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 (1x3) were evaluated at forward and reverse bias using data on spatial distribution of the mid-IR radiation intensity and current-voltage characteristics. Keywords: IR LED, IR diode array, Joule heating, Auger recombination, electron-phonon interaction.

This paper examines the thermal resistance of the mid-infrared “flip-chip” LEDs based on the p‑InAsSbP/n-InAsSb heterostructure. It was shown that the measurement of thermal resistance via a thermal control unit (forward p–n junction voltage) for LEDs based on narrow-gap semiconductors must be carried out at low temperature when thermal control unit is constant.

We study recombination processes in nitride LEDs emitting from 270 to 540 nm with EQE ranging from 4% to 70%. We found a significant correlation between the LEDs' electro-optical properties and the degree of nanomaterial disorder (DND) in quantum wells (QWs) and heterointerfaces. DND depends on the nanoarrangement of domain structure, random alloy fluctuations, and the presence of local regions with disrupted alloy stoichiometry. The decrease in EQE values is attributed to increased DND and excited defect (ED) concentrations, which can exceed those of Shockley-Read-Hall defects. We identify two mechanisms of interaction between EDs and charge carriers that lead to a narrowing or broadening of electroluminescence spectra and increase or decrease EQE, respectively. Both mechanisms involve multiphonon carrier capture and ionization, impacting EQE reduction and efficiency droop. The losses caused by these mechanisms directly affect EQE dependencies on current density and the maximum EQE values for LEDs, regardless of the emission wavelength. Another manifestation of these mechanisms is the reversibility of LED degradation. Recombination processes vary depending on whether QWs are within or outside the space charge region of the p-n junction.

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.

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.

Point defects were controllably introduced into 270 nm AlGaN Light-Emitting Diodes (LEDs) by 5 MeV electron and 1.1 MeV proton irradiations to examine the effect on electrical and luminescent characteristics. The 5 MeV electron irradiations had only a marginal effect on the charge distribution, current flow, and electroluminescence of LEDs for electron fluences up to 4.5 × 1016 e/cm2 that cause very strong degradation in green, blue, and near-UV LEDs. This lack of changes is attributed to the much higher charge densities in quantum-wells (QWs) and quantum barriers (QBs) of the 270 nm LEDs and to higher bond strength in high Al mole fraction AlGaN layers. By contrast, irradiation with 1.1 MeV protons with a fluence of 1016 p/cm2 leads to more than two orders of magnitude decrease in charge density in the QWs and QBs, a strong increase in the series resistance, and the emergence of deep electron traps near Ec-0.5 eV. The difference is explained by a much higher density of primary defects produced by protons. The observed effects are compared to changes in performance caused by aging after high driving current.

The work is devoted to the creation and study of high-power AlGaInN LED source with emission wavelengths (460–480) nm for pumping of solid-state lasers. The electrical, spectral, power and thermal characteristics were studied in a wide range of currents, continuous and pulsed modes. The design of LED matrices, which provides a tight “packing” of LEDs, their electrical commutation, efficient heat removal and a power supply for a wide pulse range has been proposed. The developed emitter comprises the most powerful and efficient to date LE Q8W (Osram) LEDs and is intended primarily for pumping Ti:Sapphire laser, the absorption band of which is well matched with the emission spectrum of the used LEDs. The achieved optical pumping power density in the pulsed mode is ~25 W/mm2, which corresponds to the lasing threshold.

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 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.

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.

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.

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 design and operation of a small-sized LED-based device for psychophysiological express diagnostics of functional states is considered. Diagnostics of functional states is carried out using dihaploscopic techniques for measuring the critical frequency of flicker fusion. The construction of the device includes a tablet computer with software for select, conFigure and run tests and a virtual reality glasses with LED matrix forming the color and shape of the test signal.

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.