wave detectors in a THz imaging system at frequencies higher than 1 THz at room temperature and this device are sensitive to the polarization direction of THz radiation.

The experiments on radiation coupling to field effect transistors working as terahertz radiation detectors are reported. Two types of high electron mobility transistors: InGaAs/InAlAs and GaAs/AlGaAs, with different layout geometries are studied. We show that terahertz radiation coupling efficiency is related to the layout of contact electrodes that play a role of an antenna. Our results show that the antenna coupling efficiency is one of the most important parameter to optimize in future field effect transistor based terahertz detectors.

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 for micrometer and sub-micrometer channel lengths. Non linearity of the gated electron gas in the transistor channel can be used for the detection of THz radiation. The possibility of tuneable narrow band detection in sub-THz and THz range, related to plasma resonances, has been demonstrated for nanometre gate length transistors at cryogenic temperatures. At room temperatures the plasma oscillations are usually strongly damped, but field effect transistors can still operate as an efficient broadband detectors in the THz range. We present an overview of experimental results on THz detection by field effect transistors made of III-V and Si materials, The material issue is discussed and first room applications of FETs for imaging at frequencies above 1 THz are demonstrated.

Resonance detection of terahertz radiation by submicrometer field-effect GaAs/AlGaAs transistors (with the gate length L = 250 nm) with two-dimensional electron gas in the channel has been studied at T = 4.2 K. For these transistors, it is shown for the first time that the maximum of the response (the drain-source photovoltage) shifts with an increasing frequency to the region of higher gate voltages in accordance with the Dyakonov-Shur theory. It is shown that, as temperature is increased to 77 K, the dependence of the photovoltage on the gate voltage becomes nonresonant, which is caused by a decrease in the mobility.

The possibility of using commercial classical near-infrared (similar to 30 THz) focal-plane micro-bolometer arrays in the sub-terahertz frequency range is studied. Real-time room-temperature pixilated detector imaging of a 0.5 THz (lambda = 600 mu m) spatial beam pro. le emitted from a backward-wave oscillator is presented. Images, with a signal-to-noise ratio of 5 are demonstrated, leading to an estimate of the noise equivalent power of 11 nW . Hz(-1/2).