The channel of nanometre field effect transistor can act as a resonant cavity for plasma waves. The frequency of these plasma waves is in the Terahertz range and can be tuned by the gate length and the gate bias. During the last few years Terahertz detection and emission related to plasma wave instabilities in nanometre size field effect transistors was demonstrated experimentally. In this work we review the recent results on sub-THz and THz detection by 50-300nm gate length III-V HEMTs and Si MOSFETs. We present experimental results on the resonant and nonresonant (overdamped) plasma wave detection and discuss possible applications of nanometre field effect transistors as new detectors of THz radiations.

We report on resonant terahertz detection by the two-dimensional electron plasma in nanometric InGaAs and GaN transistors. Up to now, the majority of research has been devoted to GaAs-based devices as the most promising from the point of view of the electron mobility. However, resonant detection has been reported only in the sub-THz range. According to the predictions of the Dyakonov–Shur plasma wave detection theory, an increase of the detection frequency can be achieved by reducing the length or increasing the carrier density in the gated region. We demonstrate that the 1 THz limit can be overcome by using ultimately short-gate InGaAs and GaN nanotransistors. For the first time the tunability of the resonant signal by the applied gate voltage is demonstrated. We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel (Dyakonov–Shur theory). We also show that increasing of the drain-to-source current leads to a transformation of the broadband detection to a resonant and tuneable one. We can get resonant detection at room temperature. We finally discuss the possible application of detection by nanotransistors in different types of THz spectroscopy research.

Si metal oxide semiconductor field effect transistors (MOSFETs) with the gate lengths of 120-300 nm have been studied as room temperature plasma wave detectors of 0.7 THz electromagnetic radiation. In agreement with the plasma wave detection theory, the response was found to depend on the gate length and the gate bias. The obtained values of responsivity (<= 200 V/W) and noise equivalent power (>= 10(-10) W/Hz(0.5)) demonstrate the potential of Si MOSFETs as sensitive detectors of terahertz radiation. (c) 2006 American Institute of Physics.

Plasma oscillations in nanometer field effect transistors are used for detection and generation of electromagnetic radiation of THz frequency. Following first observations of resonant detection in 150 nm gate length GaAs HEMT, we describe recent observations of room temperature detection in nanometer Si MOSFETs, resonant detection in GaN/AlGaN HEMTs and improvement of room temperature detection in GaAs HEMTs due to the drain current. Experiments on spectrally resolved THz emission are described that involve room and liquid helium temperature emission from nanometer GaInAs and GaN HEMTs.

Detection of subterahertz and terahertz radiation by high electron mobility GaN/AlGaN transistors in the 0.2-2.5 THz frequency range (much higher than the cutoff frequency of the transistors) is reported. Experiments were performed in the temperature range 4-300 K For the lowest temperatures, a resonant response was observed. The resonances were interpreted as plasma wave excitations in gated two-dimensional electron gas. Non-resonant detection was observed at temperatures above 100 K. Estimates for noise equivalent power show that these transistors can be used as efficient detectors of terahertz radiation at cryogenic and room temperatures.

We present theoretical and experimental studies of the direct current effect on the detection of subterahertz and terahertz radiation in gated two-dimensional structures. We developed a theory of the current-driven detection both for resonant case, when the fundamental frequency of plasma oscillation is large compared to inverse scattering time, omega(0)tau >> 1, and for the nonresonant case, omega(0)tau << 1, when the plasma oscillations are damped. We predict that, in the nonresonant case, even a very small dc current would increase the detection amplitude up to two orders of magnitude. Physically, this increase is related to an abrupt transition from the linear to saturation region near the knee of the current-voltage characteristic. When the current increases up to the saturation value, the electron concentration near the drain becomes very low and can be strongly affected by a small external field. As a consequence, the two-dimensional channel becomes extremely sensitive to external perturbations. In the resonant case, the detection amplitude has maxima when the radiation frequency is equal to fundamental plasma frequency and its harmonics. We predict that the effective linewidths of the respective resonances would decrease with the increasing current. Physically, this happens because dc current shifts the system towards the plasma wave instability. At some critical current value, the width corresponding to the fundamental frequency would turn to zero, indicating the onset of plasma waves generation. Our experimental measurements performed on GaAs HEMT confirm the theoretical predictions.