The article investigates the temperature dependences of the current-voltage characteristics and reverse recovery of high-voltage AlxGa1- x As and AlxGa1- x As1- y Sb-y p-i-n diodes manufactured by liquid-phase epitaxy when heated to 350 degrees C. It was found that with an increase in the Al content in the base layers, the operating temperatures of the diodes increase from 250 degrees C at x = 0 to 350 degrees C at x similar to 0.45, while the forward voltage drops of the diodes also increase. It is shown that the use of small Sb additions in AlGaAs layers reduces the reverse recovery times of diodes by almost an order of magnitude, from 40-80 ns to 5-8 ns.

The energy and spectral characteristics of the most powerful AlInGaN LEDs with emission spectrum peaks at wavelengths of 440, 470, and 510 nm were studied in relation to the pumping of two laser media: Ti:Sapphire (Ti:Al2O3) and alexandrite (Cr:Al2BeO4). The absorption coefficients of the LED radiation in the laser media were studied experimentally with respect to the peak wavelength, operating mode, and excitation level. The corresponding spectral matching values (the efficiency of absorption of the pump radiation) were calculated for various combinations of the LEDs and active laser media. The energy characteristics (radiation power, pulse energy) of the LED emitters were studied over a wide range of excitation levels. The maximum energy capabilities of the LED emitters were assessed in terms of both output optical power and efficiency. The optimum combinations of LEDs and active laser media to achieve laser generation were determined.

A decrease in external quantum efficiency (EQE) of commercial LEDs based on MQW InGaN/GaN at wavelengths of 445, 530 and MQW AlGaN/GaN at 280 nm was experimentally studied in the standard aging mode at direct current. The decrease in EQE (regardless of the radiation wavelength) is found out to occur due to cooperative phenomena developing in 1–2 quantum wells (QWs) located in the space charge region (SCR) around the p–n junction, as well as in most of the QWs outside of SCR. It is shown that the inhomogeneous flow of current in these regions leads not only to the transformation of defects localized at heteroboundaries in the SCR and in lateral inhomogeneities in the alloy composition outside of SCR as well as in the extended defects, but also to a change in the alloy composition.

High-power AlGaInN LEDs are of interest for pumping of dyes lasers. In this regard, comprehensive studies of the power and spectral characteristics of LEDs in short-pulse modes used to laser pump were carried out. The energy capabilities and spectral properties of LED excitation of coumarin dyes were revealed.

The zone fluctuation potentials (ZFPs) in quantum wells located in the space charge region (SCR) of the p–n junction and the lateral ZFPs in quantum wells outside the SCR in blue, green, and UV LEDs based on nitrides have been experimentally determined. Green LEDs were used as an example to show that the low external quantum efficiency (EQE) of LEDs at the maximum correlated with an increase in the ZFP and disordering of heteroboundaries in quantum wells located in the SCR. The EQE at the maximum decreased because charge carriers were captured by charged centers localized at disordered heteroboundaries. The lateral ZFP in quantum wells located outside the SCR was the main parameter determining the decrease of the EQE from the moment the p–n junction opened until current densities reached 30–40 A/cm2.

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 have been calculated using the ABC-model. The influence of current distribution, electrical losses and thermal resistance as factors limiting the energy capabilities was estimated. Keywords: AlGaN, UV LED, quantum efficiency, light extraction efficiency, temperature dependence, ABC-model.

The main goal of this work was to study the energy characteristics of deep ultravi-olet light-emitting diodes and to establish the physical reasons for the limiting of output optical power and conversion efficiency of such devices. The voltage-current, light-current and spec-tral characteristics of the AlGaN multiquantum wells flip-chip light-emitting diodes emitting at a wavelength of 270 nm were experimentally studied in a wide range of operating current densities of 0.01-2.5 kA/cm2 and ambient temperatures of 200-350 K. Using the ABC-model, it was found that at a relatively high internal quantum efficiency of radiation of-70-90% and a quite acceptable value of series resistance of-1 & omega;. The main factor (key obstacle) limiting the energy possibilities of devices is low light extraction efficiency. The latter is due to the strong absorption of the generated light in the chip volume and on the contacts, as well as total internal reflection on the AlGaN/sapphire and sapphire/air interfaces.

A prominent source of charge carrier losses due to non-radiative recombination in AlGaN QWs, caused by the presence of charged centers localized at disordered hetero in-terfaces, has been experimentally revealed. It was found out that the spectral density of current low-frequency noise, which carries integral information about single defects and a defect sys-tem, is an order of magnitude higher in AlGaN QWs than in effective blue InGaN/GaN QWs. Thus, non-radiative recombination losses are still the source responsible for the low quantum efficiency of ultraviolet LEDs.

Data is reported on study of light-current characteristics and thermal properties of flip-chip AlGaN UV-C LED over a wide range of excitation levels: up to 2 kA/cm(2) in pulse mode. The tailor-made microscope based on InAs matrix with photosensitivity in 2.5-3.1 mu m range was employed for getting IR-intensity maps and revealing of temperature distribution across the emitting chips. The work is aimed at detailed study the factors limiting the energy capabilities of UV-C LEDs.

The contribution of several mechanisms into the external quantum efficiency (EQE) droop in green InGaN/GaN LEDs over a temperature increase from 300 to 400 K is clarified. One of them is the ionization of atoms localized at disordered hetero-interfaces in InGaN/GaN MQWs situated at the depletion region around a p-n junction at j < 10 A/cm2 and U < Utr (turn on voltage). The ionized atoms capture tunneling charge carriers, which leads to EQE decrease. Another mechanism is the capture of charge carriers tunneling in 3D spaces of MQWs situated outside of a depletion region at U > Utr and 10 A/cm2 < j < 30 A/cm2. Grow-ing thermalized carriers concentration reduces the band fluctuation potential which results in vertical diffusion transport of carriers and crowding effect.

Colloidal photonic crystals (CPCs) are universal ordered structures widely used in chemistry, physics, materials science, nanotechnology, and other fields of science and technology. In these materials, periodic alternation of elements with different refractive indices leads to the appearance of the so-called photonic bandgap and, as a consequence, to structural coloration. One-dimensional CPCs, also known as distributed Bragg reflectors or Bragg stacks, are used as cavities for distributed feedback lasers, smart dielectric layers, light-emitting transistors, induced tunable filters, etc. This review is concerned with recent advances in the 2D and 3D adaptive design of CPCs. In particular, methods are discussed for changing the morphology and thus the optical properties of CPCs, as well as the most widely used technologies for fabrication of CPCs. In addition, certain approaches used to achieve active tuning of the photonic bandgap are described.

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.

High-power AlGaInN LEDs are of interest for pumping of Ti-sapphire lasers. In this regard, comprehensive studies of the power and spectral’ characteristics of LEDs in short-pulse modes used to laser pump were carried out. The energy capabilities and spectral properties of LED excitation of Ti-Sapphire were revealed. Designs of LED arrays and a laser head have been developed, the distribution of pumping in the active element have been simulated.

The electroluminescent characteristics of powerful AlInGaN LEDs in the regime of high-pulsed current are investigated. The current dependencies of power and emission spectra of blue-green LEDs are established in their relationship with the efficiency of active medium Ti:Sapphire pumping. The reached values of the optical pumping power density using LEDs are estimated.

Comprehensive analysis of current spreading, temperature distribution and near field electroluminescence of high-power "UX:3" AlInGaN emitting chips with a distributed system of reflective contacts, located on the back of the chip, has been performed by combination of different experimental methods. Current dependences of power and spectral characteristics, including their distribution (mapping) over the emitting surface, were studied in a wide range of operating currents. A thermal resistance evaluation was based on transient electrical processes under heating by direct current and analysis of thermal equivalent circuit (the Cauer's model). The high resolution mapping of electroluminance and thermal radiation was obtained by optical microscope and infrared images technique. It has been established distribution pattern of light and temperature at different levels of excitation. The conclusions were drawn about the degree of uniformity of the current and light spreading and their influence on the power characteristics of devices.

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 ~ 30 A 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. Keywords: AlInGaN LED, quantum efficiency, emission spectrum, near-field emission.

The AlInGaN LEDs of the UX:3 design with a distributed system of reflective contacts located on the emitting crystal back, which are most advanced to date, are studied. The current dependences of power and spectral characteristics including their mapping over the radiating surface in a wide range of operating currents up to ~30 A have been investigated. Analysis of the radiation near-field according to intensity and spectrum has revealed a high uniformity of the current density at all levels of excitation (no crowding effect). The optical power saturation and the drop in quantum efficiency have been explained using only internal factors, which are well described by the ABC model.

The obtained experimental results allow us to clarify the nature of mechanisms related to the presence of cations in disordered InGaN alloy and hetero-interfaces. The capture of charge carriers by cations reduces the external quantum efficiency (EQE) in green MQWs at j < 10 A/cm2. The EQE droop phenomenon caused by smoothed out lateral potential fluctuations occurs at j > 10 A/cm2. At j > 40 A/cm2 the droop associated with interactions between charge carriers and dislocations and grain boundaries takes place.