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.

This paper focuses on the specific features of an Ohmic contact on undoped n-InAs (n = 2 x 1016 cm-3) that could be used for temperature stabilization and/or temperature reduction in electronic devices, mainly operating in the 3-5 mu m mid-IR range. This feature has been demonstrated in a 100 mu m thick n-InAs slab with three unannealed Cr-Au-Ni-Au contacts formed via evaporation in vacuum. The I-V characteristics showed no deviation from Ohm's law in the temperature range 77-340 K, manifesting a contact resistance ranging from 3.6 x 10-5 to 7.2 x 10-5 Omega cm2 at room temperature. The 2D thermal radiation distribution and the temperature distribution over the n-InAs surface opposite the contact side surface was obtained via a pre-calibrated IR microscope operating at a wavelength of 3 mu m. The measurements revealed a current dependent temperature decline in the area adjacent to the negatively biased contact: at the applied power of 5 mW, cooling as strong as Delta T approximate to 1 K occurred at an ambient temperature of 340 K. The results show potential for the fabrication of heterostructures with a "built-in" cooler that is monolithically integrated with another electronic device.

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.

In this study, the individual components of thermal resistance in a AlInGaN laser were experimentally analyzed. The thermal resistance was measured using two approaches: an indirect method, based on the measurement of transient temperature-sensitive characteristics (the voltage at the p-n junction) with the T3Ster device, and a direct method using an infrared thermal imaging microscope.

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 is the same as for 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.

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.

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.

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.

Uncooled bridge photodetectors based on InAs/InAsSbP heterostructures for the mid-IR region of the spectrum are presented. The bridge structure is distinguished by the fact that the contact pad is placed outside the photosensitive mesa and is connected to it only by an air bridge contact. This design makes it possible to reduce the area of the p–n junction and the capacitance of the device, which leads to an increase in speed without loss of detectivity. The InAs/InAsSbP heterostructures were grown by vapor-phase epitaxy on InAs substrates with (111) orientation. The developed photodetectors have maximum spectral sensitivity in the range of 2.8–3.1 μm and differential resistance at zero shift R0 = 1.0–5.6 kΩ. The capacitance of the best devices is C = 3.4–3.6 pF at Urev = 0 V. The speed of the photodetectors was studied with an InGaAsP/InP laser with emission wavelength of 1.55 μm. The response time determined from the leading edge of the photoresponse is 200 ps. The created bridge photodetectors can be used to detect laser pulses in the range of 1.1–3.8 μm.

The paper presents temperature distribution analysis in activated on-chip chemical sensor based on p-InAsSbP/n-InAsSb/n-InAs 1x3 diode array. Temperature distributions were obtained both experimentally with the use of infrared microscopy, by I-V characteristic analysis and by finite element modelling. The simulated temperature values are in reasonable agreement with experimental data, allowing one to establish a relationship between the temperature of active elements of the sensor. The relationship is important for the improvement of chemical analysis accuracy.

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.

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.