We report on resonant and non-resonant (broad-band) detection of terahertz (THz) radiation using Strained-Si MODFETs. The devices were excited at room temperature by two types of THz sources at 0.292 THz and at 1.5 THz. Non-resonant response with maxima around the threshold voltage was observed. Shubnikov-de Haas along with photoresponse measurements were performed simultaneously to demonstrate that the observed response is related to the plasma waves oscillation in the channel. The device was cooled down to 4.2 K and resonant signature could be observed.

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.

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.

We report on Terahertz wireless communications and fast imaging experiments at 300 GHz, using nanometer-sized transistors as detectors. The physical mechanism of the detection is related to the overdamped plasma waves in the transistor channel.

Development of new terahertz (THz) sensors is increasing in interest due to their potential for THz imaging and spectroscopy. One alternative to develop direct THz sensors is based in the oscillation of the plasma waves in the channel of sub-micron FETs.The n-channel Si/SiGe MODFETs used in this study were grown by MBE on a thick relaxed SiGe virtual substrate grown by low-energy PECVD on plain Si wafers.

Test chips with Si MOSFETs integrating bow tie antennas are investigated to check the polarization and frequency dependence of THz sensitivity. The azimuthal angle corresponding to the maximum sensitivity changes with the pixel position on the chip. This means that the surrounding pixels affect the bow tie radiation pattern and possibly contribute to the antenna coupling. The frequency dependence suggests the presence of surface modes phenomena in the silicon substrate.