No abstract available

[en] Voltage generation in strong magnetic fields (0 to 6 T) in HgTe and n-InSb under far-infrared illumination is observed. The fine structure of the observed voltage versus the magnetic field is interpreted as being due to transitions between Landau sublevels. A new method of experimental determination of the nature of the observed voltage is presented. It is shown that for both the materials investigated, the observed phenomenon is due to the optically-induced Nernst-Ettinghausen effect. From the qualitative analysis it is concluded that at low temperatures and in quantisizing magnetic fields, the phonon drag is the main process responsible for the observed voltage in both, InSb and HgTe. (author)

[en] With the use of the magnetically tunable far infrared sources utilizing the cyclotron resonance emission in InSb and InP, the photoconductive spectroscopy of shallow donors in InP was performed. The experiments were performed in the spectral region from 40 cm^-1 to 110 cm^-1 and at the magnetic fields up to 6 T. Significant dependence of the photoconductive amplitudes due to the 1s-2p_±,0 transitions on the electric field was observed and discussed. 8 refs., 4 figs. (author)

[en] Week localization corrections to conductivity of two-dimensional electron gas are studied by measurements of magnetic field dependence of the conductivity in GaInAs quantum wells. We observed that, when presented as a function of the normalized magnetic field (x=B/B_tr where B is the magnetic field, B_tr=h/4eτD, D is the diffusion constant and τ is momentum relaxation time), different samples show very similar high field behaviour. A theoretical description is developed that allows one to describe in a consistent way and low field behaviour. The theory predicts universal (B^-1/2) behaviour of the conductivity correction for all 2D systems in high field limit (x>1). Low field behaviour depends strongly on spin and phase relaxation mechanisms. Comparison of the theory with experiment confirms the universal behaviour in the high field limit and allows one to estimate the spin and phase relaxation times for different GaInAs quantum wells. (author)

No abstract available

[en] We present the possibility of using magnetic field to enhance responsivity and to tune spectral range of far-infrared InSb detector (Based on photoconductivity effect) beyond its standard range limited to about 30 cm^-1. We show that due to cyclotron resonance assisted transitions we can use it as a tunable detector working up to energies about 180 cm^-1 (22 MeV). We have used such detector as a spectrometer for measurements of the Landau emission from GaAs emitter. (author)

[en] We report on terahertz detection by two-dimensional electron plasma located in nanometric InGaAs and GaN transistors. Up to now, the biggest part of the research was devoted to GaAs-based devices as the most promising from the point of view of the electron mobility. The resonant detection was reported, however, only in the sub-THz range. According to predictions of the Dyakonov-Shur plasma wave detection theory an increase of the detection frequency can be achieved by reducing the length or increase the carrier density in the gated region. We demonstrate that the 1THz limit can be overcome by using ultimately short gate InGaAs and GaN nanotransistors. For the first time the tunability of the resonant signal by the applied gate voltage is demonstrated. We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel (Dyakonov-Shur theory). We also show that by increasing of the drain-to-source current leads to a transformation of the broadband detection to a resonant and tuneable one. We can get resonant detection at room temperature. We finally discuss the possible application of detection by nanotransistors in different types of THz spectroscopy research

[en] For ten various brands of flour contents of chosen (heavy) elements were determined by means of ICP, GF-AAS, PIXE and ASV/CSV methods. General performance of participating laboratories as well as pros and cons of different analytical methods were compared and discussed. (author). 6 refs, 6 figs, 7 tabs

[en] The high electron mobility transistors can act as a resonator cavity for the plasma waves that can reach THz frequencies for a nanometer size devices. As was predicted by Dyakonov and Shur in 1993, the steady state of the current flow in a gated 2D electron gas can become unstable leading to the emission of the electromagnetic radiation at the plasma wave frequencies. The theory predicted also that the plasma waves can be used for resonant detection of THz electromagnetic radiation. In the present paper we review our recent experiments on THz emission and detection performed on high electron mobility transistors based on different semiconductor structures: InGaAs/GaAs, GaAs/GaAlAs and Si. (author)

[en] Electron transport and photoresponse in the terahertz range in a GaN/AlGaN field-effect transistor with the submicrometer gate (0.25 μm) and two-dimensional electron gas in the channel (the electron concentration n_s = 5 x 10¹² cm^-2) were studied at 4.2 K. The charge-carrier mobility in the transistor's channel μ = 3500 cm²/(V s) was determined from the dependence of the conductance on magnetic field. It is found that the dependence of photovoltage at the radiation frequency f = 574 GHz on the gate voltage (i.e., on the concentration of two-dimensional electrons) features a characteristic maximum, which is related to a resonance response of the subgate plasma in the transistor channel