A model of the turn-on spread has been developed for the axisymmetric configuration characteristic of the optical triggering of power SiC thyristors. Results for plane- and axisymmetric cases are compared. It is shown that the initial stage of the spread, during ∼ (2–3)τ, where τ is the current rise time constant for the thyristor turn-on, is characterized by a relatively low spread velocity, especially in the axisymmetric case. It is demonstrated that, even for a comparatively large thyristor structure, self-similarity conditions are not valid even for the plane case.

We report on the observation of a new effect—the appearance of a galvanic signal in the narrow-gap semiconductor Pb _{1- x}Sn _x Te(In) in the magnetic field under the action of strong 100 ns-long terahertz laser pulses. The signal changes its sign and kinetics as the temperature increases from 4.2 K to 25 K. This semiconductor possesses inversion symmetry of the crystalline lattice making impossible the observation of the magnetophotogalvanic effect which looks similar in its experimental manifestation. On the other hand, the laser quantum energy is much less than the bandgap of the semiconductor making the effect considerably different from the conventional Kikoin–Noskov photoelectromagnetic effect. Possible mechanisms responsible for the appearance of the effect are discussed.

We show that a metallic surface state is formed on Tl/Ge(111)-(1 × 1). The surface state forms electron pockets around of the surface Brillouin zone. A first-principles calculation reveals that the electron pockets are composed of a single branch of a spin-split surface-state band. The spin quantization axis is along the surface normal and inverts according to the time-reversal symmetry. Since this spin-split branch is the unique metallic band on this surface, the surface conductivity should be governed by this spin-split branch, suggesting a possible spin-polarized electric current.

The a-axis lattice parameter of Bi ₂Se ₃ is almost identical to the lattice periodicity of the InP (1 1 1) surface. We consequently obtain remarkably smooth Bi ₂Se ₃ (0 0 0 1) layers in hot-wall-epitaxy growth on InP (1 1 1)B substrates. The lattice-matched periodicity is preserved in the [1 1 0] and [ ] directions of the (0 0 1) surface. The Bi ₂Se ₃ layers grown on InP (0 0 1) substrates exhibit 12-fold in-plane symmetry as the [ ] direction of Bi ₂Se ₃ is aligned to either of the two directions. When the (1 1 1)-oriented InP substrates are inclined, the Bi ₂Se ₃ (0 0 0 1) layers are found to develop steps having a height of ∼50 nm. The tilting o...

The crystallization enthalpy measured in a large series of amorphous silicon (a-Si) materials varies within a factor of 2 from sample to sample (Kail et al 2011 Phys. Status Solidi RRL 5 361). According to the classical theory of nucleation, this variation should produce large differences in the crystallization kinetics leading to crystallization temperatures and activation energies exceeding 550 °C and 1.7 eV, respectively, the ‘standard’ values measured for a-Si obtained by self-implantation. In contrast, the observed crystallization kinetics is very similar for all the samples studied and has no correlation with the crystallization enthalpy. This discrepancy has led us to propose that crystallization in a-Si begins in microscopic domains that are almost identical in all samples, independently of their crystallization enthalpy. Probably the existence of microscopic inhomogeneities also plays a crucial role in the crystallization kinetics of other amorphous...

Carbon nanotubes (CNTs) are well known as materials for nanoelectronics and show great potential to be used as the sensing elements in chemical and biological sensors. Recently, CNTs have been shown to be effective nanofluidic channels and the transport of substances through small diameter CNTs is intrinsically fast, selective, and operates at the single molecule level. It has been shown that the transport characteristics of semiconducting single-walled CNT (SWCNT) field effect transistors (FETs) are sensitive to internal water wetting. We report here that the characteristics of semiconducting SWCNT FETs are also sensitive to the concentration, pH and ion type of the ionic solution when the electrolyte is inside the CNT. Such sensitivity is not observed at the outside surface of a semiconducting SWCNT. This opens a new avenue for building new types of CNT sensor devices in which the SWCNT concurrently functions as a nanochannel and an electronic detector.

In this work we report on the electrical characterization of nonpolar cubic GaN metal–insulator–semiconductor (MIS) structures. Si ₃N ₄ layers were deposited in situ on top of cubic GaN grown on 3C–SiC (0 0 1) substrates. The electric characteristics of the MIS structures are determined by current–voltage measurements and by capacitance and admittance spectroscopy techniques. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) was used to investigate the composition of our samples. From the flat band voltage in the MIS capacitors and a detailed band diagram analysis, the conduction band discontinuity of Si ₃N ₄ and cubic GaN was evaluated 1.17 eV, which is slightly lower than reported for hexagonal GaN. By admittance spectroscopy interface state densities are calculated. Current–voltage characteristics were used to evaluate the influence of the substrate temperature on the insulating properties of the MIS structures. The energe...

A general procedure is presented for the evaluation of the modes of a thin annular scalar source, whose angular mutual intensity is of the Schell-model type. Starting from the knowledge of the modes, the coherence properties of the field propagated from the source in paraxial conditions can be evaluated. When the propagated field is collimated by a suitable converging lens, presented results apply to the synthesis of propagation-invariant partially coherent beams.

We demonstrate how an electrode–molecule–electrode junction can be controllably opened and closed by careful tuning of the contacts’ interspace and voltage. The molecule, an octanethiol, flips to bridge a ∼1 nm interspace between substrate and scanning tunnelling microscope tip when an electric field exceeds a threshold (switch ‘on’). Reducing the field below this threshold value leads to the reproducible detachment of the octanethiol (switch ‘off’). Once contacted, a further reduction of the contacts’ interspace leads to an increase of the conductance of the molecule.

The relation between the tunnelling current I _t and the interaction energy/force E in an atomic-scale contact is discussed in the framework of a theoretical model established here. According to our model, we predict the existence of two characteristic scaling regimes, where the tunnelling current is either proportional to the interaction energy, I _t ∼  E, or to the square of the interaction energy, I _t ∼  E ². We show that the existence of a given regime is basically controlled by two parameters: (i) the energy degeneracy Δ and (ii) the hopping t between electronic levels involved in the interaction process. In addition, we discuss the validity of the Bardeen method to determine the tunnelling current in the short tip–sample distances.