We report on sub-Terahertz photoconductivity of bulk HgxCd1-xTe crystals withcomposition close to semiconductor-to-semimetal topological transition. Low magnetic fieldShubnikov-de Hass like oscillations were observed with a period which does not depend onthe incident frequency. Moreover, anomalous B-periodic oscillations were also observed athigher magnetic fields.

Terahertz power dependence of the photoresponse of field effect transistors, operating at frequencies from 0.1 to 3 THz for incident radiation power density up to 100 kW/cm2 was studied InGaAs high electron mobility transistors. The observed signal saturation behavior is explained by analogy with current saturation in standard direct currents output characteristics. The theoretical model of terahertz field effect transistor photoresponse was developed shows a good description match with experimental data. Our experimental results show that dynamic range of field effect transistors based terahertz detectors is very high and can extend from mW/cm2 up to kW/cm2.

The channel of the field effect transistor can operate as a cavity for plasma waves. For the electrons with high enough mobility, the plasma waves can propagate in field effect transistors (FETs) channel leading to resonant Terahertz (THz) emission or detection. In the low mobility case, plasma oscillations are overdamped, but a plasma density perturbation can be induced by incoming THz radiation. This perturbation can lead to efficient broadband THz detection. We present an overview of the main experimental results concerning the plasma oscillations in field effect transistors for the generation and the detection of terahertz radiations.

We report on the demonstration of Terahertz (THz) broadband detectors based on field effect transistors exploiting tapered semiconductor nanowires. The intrinsic asymmetry provided by the nanowires geometry allows to achieve responsivity values as high as 55 V/W (2.5 mA/W) and a noise-equivalent-power of 3 × 10−10 W/Hz1/2 independent of the specific gate voltage applied. The possibility to reduce the number of terminals required to the source and drain contacts only and the technological feasibility of multi-pixel arrays are promising for the realization of compact and integrated THz matrix array detection systems.

Interest in terahertz (THz) systems and technology has grown significantly over the past 10 years for their potential in non-invasive imaging, sensing and high-data-rate wireless communication. Waves at THz frequencies present an alternative to x-rays for imaging through paper, cloth, wood, concrete, plastic and many other materials. In contrast to x-rays they are non-ionizing and therefore inherently safe. Applications of THz radiations range from nondestructive testing to medical imaging, security screening of objects and persons. Several groups have also considered using THz waves to transmit data in wireless communications. Wireless THz communications for which THz waves are the free-space carrier of data are recognized as the promising breakthrough solution to achieve data-rates up to 100 Gbps. THz imaging and wireless communication applications suffer, however, from the lack of fast and low-cost detectors operating at room temperature and in this work we show that graphene based plasma nanotransistors can be a good alternative. .Nanotransistors offer great prospect for the development of innovative THz detectors. The interest in using field-effect transistors for THz applications was initiated by the theoretical work of Dyakonov and Shur, who predicted that the nonlinear properties of the 2D plasma in the transistor channel can be used for detection of THz waves at frequencies significantly higher than the transistor cut-off frequency. Graphene field-effect nanotransistors were recently demonstrated showing maturity of graphene microelectronics. In this paper, we present extensive studies on first THz detectors based on monolayer and bilayer graphene field effect transistors. The specific detection sign reversal related to the graphene Dirac point change of electron to hole conductivity is clearly demonstrated. We show that the detectors consisting of a gated 2D massless fermion gas as rectifying element and an integrated coupling antenna achieve a responsivity above 1.2 V/W (1.3 mA/W) in photovoltage and photocurrent mode respectively, and a noise equivalent power below 2 10-9 W/Hz0.5 We show also that these detectors can operating as sensitive room-temperature broadband THz detectors in THz imaging systems. Feasibility of THz food industry quality control and agriculture watering control imagers using graphene nanotransitor sensors/detectors is demonstrated.

We report on the development of a novel class of nanowire-based THz detectors in which the field effect transistor (FET) is integrated in a narrow-band antenna. When the THz field is applied between the gate and the source terminals of the FET, a constant source-to-drain photovoltage appears as a result of the non-linear transfer characteristic of the transistor. In order to achieve attoFarad-order capacitance we fabricate lateral gate FET with gate widths smaller than 100 nm. Our devices show a maximum responsivity of 110 V/W without amplification, with noise equivalent power levels <= 1 nW/root Hz at room temperature. The 0.3 THz resonant antenna has bandwidth of similar to 10 GHz and opens a path to novel applications of our technology including metrology, spectroscopy, homeland security, biomedical and pharmaceutical applications. Moreover the possibility to extend this approach to relatively large multi-pixel arrays coupled with THz sources makes it highly appealing for a future generation of THz detectors.

We report on room-temperature plasmonic detection of sub-terahertz radiation by InAlAs/InGaAs/InP high electron mobility transistors with an asymmetric dual-grating-gate structure. Maximum responsivities of 22.7 kV/W at 200 GHz and 21.5 kV/W at 292 GHz were achieved under unbiased drain-to-source condition. The minimum noise equivalent power was estimated to be 0.48 pW/Hz0.5 at 200 GHz at room temperature, which is the record-breaking value ever reported for plasmonic THz detectors. Frequency dependence of the responsivity in the frequency range of 0.2-2 THz is in good agreement with the theory.