O. I. Kon’kov

Lithium intercalation into amorphous-silicon thin films: An electrochemical-impedance study

Lithium intercalation into 0.25-μm-thick films of amorphous silicon is studied using the electrochemical-impedance technique. An equivalent circuit, proposed for such electrodes, comprises the electrolyte resistance and three units connected in series, each unit being a parallel combination of a resistance and a constant-phase element. The units relate to the charge transfer processes at the silicon/electrolyte interface, charge transfer though the passive film on the silicon, and the lithium diffusion into the silicon bulk. During potential cycling, changes occur largely in the unit related to the passive film. The lithium diffusion coefficient in the amorphous silicon is estimated as ∼ 10−13 cm2 s−1.

Lithium intercalation in thin amorphous-silicon films

Electrochemical intercalation of lithium in thin films of amorphous hydrogenated silicon (a-Si:H), deposited at temperatures of 100 and 250°C on stainless-steel substrates, is studied. It is shown that the discharge capacity of films of identical thicknesses manufactured at a temperature of 250°C is greater than that for films produced at of 100°C. Dependence of the discharge capacity of the films manufactured at 250°C on their thickness is examined. It is established that an increase in the film thickness leads to acceleration of the decrease in the discharge capacity in the course of cycling. At a current density of 0.175 mA cm−2, the discharge capacity of films 0.25 and 1.35 μm thick equals nearly 2 Ah g−1 in a third cycle, whereas in a hundredth cycle it amounts to 1.10 and 0.37 Ah g−1, respectively. The diffusion coefficient for lithium in the films is equal to ∼10-13 cm2s−1.

Luminescence of erbium in amorphous hydrogenated silicon obtained by the glow-discharge method

We report the first observation of efficient room-temperature photoluminescence of erbium in amorphous hydrogenated silicon prepared by the plasma chemical-deposition method.

Excess leakage currents in high-voltage 4H-SiC Schottky diodes

The high-voltage 4H-SiC Schottky diodes are fabricated with a nickel barrier and a guard system in the form of “floating” planar p-n junctions. The analysis of I–V characteristics measured in a wide temperature range shows that the forward current is caused by thermionic emission; however, the current is “excessive” in the reverse direction. It is assumed that the reverse current flows locally through the points of the penetrating-dislocation outcrop to the Ni-SiC interface. The shape of reverse I–V characteristics makes it possible to conclude that the electron transport is governed by the monopolar-injection mechanism (the space-charge limited current) with participation of capture traps.

Lithium Intercalation into Amorphous Silicon Thin Films

Electrochemical lithium intercalation into a-Si:H thin films grown on stainless steel substrates at temperatures of 100 and 250°C was studied. The intercalation capacity of films grown at 250°C is ∼1750 and ∼500 mA h/g in the first and hundredth cycles. The lithium diffusivity in films is ∼ 10−12 cm2/s.

Photosensitive structures based on single-crystal silicon and phthalocyanine CuPc: Fabrication and properties

Vacuum thermal deposition of phthalocyanine CuPc onto the surface of crystalline silicon and subsequent magnetron sputtering of ZnO:Al are used to form n-ZnO:Al-p-CuPc-n-Si photosensitive structures for the first time. The highest photosensitivity of these structures SUm≈20 V/W is attained if the ZnO side of the structure is illuminated and is observed in the photon-energy range 1–3.2 eV at T=300 K. An induced photopleochroism is observed if the linearly polarized light is incident obliquely on the ZnO side; the magnitude of the photopleochroism oscillates as a result of the interference of linearly polarized light in the ZnO film. It is concluded that the suggested structures have prospects for use in broadband photoconverters of natural light and in rapidly tunable photoanalyzers of linearly polarized light.

I-V characteristics of high-voltage 4H-SiC diodes with a 1.1-eV Schottky barrier

The I-V characteristics of high-voltage 4H-SiC diodes with a Schottky barrier ∼1.1 eV in height are measured and analyzed. The forward I-V characteristics proved to be close to “ideal” in the temperature range of 295–470 K. The reverse I-V characteristics are adequately described by the model of thermionic emission at the voltages to 2 kV in the temperature range of 361–470 K if, additionally, a barrier lowering with an increase in the band bending in the semiconductor is taken into account.

Experimental 4H-SiC junction-barrier Schottky (JBS) diodes

Abstract4H-SiC junction-barrier Schottky (JBS) diodes have been fabricated with local p–n junctions under the Schottky contact formed by nonequilibrium diffusion of boron. Static and dynamic characteristics of the JBS diodes are compared with those of similar 4H-SiC Schottky diodes. It is shown that, compared with ordinary Schottky diodes, the JBS diodes have leakage currents that are, on average, a factor of 200 lower at the same reverse bias. The reverse recovery charge is the same for both types of diodes and equal to the charge of majority carriers removed from the n-type base region in switching.

Leakage currents in 4H-SiC JBS diodes

Leakage currents in high-voltage 4H-SiC diodes, which have an integrated (p-n) Schottky structure (Junction Barrier Schottky, JBS), have been studied using commercial diodes and specially fabricated (based on a commercial epitaxial material) test Schottky diodes with and without the JBS structure. It is shown that (i) the main role in reverse charge transport is played by SiC crystal structure defects, most probably, by threading dislocations (density ∼104 cm−2), and (ii) the JBS structure, formed by the implantation of boron, partially suppresses the leakage currents (by up to a factor of 10 at optimal separation, 8 μm between local p-type regions).

Percolation, self-organized criticality, and electrical instability in carbon nanostructures

The processes of avalanche formation, percolation, and electrical instability have been investigated experimentally using multi-walled and single-walled carbon nanotubes as an example. The performed investigations are based on the comparison of electrical conductivity dynamics in classical experiments, such as the “sand heap,” the two-dimensional grid of resistances with a stochastic node blocking, and the nanosecond percolation in a mode of electrical instability in nanotube tangles/granules. The regularities of mechanisms are revealed and the general concept is formulated.