We report on the high-field (up to 10T) magnetoresistance measurements performed on the short (down to 75-nm gate length) n-type Si metal-oxide-semiconductor field-effect transistors. The electron magnetoresistance mobility of these nanometer devices was determined for a wide range of the electron concentration (107–1013cm−2, i.e., from a weak to a strong inversion) and gate length (10μm–75nm). In the case of long samples, the magnetoresistance mobility was compared to the effective mobility obtained by the standard parameter extraction and the split C–V techniques. The results are discussed in terms of the scattering power-law two-dimensional transport analysis. The data clearly indicate a significant decrease of the mobility with the gate length reduction below 100nm.

We report on the depinning of nearly commensurate charge-density waves in 1T-TaS2 thin films at room temperature. A combination of the differential current–voltage measurements with the low-frequency noise spectroscopy provides unambiguous means for detecting the depinning threshold field in quasi-2D materials. The depinning process in 1T-TaS2 is not accompanied by an observable abrupt increase in electric current—in striking contrast to depinning in the conventional charge-density-wave materials with quasi-1D crystal structure. We explained it by the fact that the current density from the charge-density waves in the 1T-TaS2 devices is orders of magnitude smaller than the current density of the free carriers available in the discommensuration network surrounding the commensurate charge-density wave islands. The depinning fields in 1T-TaS2 thin-film devices are several orders of magnitude larger than those in quasi-1D van der Waals materials. Obtained results are important for the proposed applications of the charge-density wave devices in electronics.

By means of high-pressure Raman spectroscopy of coupled LO phonon-plasmon modes, a qualitatively new model of the metal-insulator transition observed in bulk GaN crystals at pressure around 20 GPa is proposed. This transition was interpreted recently as caused by the emergence of the localized donor state into the energy gap of GaN. Our new experimental evidence suggests that two types of donors can supply electrons to the bulk crystal: the first of a localized character and the second of a shallow character with contributions to the electron concentration of 5 x 10'' and 3 x 1Ol8 ~m -~, respectively. The localized state can be associated with the nitrogen vacancy, while the shallow state can be tentatively attributed to impurities such as oxygen. A number of interesting phenomena take place beyond the metal-insulator transition in bulk GaN and an attempt to explain them will be made in the present work.

We report magnetoconductivity experiments carried out on pseudomorphic AlGaAs/InGaAs/GaAs quantum wells in a wide range of magnetic fields (0.1 to 80 kG). Pressure-illumination cycles were used for tuning the free electron density. Measurements of the Shubnikov-de Haas and Hall effects allowed us to determine the transport and quantum relaxation times. Corrections to the magnetoconductivity due to weak localization and weak antilocalization were determined and used to calculate the phase and spin relaxation times. We analyzed phase, spin, quantum, and transport relaxation rates as a function of electron density which allowed for a characterization of the dominant scattering processes.

We consider a single spike of ferrofluid, arising in a small cylindrical container, when a vertically oriented magnetic field is applied. The height of the spike as well as the surface topography is measured experimentally by two different technologies and calculated numerically using the finite element method. As a consequence of the finite size of the container, the numerics uncovers an imperfect bifurcation to a single spike solution, which is forward. This is in contrast to the standard transcritical bifurcation to hexagons, common for rotational symmetric systems with broken up-down symmetry. The numerical findings are corroborated in the experiments. The small hysteresis observed is explained in terms of a hysteretic wetting of the side wall.

No abstract

Character of the metal-insulator transition which occurs at about 23 GPa in bulk GaN crystals has been studied by means of high pressure Raman spectroscopy. The related freeze-out of electrons is caused by the localized donor state formed by most likely oxygen and emerging at high pressures to the band gap of GaN. As a result, the electron concentration drops from its initial value of 5.1019 cm-3 to about 3. 1018 cm-3. These remaining electrons originate likely from another donor center with effective mass character, probably carbon. The obtained results raise a question whether the nitrogen vacancy is abundant enough to be observed in bulk GaN crystals.

We report both cw and time resolved optical investigations performed on an InGaN/GaN multiple quantum well grown by MOVPE on <0001>-oriented sapphire substrate. At low temperature we find a strong "blue" luminescence band, of which energy position corresponds well with the wavelength of stimulated emission when excited with a nitrogen laser. We show that this PL band appears systematically red-shifted with respect to the QWs features, which supports a standard picture of fluctuations of the indium composition. Coming to the time-resolved data, we find at low temperature at least two "blue" band components which are both associated with long decay times (up to 4-5 ns at 8K). The decay time is temperature dependent and, when rising the temperature, the recombination rate increases. At room temperature, we reach typical values in the range ~100 to 500 ps.