Nanometer size field effect transistors can operate as efficient resonant or broadband terahertz detectors, mixers, phase shifters and frequency multipliers at frequencies far beyond their fundamental cut-off frequency. This work is an overview of some recent results concerning the application of nanometer scale field effect transistors for the detection of terahertz radiation.

The nonresonant detection of terahertz detectors based on asymmetric dual-grating-gate (A-DGG) high electron mobility transistors has been reported at both terahertz and sub-terahertz frequencies in several papers; but its behavior could not be fully understood in the range of the gate voltages close to and below the threshold voltage Vth. Two different contributions can attenuate the photoresponse u in the sub-threshold voltage region. The model developed in Ref. 3 showed that the gate leakage current suppresses the detector terahertz photoresponse in the sub-threshold region, leading to a nonresonant maximum in photoresponse versus gate dependence. While, in the model of Ref. 4, the detector loading effects were considered as responsible for the signal drop in the sub-threshold range. These effects are related to the voltage divider formed by input impedance of the measurement apparatus and the channel resistance of the detector which is exponentially increasing below threshold [4]. In the framework of the ANR-JST WITH project, we performed detailed studies of both the voltage u and the current i photoresponse of A-DGG devices. The photoresponse i was determined using the transfer characteristics measured with and without applied terahertz radiation. The measurements were carried out as a function of gate voltage and temperature (4 - 300 K), for incoming radiation frequencies of 292 and 655 GHz. As a result, we show that both effects are important and their relative contributions depend on gate voltage and temperature. We determine the separate contributions of the gate leakage current and the loading effect to the terahertz rectification signal in the sub-threshold region.

In this work, we undertake detailed studies of the mesoscopic rectification of an ac current at THz frequency induced by the incoming radiation for back-gated graphene field effect transistors. Using THz detection as a probe, we explore the nonlinear behavior of the quantum fluctuations and weak localization.

The reflection, transmission and absorbance spectra of silicon nanowire arrays (NWAs), as a function of the length of the nanowires, are investigated in a wavelength range of 15 μm < λ < 200 μm, using Fourier transform infrared spectroscopy in vacuum. The NWAs are fabricated using metal-assisted electroless chemical etching. The wire length is varied between 20 μm and 140 μm, which is of the same order of magnitude as the wavelength, and their spectra are compared to bulk Si. At high frequencies the absorbance spectra of the NWAs show molecular resonances due to adsorption of molecules involved in the fabrication process but also due to the oxide quality that wraps the nanowires and changes as a function of nanowire length. Transmission characteristics show an increasing shift in absorption band edge towards the far infrared for longer wires and a transition from specular to diffuse reflection at a nanowire length of approximately 60 μm.

Double-grating-gate field-effect transistors have a great potential as terahertz detectors. The double grating gate serves not only for carrier density tuning but also as an efficient THz radiation coupler. Low and high magnetic field detection results are used to determine the electron mobility and electron concentration, respectively, in the different parts of the channel.

The concept of THz detection based on excitation of plasma waves in two-dimensional electron gas in Si FETs is one of the most attractive ones, as it makes possible the development of the large-scale integrated devices based on a conventional microelectronic technology including on-chip antennas and readout devices integration. In this work we report on investigations of Terahertz detectors based on low-cost silicon technology field effect transistors. We show that detectors, consisting of a coupling antenna and a n-MOS field effect transistor as rectifying element, are efficient for THz detection and imaging. We demonstrate that in the atmospheric window around 300 GHz, these detectors can achieve a record noise equivalent power below 10 pW/Hz0.5 and a responsivity above 90 kV/W once integrated with on-chip amplifier. We show also that they can be used in a very wide frequency range: from ∼0.2 THz up to 1.1 THz. THz detection by Si FETs pave the way towards high sensitivity silicon technology based focal plane arrays for THz imaging

We report on a magnetospectroscopy study of a set of four HgTe quantum wells of different thickness. In quantizing magnetic fields, intraband and interband transitions have been observed. The obtained results are compared with the allowed transition energies calculated using the 8 × 8 Kane model.