We study the formation of a superradiant optical mode in the room temperature reflection spectra from resonant Bragg structures (RBSs) composed of single and double (In,Ga)N quantum wells (QWs) in the unit cell. The appearance of the mode manifests itself by a significant increase in the resonant optical reflectivity due to the electromagnetic coupling of quasi-two-dimensional excitons in the QWs. The implementation of the supercells with double (In,Ga)N QWs results in an increase in the oscillator strength of the quasi-2D excitons and corresponding rise of the radiative broadening parameter to the value as high as 0.3 +/- 0.02 meV. We also show that the supercells with double QWs are preferable for RBS with large number of periods due to better tolerance to deviations from the exact periodicity.

We experimentally demonstrate the formation of a superradiant optical mode in the room-temperature reflection spectra from a resonant Bragg structure composed of 30 equidistant GaN quantum wells separated by (Al,Ga)N barriers. The mode arises when the condition of the Bragg diffraction is fulfilled at the wavelength corresponding to the energy of the quasi-two-dimensional excitons in the quantum wells. It manifests itself as a significant increase in the amplitude and a change in the shape of the resonant optical reflection due to the electromagnetic coupling of the excitons. By modeling of the optical spectra, we evaluate the radiative and non-radiative broadening parameters of the excitonic states in the GaN quantum wells, which appear to be 0.4 +/- 0.02 and 40 +/- 5 meV, correspondingly, for the resonant exciton energy of 3.605 eV. The resonant Bragg structure based on the periodic sequence of the GaN quantum wells demonstrates an efficient coupling of photons and excitons at room temperature, which makes it promising for device applications.

Room-temperature reflectance spectra are recorded for a resonant Bragg structure with 30 GaN/AlGaN quantum wells. Accurate quantitative fitting of the experimental results is achieve by means of transfer matrix numerical modeling. Parameters of radiative and nonradiative exciton broadening in the GaN/AlGaN quantum wells are determined.

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.

Epitaxial layers of Al x Ga 1-x As 1-y Sb y with an aluminum content x~60% and antimony content y~3% were successfully grown by molecular-beam epitaxy at low temperature. A developed system of AsSb nanoinclusions was formed in the semiconductor matrix by subsequent annealing. The extended transparency window of the obtained metamaterial allows us to document the absorption of light near the interband absorption edge of the Al x Ga 1-x As 1-y Sb y semiconductor matrix. Parameters of the observed extinction band allow us to attribute the optical absorption to the plasmon resonance in the system of AsSb nanoinclusions. Keywords: molecular beam epitaxy, x-ray diffraction analysis, transmission electron microscopy, optical properties, plasmon resonance.

The given work is devoted to studying the optical properties of the sample with of 30 GaN quantum wells separated by non-tunneling AlGaN barriers. Optical reflectance was studied at different angles of incidence for different polarization of the incident light at room temperature. A model has been verified that makes it possible to describe the experimental data and determine the parameters of excitons in quantum wells. This material system seems to be most promising for implementation of the concept into devices.

We studied an effect of spatial disorder on the optical response of resonant Bragg structures with InGaN quantum wells. Using an experimentally verified model, we calculated a transformation of the optical reflection from the resonant Bragg structures with 60, 100, and 200 quantum wells as a function of the degree of disorder in the system. A critical threshold deviation from the exact periodicity was revealed, which causes a qualitative change of the optical resonance.

Методом молекулярно-лучевой эпитаксии при низкой температуре с использованием прерываний роста успешно выращены эпитаксиальные слои Al x Ga 1-x As 1-y Sb y с содержанием алюминия x~60% и содержанием сурьмы y~3%. Путем последующего отжига в полупроводниковой матрице сформирована развитая система нановключений AsSb. Увеличенное окно прозрачности полученного метаматериала позволило надежно документировать широкую полосу поглощения света вблизи края межзонного поглощения полупроводниковой матрицы Al x Ga 1-x As 1-y Sb y . Параметры наблюдаемой полосы экстинкции позволяют связать такое поглощение света с плазмонным резонансом в системе нановключений AsSb. Ключевые слова: молекулярно-лучевая эпитаксия, рентгенодифракционный анализ, просвечивающая электронная микроскопия, оптические свойства, плазмонный резонанс.

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.

Reflection spectra from a resonant Bragg structure with 30 GaN/AlGaN quantum wells have been measured at room temperature. Numerical modeling using the method of transfer matrices gave a quantitatively accurate fit of the experimental results. Defined radiative and non-radiative broadening parameters of the exciton in GaN/AlGaN quantum wells.

The optical properties of a structure with a periodic system of 100 InGaN quantum wells separated by nontunneling GaN barriers are investigated at room temperature. The structure periodicity corresponds to the Bragg-diffraction condition at the quantum-well exciton frequency. The results of numerical simulation using transfer matrices are in reasonable quantitative agreement with the experimental data. The model includes the resonance response of A, B, and C excitons in the quantum wells and the optical absorption tail in the barrier and buffer layers. The radiative and nonradiative damping rates of excitons in the InGaN quantum wells are determined.

The goal of the study is examination of current-crowding effect in high power AlInGaN LEDs. This effect was presented by mapping of EL (electroluminescence) near filed under high pulse current. LED chip of vertical design was study in high range of current (10 −9 ÷ 70A). This operating mode of LEDs are interesting for different applications, such as pumping lasers, VLC and LiFi, as well as for investigation accelerated degradation process of LEDs.

LEDs operating under high pulsed current are of a great interest for different applications, in particular, for VLC (LiFi) systems and laser pumping. Current dependences of the efficiency and emission spectra as well as the rise and fall times of high-power blue LEDs were investigated under extremely high pulse current density up to 7 kA/cm2 and pulse duration from 100 ns to 3 μs. Analysis of the pulse behaviour of the LEDs reveals that the main droop in the efficiency and change in spectra occur up to the current densities ~ 1 kA/cm2 and seems to be non-thermal.

Optical properties of a structure with a periodic system of 100 InGaN quantum wells (QWs) separated by non-tunneling GaN barriers have been investigated at room temperature. The structure periodicity corresponded to the Bragg diffraction condition at the frequency of the QW excitons. Numerical modeling using transfer matrices gave a quantitatively accurate fit of the experimental results. The model included the resonance response of A, B, and C excitons in QWs and an optical absorption tail in the barriers and buffer layer. We have determined the radiative and non-radiative broadening of the excitons in the InGaN QWs.