We present an experimental study on the performance of nano-Hall sensors made on the two dimensional electron gaz of a pseudo morphic GaAlAs/GaInAs heterostructures. The active area of the sensor is from sub-micronic scale (down to 500 nm) to 5 microns. Ohmic contacts have micronic size, and a reference sample of 80 micron width has been caracterized as well, as a reference. In our process, we have improved the contacts technology to limit the thermal Shottky noise. Thus although ohmic contacts have small dimensions they have low resistance and do not limit the sensitivity of our nano-sensors. Extensive caracterization of those devices demonstrate a diffusive transport at 300 K, and a magnetic field sensitivity up to 1000 V/T/A. We have focused our attention on the smallest detectable magnetic field in the smallest sensor, and performed a systematic study of the noise measurements. We have measured the excess noise in both the longitudinal configuration and the Hall configuration, as a function of the current. Our noise measurements performed at room temperature in the range [1 Hz-100 kHz] show, at low frequency, an 1/f noise spectrum whose intensity is proportional to the square of the current. We understand our data by the conductivity fluctuations model and we obtain the Hooge parameter for this technology. We demonstrate that the noise intensity is inversely proportional to area of the sensor. Of course reducing the dimensions induces physical limitations but we demonstrate that a magnetic field of few μT can be measured with a micron scale sensor at low frequencies; at higher frequencies, when the thermal noise limits the resolution, the measurement of 300 nT is achievable

Nous publions un Brevet sur la production optimisée d'énergie électrique à partir d'eau chaude obtenue par chauffage solaire thermique. C'est une solution adaptée aux maisons individuelles.

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.

The direct closure of the quantum metrological triangle consists in achieving Ohm's law with the three effects used and investigated in quantum electrical metrology: the Josephson effect (JE), the quantum Hall effect (QHE) and the single-electron tunnelling effect (SET). The aim is to check the consistency of the phenomenological constants KJ, RK and QX associated with these effects and theoretically expressed with the fundamental constants e and h (elementary charge and Planck constant, respectively). Such an experiment is a contribution to a future redefinition of the International System of units (SI). In this paper, the experimental setup developed at LNE is described and the main obtained results are given. From a set of four measurements, agreement at a level of 1.3 parts in 105 was found between the quantum charge involved in the SET, i.e. QX, and the CODATA value of the elementary charge. The best measurement has shown a relative type-A uncertainty of 1.9 parts in 106, while the amplitude of the current generated by a metallic electron pump was as low as 3.6 pA.

Terahertz Detection of quantum cascade laser emission by plasma waves in Nano-transistors

Cyclotron resonance spectra of 2D electrons in HgTe/CdxHg1−xTe (0 1 3) quantum well (QW) heterostructures with inverted band structure have been thoroughly studied in quasiclassical magnetic fields versus the electron concentration varied using the persistent photoconductivity effect. The cyclotron mass is shown to increase with QW width in contrast to QWs with normal band structure. The measured values of cyclotron mass are shown to be systematically less than those calculated using the 8 × 8 Kane model with conventional set of HgTe and CdTe material parameters. In quantizing pulsed magnetic fields (Landau level filling factor less than unity) up to 45 T, both intraband (CR) and interband magnetoabsorption have been studied at radiation wavelengths 14.8 and 11.4 µm for the first time. The results obtained are compared with the allowed transition energies between Landau levels in the valence and conduction bands calculated within the same model, the calculated energies being again systematically less (by 3-14%) than the observed optical transition energies.

We report on investigations of photovoltaic response of Si-MOSFETs subjected to terahertz radiation in high magnetic fields. Then a DC drain-to-source voltage is developed that shows singularities in magnetic fields corresponding to paramagnetic resonance conditions. These singularities are investigated as a function of incident frequency, temperature and two-dimensional carrier density. We tentatively attribute these resonances to spin transitions of the electrons bound to Si dopants and discuss the possible physical mechanism of the photovoltaic signal generation