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Temperature-dependent decline in the external quantum efficiency (EQE) of blue light-emitting diodes, which is at a maximum at j 40 A/cm2 the decline in the external quantum efficiency in the continuous-wave and pulsed modes is determined by the loss in nonequilibrium filling by delocalized carriers of states associated with the lateral inhomogeneities in the composition of the solid solution outside the space-charge region, as well as by the loss due to the interaction of delocalized carriers with extended defects.

Low frequency noise is studied in 4H-SiC power metal-oxide-semiconductor field-effect transistors (MOSFETs) irradiated with 15-MeV protons. Irradiation is carried out at room temperature in the frequency range from 1 Hz to 50 kHz upon irradiation with doses Φ of 1012 to 6 × 1013 cm–2. The frequency dependence of the spectral noise density SI follows the law SI ∝ 1/f with good accuracy. A correlation between the saturation current of the output characteristic Id(Vd) and the low-frequency noise level is traced. At doses in the range 1012 cm–2 ≤ Φ ≤ 6 × 1013 cm–2, the saturation current varies within about 20%, whereas the noise level changes by two orders of magnitude. The results of noise spectroscopy are used to estimate the trap density in the gate oxide, Ntv. In unirradiated structures, Ntv ≈ 5.4 × 1018 cm–3 eV–1. At Φ = 6 × 1013 cm–2, Ntv increases to ~7.2 × 1019 cm–3 eV–1.

It is established experimentally that noticeable changes in the I–V characteristics and low-frequency noise in 4H-SiC pin diodes irradiated by electrons with an energy of 0.9 MeV are observed after doses of Φ ≥ 1.4 × 1015 cm–2. The currents in the forward and reverse branches of the I–V characteristics vary nonmonotonically at voltages lower than 2 V with increasing dose, which is explained by the interaction between the excited electronic subsystem and metastable defects. In this case, a steady increase in the ideality factor and the series resistance of diodes in the region of exponential growth of the I–V characteristics at voltages exceeding 2 V is observed. The reliable operation of microwave devices with low-noise 4H-SiC pin diodes under conditions of electron irradiation is possible up to a cumulative dose of Φ ≤ 1015 cm–2. In microwave devices, the level of low-frequency noise in which is irrelevant but the stabile regime of parameters is of importance, the dose can be increased to Φ ≈ 8 × 1015 cm–2.

A fractal-percolation system that includes extended defects and random fluctuations in the alloy composition is formed during the growth of device structures based on Group-III nitrides. It is established that the specific features of this system are determined not only by the growth conditions. It is shown that the diversity of the electrical and optical properties of InGaN/GaN LEDs (light-emitting diodes) emitting at wavelengths of 450–460 and 519–530 nm, as well as that of the electrical properties of AlGaN/GaN HEMT (high-electron-mobility transistor) structures, is due to modification of the properties of the fractal-percolation system both during the growth process and under the action of the injection current and irradiation. The influence exerted by these specific features on the service life of light-emitting devices and on the reliability of AlGaN/GaN HEMT structures is discussed.

The obtained experimental results allow us to clarify the nature of mechanisms related to the presence of cations in disordered InGaN alloy and hetero-interfaces. The capture of charge carriers by cations reduces the external quantum efficiency (EQE) in green MQWs at j < 10 A/cm2. The EQE droop phenomenon caused by smoothed out lateral potential fluctuations occurs at j > 10 A/cm2. At j > 40 A/cm2 the droop associated with interactions between charge carriers and dislocations and grain boundaries takes place.

In this work, the modification of the surface parameters of graphene chips after electrolysis treatment in a NaClO4 aqueous solution has been studied. Two electrolysis modes have been analysed. In the first one, a negative potential (-0.2 V) is applied to the graphene chips, while in the second one the potential is positive (0.8 V). Investigation using a number of techniques including atomic force microscopy, Kelvin probe force microscopy, Raman spectroscopy, measurements of current-voltage characteristics and low-frequency noise has shown that the electrolysis mode with application of a positive potential on graphene chips decreases the 1/f noise and allows one to obtain a uniform surface potential distribution while leaving the graphene structure undamaged. The results of this study help to understand the efficiency and reproducibility of the procedure for electrolysis treatment of graphene chips.

The contribution of several mechanisms to the external quantum efficiency (EQE) droop in blue InGaN/GaN LEDs occur at different current densities j and voltages in MQWs situated inside and outside of a depletion region around p-n junction. It is clarified that an increase in EQE droop at 300-400 K (j < 10 A/cm2) is due to non-radiative losses related to an enhancement in trap-assisted tunneling. It is also associated with a growth in the concentration of delocalized carriers. The main source of the EQE droop under direct current and at pulse mode when j > 30 A/cm2 is non-equilibrium filling of lateral regions of different size within MQWs placed outside of depletion region by delocalized carriers activated by injection when voltage exceed a threshold value (U > Uth). This leads to a decrease in localized potential and to the blue shift of EQE maximum over wavelengths followed by the EQE droop.

It is shown that a three-dimensional fractal–percolation system is formed in nanomaterials of light-emitting InGaN/GaN and AlGaN/GaN structures in the presence of conducting extended defects and local inhomogeneities of the composition of the solid solutions; this system determines the electrophysical properties of light-emitting diodes fabricated on the basis of these structures. The geometry and properties of this system depend nonlinearly on the degree of disorder in the nanomaterial of the structures, on the value of the injection current, and on the rate of alloy growth.

Functionalization of graphene/SiC dies by nitro-phenyl and its reduction to phenyl-amine is discussed. The graphene films were formed on a SiC substrate by the substrate surface thermal decomposition at 1800-2000°C. The functionalizing procedure included a two-step electrochemical process monitored by cyclic voltammetry and the die resistance. Functionalized graphene/SiC dies with applied antibody were blood sensitive and can be potentially applied to identify promptly types of the blood.

A comparative study of the degradation of HVPE-grown 360 nm AlGaN/GaN UV and commercially available InGaN/GaN blue LED chips was performed. The common feature of the degradation of these two types of LEDs was found to be the increase of the conductivity of shunt paths under current injection. The paths (shunts) are localized in the extended defects system (EDS). It is proposed that the conductivity increase is due to defect formation under multiphonon carriers recombination in a part of the EDS enriched by Ga or In atoms. This process is accompanied by a local overheating and migration of Ga or In atoms. To increase the lifetime of the AlGaN/GaN UV LEDs to more than 2000 h it is necessary to improve their nano-structural and nanoscale AlGaN composition ordering. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The 1/ f noise has been investigated for the first time at 300 and 77 K in high-quality 4H-SiC Schottky diodes. It is shown that, at 77 K, the dependence of the spectral noise density on current, S I ( I ), differs fundamentally between the cases of the current flowing through the main part of the diode with a comparatively high barrier and the current flowing through the nano-sized patches with a comparatively low barrier.

Some green light emitting diodes (LEDs) based on GaN/InGaN multiquantum-well (MQW) structures exhibit strong frequency and temperature dependence of capacitance and prominent changes in capacitance–voltage profiles with temperature that make it difficult to obtain reliable deep level transient spectroscopy (DLTS) measurements. DLTS performed at low probing signal frequency and with constant capacitance between the measurements by controlling applied bias mitigates these issues. This allows measurement of deep electron and hole traps in specific quantum wells (QWs) in the MQW structure. The dominant electron and hole traps detected have levels near Ec− (0.45–0.5) eV and Ev+ (0.6–0.63) eV. Their density increases significantly after aging for a long period (2120 h) at high driving current and elevated temperature. The reason for the observed anomalies in DLTS spectra of these green LEDs is the high density of states in the QWs with activation energies near 0.08, 0.12–0.14, and 0.3 eV, detected in admittance spectra, and, for the 0.08 eV and 0.3 eV, these states are likely related to defects.

The results of the degradation study of commercial InGaN/GaN LEDs with the external quantum efficiency (EQE) ∼ 40–50 % at 450–460 nm are presented. It has been clarified that one of the mechanisms responsible for EQE degradation and the unpredictable failure of LEDs is the multiphonon recombination of carriers. The distorted forward branch of I-V characteristics at U < 2V and the appearance of the SI ∼j4 section on the current spectral noise density dependences on current density in LEDs before or after 100 hours of aging test are the criteria identifying an unpredictable failure.

Study of the spectral noise density and its dependence on current density in as-fabricated and degraded blue light-emitting diodes (LEDs) based on InGaN/GaN quantum-well structures are reported. It is shown that defects are generated nonuniformly in the course of degradation, being concentrated along extended defects penetrating into the active region of LEDs. It is demonstrated that the decrease in the external quantum efficiency in the course of aging is due to the enhancement of charge transport uniformity, which leads to the formation of shunts and local overheating regions. Typically, in blue LEDs, these effects are responsible for the ambiguous development of the degradation process, which hinders prognostication of LED service life. The effect of noise suppression is observed in a narrow current density range (10−2 to 10−1 A cm−2) corresponding to the onset of radiative recombination.

A comprehensive study of blue lightemitting diodes based on quantumwell InGaN/GaN struc� tures with external quantum efficiencies η of up to 40% has been carried out. It is shown that, in the general case, the manner in which the efficiency depends on the current density j is determined by the competition of contributions to the radiative recombination of localized and delocalized carriers. The contribution of the latter grows with worsening structural organization of the nanomaterial, increasing temperature and drive current, and decreasing width of the depleted layer in the active region (under zero bias). The steepest effi� ciency droop relative to the maximum value (by up to a factor of 2 at j ≈ 50 A cm -2 ) is observed in the case of heavy doping of the n + �region (to 10 19 cm -3 ) and upon appearance of compensated layers in the active or p + �region. At j > 50 A cm -2 , the contribution of delocalized carriers is predominant and the current dependences of efficiency are of uniform type, approximated with η(j) ∝ j -b , where 0.2 < b < 0.3.

Irradiation with 6 MeV electrons of near-UV (peak wavelength 385–390 nm) multi-quantum-well (MQW) GaN/InGaN light emitting diodes (LEDs) causes an increase in density of deep electron traps near Ec−0.8 and Ec−1 eV, and correlates to a 90% decrease of electroluminescence (EL) efficiency after a fluence of 1.1 × 1016 cm−2. The likely origin of the EL efficiency decrease is this increase in concentration of the Ec −0.8 eV and Ec −1 eV traps.

It is established that the low-frequency noise density S in InGaN/GaN based light-emitting diodes (LEDs) operating a current densities j > 20 A/cm2 depends on the current density as S ∼ j3. This dependence is indicative of the formation of new nonradiative recombination centers, which may account for a drop in the external quantum efficiency of LEDs operating at high current densities.

The new method magnetotherapy is used for greater efficacy of pathogenetic treatment of chronic hepatitis in children. Dynamic observation of patients shows the improvement of metabolic and hemodynamic changes after impulse magnetotherapy in earlier terms than after basic therapy. The data obtained indicate the stimulating effect of impulse magnet field on recreative processes in the liver.

It was shown that the contribution of 3D nanoscale indium fluctuations into the efficiency droop at j 50 A/cm2 and the current dependences of efficiency, approximated by as η (j) α j-b where 0.2 < b < 0.3, are alike in both green and blue LEDs.

The obtained results demonstrate that the improvement of nanomaterial arrangement in AlGaN/GaN HEMT structures quantitatively characterized with the use of a multifractal parameter (the degree of disorder) results in the increase at several times in the electron mobility values at 2DEG channel in HEMT structures and the reliability of HEMT parameters.

The activity of liver monoxygenase system was studied in 94 children with various clinical forms, activities and duration of chronic hepatitis by the antipyrine test and the diagnostic and prognostic significance of this test was assessed. The test is recommended for the assessment of the liver process severity and for the prediction of the disease course in children.

Surface charge of the peripheral blood red cells was studied with the device for cellular phoresis in 36 schoolchildren suffering from chronic hepatitis and 20 healthy children. The surface charge was found regularly reduced when the disease exacerbated, this permitting a judgement on the activity of the hepatic process. The developed method for rapid diagnosis of chronic hepatitis is recommended to be used during the outpatient stage of examinations and for the assessment of membranotropic therapy efficacy.

Activities of red cell glutathione-dependent enzymes, glutathione peroxidase (GP), glutathione reductase, and glutathione transferase (GT), were measured in 70 children suffering from chronic hepatitis and liver cirrhosis with various forms and activities of the conditions. Manifest changes in GP and GT activities were revealed. Measurements of GT activities are recommended for assessment of the liver process severity and for early detection of the liver detoxifying function stress.

Altogether 58 children with chronic hepatitis were examined for specific C31- and Fc-dependent neutrophil adhesion. Considerable alterations were found as dependent on the disease pattern and the degree of the pathological process activity in the liver. The data obtained promote verification of the pathogenesis of chronic hepatitis in children.