The results of magnetoconductivity measurements in GaInAs quantum wells are presented. The observed magnetoconductivity appears due to the quantum interference, which lead to the weak localization effect. It is established that the details of the weak localization are controlled by the spin splitting of electron spectra. A theory is developed which takes into account both linear and cubic in electron wave vector terms in spin splitting, which arise due to the lack of inversion center in the crystal, as well as the linear terms which appear when the well itself is asymmetric. It is established that, unlike spin relaxation rate, contributions of different terms into magnetoconductivity are not additive. It is demonstrated that in the interval of electron densities under investigation ((0.98 − 1.85)·1012 cm −2 ) all three contribution are comparable and have to be taken into account to achieve a good agreement between the theory and experiment. The results obtained from comparison of the experiment and the theory have allowed us to determine what mechanisms dominate the spin relaxation in quantum wells and to improve the accuracy of determination of spin splitting parameters in A3B5 crystals and 2D structures. 73.20.Fz,73.70.Jt,71.20.Ej,72.20.My

22 pages, 12 figures, review paperInternational audienceResonant frequencies of the two-dimensional plasma in FETs increase with the reduction of the channel dimensions and can reach the THz range for sub-micron gate lengths. Nonlinear properties of the electron plasma in the transistor channel can be used for the detection and mixing of THz frequencies. At cryogenic temperatures resonant and gate voltage tunable detection related to plasma waves resonances, is observed. At room temperature, when plasma oscillations are overdamped, the FET can operate as an efficient broadband THz detector. We present the main theoretical and experimental results on THz detection by FETs in the context of their possible application for THz imaging

A dramatic increase of the conduction band electron mass in a nitrogen-containing III–V alloy is reported. The mass is found to be strongly dependent on the nitrogen content and the electron concentration with a value as large as 0.4m0 in In0.08Ga0.92As0.967N0.033 with 6×1019 cm−3 free electrons. This mass is more than five times larger than the electron effective mass in GaAs and comparable to typical heavy hole masses in III–V compounds. The results provide a critical test and fully confirm the predictions of the recently proposed band anticrossing model of the electronic structure of the III–N–V alloys.

Dislocation-free high-quality AlGaN/GaN heterostructures have been grown by molecular-beam epitaxy on semi-insulating bulk GaN substrates. Hall measurements performed in the 300 K–50 mK range show a low-temperature electron mobility exceeding 60 000 cm2/V s for an electron sheet density of 2.4×1012 cm−2. Magnetotransport experiments performed up to 15 T exhibit well-defined quantum Hall-effect features. The structures corresponding to the cyclotron and spin splitting were clearly resolved. From an analysis of the Shubnikov de Hass oscillations and the low-temperature mobility we found the quantum and transport scattering times to be 0.4 and 8.2 ps, respectively. The high ratio of the scattering to quantum relaxation time indicates that the main scattering mechanisms, at low temperatures, are due to long-range potentials, such as Coulomb potentials of ionized impurities.

Room temperature terahertz (far infrared) radiation emission from double grating coupled GaInAs∕AlGaAs∕GaAs heterojunctions is reported. Theoretical calculations of plasmon absorption spectrum are performed using a first principles electromagnetic approach. They correctly reproduce the frequency range and overall shape of the main (broad-band) part of the experimental spectra. The results clearly indicate that important part of the observed room temperature terahertz emission spectra can be due to the radiative decay of hot two-dimensional plasmons in the grating structure.

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This paper reviews recent advances in our original 2D-plasmon-resonant terahertz emitters. The structure is based on a high-electron-mobility transistor and featured with doubly interdigitated grating gates. The dual grating gates can alternately modulate the 2D electron densities to periodically distribute the plasmonic cavities along the channel, acting as an antenna. The device can emit broadband terahertz radiation even at room temperature from self-oscillating 2D plasmons under the DC-biased conditions. When the device is subjected to laser illumination, photo-generated carriers stimulate the plasma oscillation, resulting in enhancement of the emission. The first sample was fabricated with standard GaAs-based heterostructure material systems, achieving room temperature terahertz emission. The second sample was fabricated in a double-decked HEMT structure in which the grating gate metal layer was replaced with the semiconducting upper-deck 2D electron layer, resulting in enhancement of emission by one order of magnitude.

We report on high magnetic fields (up to 40 T) cyclotron resonance, quantum Hall effect and Shubnikov-de-Hass measurements in high frequency transistors based on Si-doped GaN–AlGaN heterojunctions. A simple way of precise modelling of the cyclotron absorption in these heterojunctions is presented. We clearly establish two-dimensional electrons to be the dominant conducting carriers and determine precisely their in-plane effective mass to be 0.230±0.005 of the free electron effective mass. The increase of the effective mass with an increase of two-dimensional carrier density is observed and explained by the nonparabolicity effect.