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St.Petersburg, Russia

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. Source

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. Source

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. Source

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. Source

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. Source

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