Ref HAL: hal-03037689_v1
DOI: 10.1109/IRMMW-THz.2018.8510039
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We report on the temperature-dependent magneto absorption and magnetotransport spectroscopy of HgTe/CdHgTe quantum wells above the critical well thickness d(c). Our results, obtained in magnetic fields up to 16 T and temperature range from 1.7 to 150 K, clearly indicate a change in the band-gap energy with temperature. A topological phase transition between quantum spin Hall and trivial insulator states, revealing appearance of single-valley Dirac fermions at T = 27 and 90 K for 6.5 and 8 nm QWs respectively, was clearly observed in our magnetospectroscopy measurements.

Commentaires: 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Nagoya, JAPAN, SEP 09-14, 2018

Ref HAL: hal-01924169_v1
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Nowadays high frequency electronics uses two distinct families of semiconductors-based transistors: field effect transistors and heterojunction bipolar transistors (HBTs). They compete reaching impressive cut off frequencies going up to THz range. Except their usual functions related to switching and amplifying of current or voltage both have been demonstrated as efficient direct THz radiation detectors. Indeed, both types of the transistors have shown that once equipped with antennas, they can capture THz radiation from the open space and deliver the voltage/current proportional to incoming THz radiation power (THz rectification).Most of the work was dedicated to the field effect transistors that rectify THz radiation by plasma related nonlinearities. After pioneering work of [1-2] only very small attention was devoted to HBTs. In this work, we present experimental studies of THz detection by different HBTs fabricated using InP double HBT (DHBT) technologies [3]. Different devices were investigated: single-finger devices and multi-finger devices formed using equally spaced parallel single-transistor fingers [4]. We have evaluated the room temperature detection performances of the devices in the sub-THz range from 250 GHz up to 650 GHz and analyse in details the physical mechanisms of THz detection. Finally, THz domain is an excellent non-contact probe of water content in biological tissues [5]. We also show that the sensitive HBTs detectors can be used for THz spectroscopy and 2D THz imaging to study the water dynamics of sorghum (a grass species cultivated for its grain) by monitoring the dehydration kinetics of its leaves.

Ref HAL: hal-01923924_v1
DOI: 10.1109/IRMMW-THz.2018.8510443
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We present experimental studies of THz detection by different Heterojunction Bipolar Transistors (HBTs) fabricated using InP technology. We also show that the sensitive HBTs detectors can be used for THz spectroscopy and 2D THz imaging to study how the water content affects the polarization rate and biattenuation in fibrous sorghum leaf.

Ref HAL: hal-01923897_v1
DOI: 10.23919/MIKON.2018.8405293
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We consider a terahertz detector based on a graphene ballistic rectifier integrated with an antenna. The device demonstrates an extrinsic responsivity of hundreds of V/W in the range 70-440 GHz at room temperature with no indications of a cut-off frequency up to 0.44 THz. The device also demonstrates linear response for more than 3 orders of magnitude of power input due to its zero threshold voltage and its high saturation current.

Ref HAL: hal-01923604_v1
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A graphene ballistic rectifier is used in conjunction with an antenna to demonstrate a terahertz (THz) detector and imager. The device is used to take an image of an optically opaque object at 0.68 THz demonstrating potential in both medical and security imaging applications.

Ref HAL: hal-01862289_v1
DOI: 10.1103/PhysRevB.97.245419
WoS: WOS:000436036700007
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10 Citations
Résumé:

We report on temperature-dependent terahertz spectroscopy of a three-layer InAs/GaSb/InAs quantum well (QW) with inverted-band structure. The interband optical transitions, measured up to 16 T at different temperatures by Landau-level magnetospectroscopy, demonstrate the inverted-band structure of the QW. The terahertz photoluminescence at different temperatures allows us to directly extract the optical gap in the vicinity of the Γ point of the Brillouin zone. Our results experimentally demonstrate that the gap in the three-layer QWs is temperature independent and exceeds by four times the maximum band gap available in the inverted InAs/GaSb bilayers.

Ref HAL: hal-01740166_v1
Ref Arxiv: 1710.06666
DOI: 10.1103/PhysRevLett.120.086401
WoS: WOS:000425738500007
Ref. & Cit.: NASA ADS
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29 Citations
Résumé:

We report a direct observation of temperature-induced topological phase transition between trivial and topological insulator in HgTe quantum well. By using a gated Hall bar device, we measure and represent Landau levels in fan charts at different temperatures and we follow the temperature evolution of a peculiar pair of "zero-mode" Landau levels, which split from the edge of electron-like and hole-like subbands. Their crossing at critical magnetic field Bc is a characteristic of inverted band structure in the quantum well. By measuring the temperature dependence of Bc, we directly extract the critical temperature Tc at which the bulk band-gap vanishes and the topological phase transition occurs. Above this critical temperature, the opening of a trivial gap is clearly observed.

Commentaires: 5 pages + Supplemental Materials