St.Petersburg, Russia
St.Petersburg, Russia

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Polyakov A.Y.,Institute of Rare Metals | Smirnov N.B.,Institute of Rare Metals | Govorkov A.V.,Institute of Rare Metals | Amano H.,Nagoya University | And 5 more authors.
Applied Physics Letters | Year: 2011

The correlation of integrated microcathodoluminescence efficiency with crystalline quality and deep trap density of nonpolar GaN films grown by metal organic chemical vapor deposition on semi-insulating 6H-m-SiC or r-sapphire is analyzed. The results suggest a strong influence of nonradiative recombination centers whose concentration decreases with decreased density of extended defects. Electron traps with energy levels at Ec -0.6 eV and which pin the Fermi level in films with high defect density are the most likely candidates for the decrease in light emission efficiency in nonpolar GaN. © 2011 American Institute of Physics.


Smirnov S.A.,Soft Impact Ltd. | Kalaev V.V.,Soft Impact Ltd. | Hekhamin S.M.,NPF Comterm Ltd. | Krutyanskii M.M.,NPF Comterm Ltd. | And 2 more authors.
High Temperature | Year: 2010

Results are given of numerical simulation of electromagnetic stirring of metal melt in a dc arc furnace. The flow pattern and the transport of passive admixture in baths with one and two electrodes are studied. The mathematical model describes three-dimensional turbulent flow of electrically conducting liquid in the field of gravitational and electromagnetic forces. The parameters of turbulence are calculated in two approximations, namely, unsteady-state approximation by the large eddy simulation (LES) model and quasisteady-state approximation by the k-ε model. © 2010 Pleiades Publishing, Ltd.


Stellmach J.,TU Berlin | Pristovsek M.,TU Berlin | Sava O.,TU Berlin | Schlegel J.,TU Berlin | And 2 more authors.
Journal of Crystal Growth | Year: 2011

The growth rates and aluminium contents of Al xGa 1-xN layers grown in a close-coupled showerhead reactor were investigated as a function of growth pressure and chamber height during metal-organic vapour phase epitaxy. The data show strong non-linear dependencies due to nanoparticle formation in the gas-phase. Good agreement between the experimental data and modeling results is obtained when the contribution of both Ga- and Al-containing species to the gas-phase particle formation is considered. © 2010 Elsevier B.V.


Mokhov E.N.,RAS Ioffe Physical - Technical Institute | Roenkov A.D.,RAS Ioffe Physical - Technical Institute | Segal A.S.,Soft Impact Ltd
Materials Science Forum | Year: 2013

The growth kinetics of SiC crystals doped with Al and Ga impurities and grown by the sublimation sandwich method at a small spacing between the source and the seed (<1 mm) has been studied. Dependence of an Al-doped SiC crystals growth rate on the clearance is shown to be non- monotonic and exhibits maximum at the clearance about of 100-300 μm. Such dependence is also observed for growth of pure and Ga-doped SiC crystals but only on (0001)Si face. The derived dependencies suggest that there are some considerable kinetic limitations of the SiC growth rate. High quality SiC crystals with such high concentration of the Al impurity as 2x1021 cm-3 were grown. © (2013) Trans Tech Publications, Switzerland.


Lundin W.V.,RAS Ioffe Physical - Technical Institute | Davydov D.V.,RAS Ioffe Physical - Technical Institute | Zavarin E.E.,RAS Ioffe Physical - Technical Institute | Popov M.G.,Russian Academy of Sciences | And 7 more authors.
Technical Physics Letters | Year: 2015

The paper presents results on optimizing the MOVPE technology of light-emitting diode (LED) structures in a Dragon-125 system to accelerate the technological cycle. Due to the high growth rate of GaN layers and optimization of the initial GaN growth phase, the total duration of the epitaxial process is reduced from 4 h 45 min to 2 h 44 min. The LED diode structures grown by this technique compare well in quality with LEDs grown by the standard method in the commercially available AIX2000HT system. © 2015, Pleiades Publishing, Ltd.


Bulashevich K.A.,Soft Impact Ltd. | Karpov S.Y.,Soft Impact Ltd.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2014

Using simulations, we have identify the major factors controlling the conversion efficiency of single-junction n-GaN/i-InxGa1-xN/p-GaN solar cells, including absorptivity of solar radiation, heterostructure polarity, composition of the InGaN active layer, and non-radiative life-times of generated electrons and holes. The interplay of these factors, their hierarchy, and the possible effect of stress relaxation in InGaN on the conversion efficiency are discussed in terms of modeling. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Durnev M.V.,Russian Academy of Sciences | Omelchenko A.V.,Russian Academy of Sciences | Yakovlev E.V.,Soft Impact Ltd. | Evstratov I.Y.,Soft Impact Ltd. | Karpov S.Y.,Soft Impact Ltd.
Physica Status Solidi (A) Applications and Materials Science | Year: 2011

Strain effect on indium incorporation and optical transitions in bulk InGaN and GaN/InGaN/GaN quantum wells (QWs) coherently grown on GaN substrates with different orientations of hexagonal axis is studied by simulation. The strain modification in the nonpolar and semipolar structures, as compared to polar ones, is found to result in both a higher indium percentage in the InGaN alloy and a larger materials bandgap, producing opposite trends in variation of the optical transition energy (emission wavelength) with the crystal orientation. The interplay between the effects is discussed in view of development of green-light emitters. A possible way for controlling the strain in the InGaN layers and QWs and thus the emission wavelength is considered and tested by modelling. Optical transition energy of the same single InGaN QW grown on either GaN or relaxed In 0.08Ga 0.92N sublayer as a function of the crystal C-axis inclination to epitaxial layer plane. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Karpov S.Yu.,Soft Impact Ltd.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

Recent progress in III-nitride LED modeling is reviewed with the focus on physical models that provide a better understanding of such hot issues, as factors limiting the internal quantum efficiency of light emission and high-current efficiency droop, polarization doping in graded-composition III-nitride alloys and its utilization in LEDs, current crowding in LED dice and its impact on the light extraction efficiency, and optimal light conversion in white LED lamps. Specific features of III-nitride materials, their impact on the LED operation, and models accounting for these features are considered. Insufficient understanding of transport mechanisms of non-equilibrium electrons and holes and their localization in InGaN inhomogeneous active regions are discussed along with other still unsolved problems. Influence of technological factors on LED heterostructures and their operation is argued in the context of further model developments. © 2011 SPIE.


Karpov S.Y.,Soft Impact Ltd.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

State-of-the art light-emitting diodes (LEDs) for solid-state lighting (SSL) are reviewed with the focus on their efficiency and ways for its improvement. Mechanisms of the LED efficiency losses are considered on the heterostructure, chip, and device levels, including high-current efficiency droop, recombination losses, "green gap", current crowding, Stokes losses, etc. Materials factors capable of lowering the LED efficiency, like composition fluctuations in InGaN alloys and plastic stress relaxation in device heterostructures, are also considered. Possible room for the efficiency improvement is discussed along with advanced schemes of color mixing and LED parameters optimal for generation of high-quality white light. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.


Karpov S.Yu.,Soft Impact Ltd.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2010

A simple model for estimation of spontaneous polarization in III-nitride compounds is suggested, utilizing the data on the materials lattice constants normally measured with sufficient accuracy. The model is applied to reconsider the spontaneous polarization in AlN, GaN, InN, and their alloys. The results are compared with those obtained by ab initio simulations. Polarization charges at the Al-GaN/GaN and InGaN/GaN interfaces are calculated and compared with available data. The model can be easily extended to other wurtzite compounds and their alloys. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

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