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Saint Petersburg, Russia

Karpov S.,STR Group Soft Impact Ltd.
Proceedings of the International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD | Year: 2014

The paper reviews applications of ABC-model to interpret internal quantum efficiency and its droop in III-nitride light-emitting diodes (LEDs). Advantages of the model, its intrinsic limitations, and tentative mechanisms responsible for deviation of the model predictions from available observations are discussed. New experimental information on recombination processes in the LED active regions coming from the ABC-model is considered along with still open questions and tasks for further experimental and theoretical research. © 2014 IEEE. Source


Durnev M.V.,RAS Ioffe Physical - Technical Institute | Karpov S.Y.,STR Group Soft Impact Ltd.
Physica Status Solidi (B) Basic Research | Year: 2013

The polarization degree and emission pattern anisotropy of light emitted from strained (0001)Al(In)GaN heterostructures are studied by modelling. The model considers accurately the nonparabolicity of heavy, light, and split-off hole bands, the relevant modification of their densities of states, as well as the optical matrix element dispersion in the k-space. Accounting for all the above factors provides good agreement of the theoretical predictions with the data reported for both bulk AlGaN alloys grown on sapphire substrates and UV LED structures with Al(In)GaN quantum wells serving as the active regions of the devices. The band-structure modification in Al(In)GaN materials under variation of their composition and elastic strain are found to be the primary factors controlling the polarization degree and emission patterns of TE- and TM-polarized light. The anisotropy of the TM-polarized emission pattern (dependence of the emission intensity on the direction of photon release) and polarization degree of the emitted light are found to be remarkably influenced by the nonparabolicity of the hole bands. Comparison of the experimental polarization degrees (symbols) with the theoretical ones (lines) calculated for different in-plane strains in light-emitting Al(In)GaN heterostructures. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Karpov S.,STR Group Soft Impact Ltd.
Optical and Quantum Electronics | Year: 2015

The paper reviews applications of ABC-model to interpret internal quantum efficiency and its droop in III-nitride light-emitting diodes. Advantages of the model, its intrinsic limitations, and tentative mechanisms responsible for deviation of the model predictions from available observations are discussed. New experimental information on recombination processes in the LED active regions coming in terms of the ABC-model is considered along with still open questions and tasks for further experimental and theoretical studies. © 2014, Springer Science+Business Media New York. Source


Karpov S.Y.,STR Group Soft Impact Ltd.
Physica Status Solidi - Rapid Research Letters | Year: 2010

A model is suggested accounting for effects of localized electron and hole states formed by composition fluctuations in the InGaN active region of a III-nitride LED on non-radiative carrier recombination at threading dislocations. The model enables explanation of the abnormal temperature dependence of internal quantum efficiency (IQE) of a green LED structure recently observed at low current densities. The theoretical predictions are in quantitative agreement with experiment in the temperature range between 200 K and 453 K. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Chernyakov A.E.,Russian Academy of Sciences | Bulashevich K.A.,STR Group Soft Impact Ltd. | Karpov S.Y.,STR Group Soft Impact Ltd. | Zakgeim A.L.,Russian Academy of Sciences
Physica Status Solidi (A) Applications and Materials Science | Year: 2013

Comprehensive analysis of current spreading, temperature distribution, and near-field electroluminescence (EL) of high-power flip-chip InGaN/GaN light-emitting diodes (LEDs) has been performed by combination of experimental and theoretical methods. High-resolution mapping of EL and thermal radiation was obtained by optical and infra-red (IR) microscopes. Thermal resistance of the chip was measured by forward-voltage relaxation technique. 3D coupled electrical, thermal, and optical simulations were carried out using hybrid 1D/3D model. The theoretical predictions agree well with available observations. The lateral distributions of the near-field EL intensity and temperature are found to be qualitatively similar to that of the current density but to have substantially lower degree of non-uniformity. Therefore, it becomes incorrect to judge the current crowding in the LED chip by the measured contrast of the EL image. The role of contact resistances in stabilization of the current spreading pattern is revealed by modeling. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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