Phone: þ7 812 292 7922, Fax: þ7 812 297 8640Comprehensive analysis of current spreading, temperature distribution, and near-field electroluminescence (EL) of highpower 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 forwardvoltage 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.

The degradation of blue light emitting diodes (LEDs) with different structural disorder based on MQW InGaN/GaN grown by MOCVD on sapphire has been investigated. New approach to analyze the degradation has been used. It takes into account the structural disorder determined by the extended defect system relaxation and related with poor coalescence of the mosaic structure domains. The results obtained leads to assumption that the migration and segregations of Ga on domain dislocation boundaries of the mosaic structure and the change of energy activation of Mg related centers are important reasons of degradation for all types of LEDs The fastest degradation for poor ordered LEDs was observed.

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Current-voltage characteristics and quantum efficiency dependence on injected current for blue light emitting diodes with different nanostructural arrangement were studied. The Electron Beam Induced Current (EBIC) technique was used to monitor the hole recombination inside the quantum wells and to reveal the lateral inhomogeneities in the recombination velocity. The bright EBIC contrast associated with extended defects was revealed. This contrast was explained by a formation of channels with enhanced conductivity near the extended defects penetrating the active device region. 1 Introduction In spite of essential progress in the multiple quantum well (MQW) InGaN/GaN blue light emitting diodes (LED) technology, the reasons for rather high values of external quantum efficiency (QE) at low injection currents and its decrease at injection currents larger than 100 mA are not clear yet. The major part of investigations in this field dealt with studies of radiation recombination efficiency dependence on the In inhomogeneous distribution into InGaN layers leading to a quantum dot formation, on the layer thickness variation in MQW InGaN/GaN structures, on the polarization field and on dislocation density. However, the extended defect system in III-nitrides besides the threading dislocations includes also the typical for these materials mosaic structure, ordering of which could depend essentially on the defect system relaxation. For the well-ordered mosaic structures the defect relaxation occurs via the coherent concordance of mosaic structure domains with a formation of dilatation boundaries, while for the less-ordered mosaic structures the defect system relaxation occurs via the formation of numerous dislocated domain boundaries, the edge dislocation density in which exceeds essentially that of screw threading dislocations [1]. As shown in [2,3], the close correlation between mosaic structure ordering and the surface roughness allows the quantitative characterization of mosaic structure ordering by the multifractal analysis based on the atomic force microscopy data. However, in spite of essential ordering effect on the electrical and optical properties of hexagonal III-nitrides, the detail study of QE dependence in the III-nitride based LEDs on the nanostructural arrangement (NA) determined by the extended defect system relaxation was not carried out up to now.In the present work a comparative study of LEDs with the different NA has been carried out. The main purpose of this study is revealing a correlation between the NA and the electroluminescence efficiency and current-voltage (I -V) characteristics. The Electron Beam Induced Current (EBIC) technique

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The results on surface control of light-emitting structures (LES) based on MQW InGaN/GaN grown by MOCVD on (0001) sapphire substrates have been presented. For these purposes, the treatment of atomicforce-microscopy data by multifractal analyses has been applied. It was shown, that multifractal parameter (the degree of order of mosaic structure, ∆) reflects the peculiarities of the extended defect system (EDS), including mosaic structure and high density of dislocations, and correlates with the volume structural, electrical and optical properties of LES. Depending on ∆, EDS relaxes with formation of either the domain dilatation boundaries or numerous domain dislocation boundaries and these structural peculiarities influence essentially the shape of photo-and electroluminescence spectra, delayed spectra and the values of external quantum efficency. The surface control using ∆ can be applied to optimize the properties of LES and the process of their creation.

Проведены измерения и анализ пространственного распределения равновесного и неравновесного (в том числе люминесцентного) излучения в средневолновых ИК флип-чип фотодиодах на основе двойных гетероструктур InAsSbP/InAs (lambdamax=3.4 мкм) с учетом конструктивных особенностей фотодиодов, включая отражательные свойства омических контактов. Сделана оценка увеличения оптической площади сбора фотонов за счет лучей, испытывающих многократные отражения внутри полупроводниковых чипов с различающимися геометрическими характеристиками. DOI: 10.21883/FTP.2017.02.44117.8380