В ходе одного из важнейших процессов круговорота углерода в биосфере – фотосинтеза, происходят не только фотохимические и биохимические реакции, но и изотопное фракционирование основных биогенов и других элементов. Условия минерального питания, факторы влаго- и теплообеспеченности, видовые и сортовые особенности, световые условия при фотосинтезе влияют не только на его интенсивность, но и определяют изотопный состав ряда метаболитов, в том числе в зависимости от специфики растений по типу фиксации углерода (C3-, C4-, CAM- пути), чем и обоснован выбор объектов исследования – пшеница яровая (Triticum aestivum L.), как классический представитель C3- пути фиксации углерода и амарант (Amaranthus hopochondriacus L.), как классический представитель C4- культуры. Исследование изотопного состава метаболитов в целом, и углерода метаболитов в особенности, позволяют раскрыть физические и физиолого-биохимические механизмы протекания важнейших процессов в растениях. В настоящее время наиболее развитыми методами являются радиоизотопные исследования и методы с использованием масс-спектрометрии стабильных изотопов, требующие особых условий работы и сложной подготовки такой как: общее разложение проб (твердофазное окисление), методы хроматографии и другие. Нами предложен и апробирован ранее метод метаболизацации растворимых метаболитов с использованием культуры Saccharomyces cerevisiae в качестве альтернативного для последующей изотопной масс-спектрометрии – биологический метод пробоподготовки. Данный метод показал свою применимость для подготовки растительных проб к изотопному анализу углерода, а отсутствие фоторецепторных систем позволяет использовать Saccharomyces cerevisiae для определения влияния спектрального состава света на изменение изотопного состава углерода метаболитов растения. Инкубирование дрожжей с растительной пробой в прозрачной камере дает возможность облучать фотосинтезирующие листья растений, переводить углеводы растения в углекислый газ и отбирать пробы для масс-спектрометрических исследований изотопного состава углерода одновременно в динамике, когда как метод твердофазного окисления не позволяет исследовать нативные пробы при изменении факторов внешней среды. В работе показано влияние световых условий на фракционирование изотопов углерода листьями растений с различным типом фотосинтеза. С применением биологического метода подготовки проб в условиях динамического измерения состава метаболических газов определены и оценены скорости изменения изотопного отношения углерода 13С/12С в зависимости от спектральных характеристик освещения. Выявлено более значительное обогащение изотопом 13С листьев растений пшеницы с С3-типом фотосинтеза при облучении синим светом и листьев амаранта с С4-типом фотосинтеза при воздействии красным светом по сравнению с другими областями спектра.

Three main reasons for a temperature increase in activated p-InAsSbP/n-InAs/n-InAsSbP and p-InAsSbP/n-InAsSb/n-InAs double heterostructures has been considered. Contribution of nonradiative Auger recombination, electron-phonon interaction and Joule heating to diode temperature increase in single element LEDs and flip-chip diode arrays (1×3) were evaluated at forward and reverse bias using data on spatial distribution of the mid-IR radiation intensity and current-voltage characteristics.

The current and temperature dependences of the electrical, power and spectral characteristics of high-power deep UV LEDs (λ≈ 270 nm) have been studied. The main parameters of LED (internal quantum efficiency and light extraction efficiency) which determine output power capacity of the UV LED are calculated using the ABC-model. The influence of current distribution, electrical losses and thermal resistance as factors limiting the energy possibilities were estimated.

The thermal characteristics of SiC/Si samples obtained by the method of coordinated substitution of atoms at different thicknesses of SiC have been experimentally investigated. It has been found that for SiC thicknesses less than 200 nm, the thermal resistance of SiC/Si is approximately equal to 2 K/W, which coincides with a pure silicon substrate. Such samples will perfectly remove heat from the light-emitting heterostructure grown on SiC/Si. With an increase in the thickness of SiC, the SiC film is detached, which leads to a loss of thermal contact between SiC and Si. The thermal resistance increases at the same time by more than two orders of magnitude. The ability to remove easily the opaque part of the substrate can form the basis of the technology for manufacturing flip-chip LED chips.

The current and temperature dependences of the electrical, power and spectral characteristics of high-power deep UV LEDs (λ≈ 270 nm) have been studied. The main parameters of LED (internal quantum efficiency and light extraction efficiency) which determine output power capacity of the UV LED are calculated using the ABC-model. The influence of current distribution, electrical losses and thermal resistance as factors limiting the energy possibilities were estimated.

The object of study in this work was the most advanced AlInGaN LEDs of the “UX:3” design with a distributed system of reflective contacts located on the back side of the emitting chip. The current dependences of the output optical power and emission spectral characteristics, including their distribution (mapping) over the emitting surface, in a wide range of operating currents up to ~ 30A have been studied. An analysis of the near-field emission by intensity and spectrum revealed a high uniformity of the current density distribution at all levels of excitation (no current crowding). Thus, the saturation of the optical power and the quantum efficiency droop are explained by purely internal factors, which are well described by the ABC-model.

The current dependences of the output optical power and emission spectral characteristics, including their distribution (mapping) over the emitting surface, of vertical AlInGaN LEDs in a wide range of operating currents up to ~ 70A have been studied. Analysis of the current dependence of the LED optical power and emission spectrum reveals that, starting from a certain level of excitation, it is incorrect to use the value of the average current density when interpreting the ìefficiency dropî. The effect of ìcurrent crowdingî around the contacts becomes the main factor in reducing internal quantum and light extraction efficiency, limiting the energy capabilities of the LED.

The thermal droop of external quantum efficiency (EQE) at maximum in blue InGaN/GaN LEDs at j < 10 A/cm2 is caused by increasing losses related to non-radiative recombination due to carrier tunneling with the assistance of phonons and traps, enhancing by a temperature growth up to 400 K. When a p-n junction opens at j > 40 A/cm2, the EQE droop under direct current and at pulse mode is due to the losses associated with non-equilibrium filling of the states related to lateral alloy non-uniformities in quantum wells situated outside of the depletion region by delocalized carriers as well as the losses due to the interactions between delocalized carriers and extended defects.

AbstractA 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 spatial distribution of equilibrium and nonequilibrium (including luminescent) IR (infrared) radiation in flip-chip photodiodes based on InAsSbP/InAs double heterostructures (λmax = 3.4 μm) is measured and analyzed; the structural features of the photodiodes, including the reflective properties of the ohmic contacts, are taken into account. Optical area enhancement due to multiple internal reflection in photodiodes with different geometric characteristics is estimated.

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

Показано, что взаимодействие протонов с энергией 1 MeV и дозами (0.5-2)·1014 cm-2 с транзисторными структурами с двумерным AlGaN/GaN-каналом (AlGaN/GaN-HEMT) сопровождается не только генерацией точечных дефектов, но и образованием локальных областей с разупорядоченным наноматериалом. Степень разупорядоченности наноматериала оценивалась количественно методами мультифрактального анализа. Увеличение степени разупорядоченности наноматериала, наиболее ярко проявляющееся при дозе протонов 2· 1014 cm-2, приводит к падению подвижности и электронной плотности в двумерном канале HEMT-структур в несколько раз. При этом на транзисторах наблюдается падение величины тока сток-исток и рост тока утечки затвора на порядок. В HEMT-структурах с повышенной разупорядоченностью наноматериала до воздействия протонов, облучение протонами, даже с дозой 1· 1014 cm-2, приводит к подавлению двумерной проводимости в канале и выходу из строя транзисторов.

In spite of the great progress in III-N technology, LEDs with wavelength >530nm still exhibit low efficiency compared to blue and short-wavelength-green LEDs. Here we report on significant improvement of deep-green LED properties by modifications of the structure design. The combination of InGaN/GaN superlattice followed by low-temperature GaN is the key element to increase the electroluminescence efficiency for deep-green LED. Various techniques were employed to clarify the correlation between structure properties, growth regimes and design. Modification of the defect structure of the GaN buffer by InGaN layers appears to be mostly responsible for the observed effect. LEDs processed and assembled in a standard flip-chip geometry with Ni–Ag p-contact demonstrate external quantum efficiencies of 8–20% in the 560–530nm range.

We present L-I, I-V and spectral characteristics at 300 and 77 K of the flip-chip LED arrays based on p-InAsSbP/n-InGaAsSb heterostrucutres with photonic crystal formed onto an outcoupling n(+)-InAs substrate. We also describe results on IR imaging (2D radiation mapping) and near and far field patterns in forward biased LEDs.

We present L-I, I-V and spectral characteristics at 300 and 77 K of the flip-chip LED arrays based on p-InAsSbP/n- InGaAsSb heterostrucutres with photonic crystal formed onto an outcoupling n+-InAs substrate. We also describe results on IR imaging (2D radiation mapping) and near and far field patterns in forward biased LEDs.

Results obtained in studies of the near-field pattern of GaInAsSb IR flip-chip light-emitting diodes (LEDs) operating in the 2 μm range are presented. The electrical and reflective properties of ohmic contacts are discussed and the near-field emission distribution is analyzed in relation to the current and electrical and geometrical parameters of the LEDs.

InGaAsSb narrow gap heterostructures with p-InAsSbP claddings grown onto heavily doped n+-InAs substrates have been processed into 70 μm wide square mesas lined in a 1x4 array with individual addressing of elements. We report I-V, L-I characteristics of the array as well as IR images allowing characterization of cross talk, reflectance of the contacts and apparent temperatures in the spectral range around 3.6 μm. Reflectance and outcoupling efficiency is presented for photonics crystal structures with regard to their implementation in LED assemblies.

InGaAsSb narrow gap heterostructures with p-InAsSbP claddings grown onto heavily doped n+-InAs substrates have been processed into 70 mu m wide square mesas lined in a 1x4 array with individual addressing of elements. We report I-V, L-I characteristics of the array as well as IR images allowing characterization of cross talk, reflectance of the contacts and apparent temperatures in the spectral range around 3.6 mu m. Reflectance and outcoupling efficiency is presented for photonics crystal structures with regard to their implementation in LED assemblies.