Ref HAL: hal-01436892_v1
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Fabrication and experimental tests of materials and optics for Terahertz range used in field effect transistor detectors arrays are described. The method using diffractive optics, fabricated in 3D printing technology, was used for tests with GaN/AIGaN based FETs sub-THz detectors working in 300 GHz atmospheric window. The lens arrays focus energy exactly on the detectors and additionally reduce mutual detector crosstalk. Finally they improve detectors signal to noise ratio by more than one order of magnitude. Moreover such lens arrays are cost-effective, easy reproducible and thin elements.

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WoS: WOS:000390422000106
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Experimental and theoretical investigations of the influence of substrate thickness on the performance of Si field effect transistor terahertz detectors are presented.. We show that in the case of planar metal antennas a significant portion of incoming radiation, instead of being coupled to the transistors, may be coupled to the substrate leading to important responsivity losses..The ways of avoiding these losses are discussed.

Ref HAL: hal-01436847_v1
WoS: WOS:000390422000183
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We report on the photoresponse of AlGaN/GaN HEMT to THz radiation of low and high intensity. We show that the response vs. gate bias dependence can be described by the theory of Dyakonov-Shur in the whole range of radiation intensity. Unusual behavior of the photoresponse vs. intensity was observed under laser irradiation: a quadratic increase of the response followed by saturation. We speculate that this phenomenon can be explained by hot electrons capture by traps in AlGaN or buffer layers.

Ref HAL: hal-01436054_v1
WoS: WOS:000390422000134
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We present results of investigations of Plasma Assisted Molecular Beam Epitaxy (PAMBE) - grown GaN/AIGaN High Electron Mobility Transistor (HEMT) structures for fabrication of detectors and emitters operating in THz spectral range. These devices are standard HEMT structures but equipped with additional antennas that ensure THz radiation coupling. THz detectors and emitters were processed using different HEMT designs. The results of emission experiments at room temperature demonstrate emission in the spectral range from 0.5 to 12 THz with a total integrated power of the single transistor of the order of 100 nW. The results of room temperature THz detection (photoresponse experiments) in the ranges 110-170 and 220-330 GHz are presented and discussed. THz experiments, transistor electrical tests and data analysis presented in this work, clearly show that PAMBE grown GaN/AIGaN transistors can used as promising elements of future THz imaging systems.

Ref HAL: hal-01436049_v1
WoS: WOS:000390422000107
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An overview of main results concerning THz detection related to plasma nonlinearities in nanometer field effect transistors is presented. In particular nonlinearity and dynamic range of these detectors are discussed. As a conclusion, we will show one of the first real world application of the FET THz detectors: a demonstrator of the imager developed for fast postal security.

Ref HAL: hal-01426431_v1
DOI: 10.1103/PhysRevB.94.054525
WoS: WOS:000383029200005
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6 Citations
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Superconducting hybrid junctions are revealing a variety of effects. Some of them are due to the special layout of these devices, which often use a coplanar configuration with relatively large barrier channels and the possibility of hosting Pearl vortices. A Josephson junction with a quasi-ideal two-dimensional barrier has been realized by growing graphene on SiC with Al electrodes. Chemical vapor deposition offers centimeter size monolayer areas where it is possible to realize a comparative analysis of different devices with nominally the same barrier. In samples with a graphene gap below 400 nm, we have found evidence of Josephson coherence in the presence of an incipient Berezinskii-Kosterlitz-Thouless transition. When the magnetic field is cycled, a remarkable hysteretic collapse and revival of the Josephson supercurrent occurs. Similar hysteresis are found in granular systems and are usually justified within the Bean critical state model (CSM). We show that the CSM, with appropriate account for the low-dimensional geometry, can partly explain the odd features measured in these junctions.

Ref HAL: hal-01939530_v1
Ref Arxiv: 1611.08179
DOI: 10.1103/PhysRevLett.117.237702
WoS: WOS:000389032600014
Ref. & Cit.: NASA ADS
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12 Citations
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We report on the stability of the quantum Hall plateau in wide Hall bars made from a chemically gated graphene film grown on SiC. The ν=2 quantized plateau appears from fields B≃5  T and persists up to B≃80  T. At high current density, in the breakdown regime, the longitudinal resistance oscillates with a 1/B periodicity and an anomalous phase, which we relate to the presence of additional electron reservoirs. The high field experimental data suggest that these reservoirs induce a continuous increase of the carrier density up to the highest available magnetic field, thus enlarging the quantum plateaus. These in-plane inhomogeneities, in the form of high carrier density graphene pockets, modulate the quantum Hall effect breakdown and decrease the breakdown current.