Chaotic motion of 3U Cubesat with deployable side panels

The attitude motion of a small satellite with deployable side panels designed for passive aerodynamic stabilization in a rarefied atmosphere is considered. The influence of the aerodynamic and gravitational torques on the motion near the unstable and stable equilibrium positions at altitudes of 300–650 km is studied. The presence of the unstable equilibrium position and flexible elements is the cause of chaos. The equations of planar motion of the satellite with deployed flexible panels are obtained. A relationship between the satellite parameters is found, determining the range of altitudes in which the chaos is possible. The results of this paper can be used to assess the limits of applicability of passive aerodynamic stabilization for small satellites with deployable side panels.This study was supported by the Russian Foundation for Basic Research (RFBR 18-01-00215-A)

The use of short-period InGaN/GaN superlattices in blue-region light-emitting diodes

International audienceOptical and light-emitting diode structures with an active InGaN region containing short-period InGaN/GaN superlattices are studied. It is shown that short-period superlattices are thin two-dimensional layers with a relatively low In content that contain inclusions with a high In content 1–3 nm thick. Inclusions manifest themselves from the point of view of optical properties as a nonuniform array of quantum dots involved in a residual quantum well. The use of short-period superlattices in light-emitting diode structures allows one to decrease the concentration of nonradiative centers, as well as to increase the injection of carriers in the active region due to an increase in the effective height of the AlGaN barrier, which in general leads to an increase in the quantum efficiency of light-emitting diodes

Effect of stimulated phase separation on properties of blue, green and monolithic white LEDs

International audienceDifferent methods of stimulation of phase separation in an InGaN QWs by technological methods and by design of structure were investigated. Effect of admixing of hydrogen during growth interruptions (GIs) after deposition of the InGaN QWs on their structural and optical properties and properties of InGaN‐based LEDs was investigated. Effect of growth pressure on the phase separation was investigated and formation of separate InGaN islands at increase in growth pressure was revealed. It was shown that the phase separation is stumulated in composite InAlN/GaN/InGaN heterostructures and formation of well isolated InGaN islands was observed. Effect of the phase separation on the properties of the blue and deep green LEDs was investigated and strong changes in the spectral position and current dependence of the quantum efficiency were revealed. It was shown that formation of the island due to the phase separation allows control position and width of the emission line and maximum in current dependence of the quantum efficiency. Monolithic white LEDs are containing in active region blue and green InGaN QWs grown with applying of the GIs and emitting in spectral range from 440 nm to 560 nm were studied. Monolithic white LEDs having optimal design of active region demonstrate CCT in the range of 9000‐12000 K and maximal external quantum efficiency up to 14 lm/W

Effect of strain relaxation on active-region formation in InGaN/(Al)GaN heterostructures for green LEDs

International audienceProcesses of active-region formation for green LEDs on the basis of multilayer strained InGaN/GaN nanoheterostructures have been studied. It is shown that the formation of structures of this kind is highly affected by elastic stress relaxation leading to a larger amount of indium incorporated into InGaN layers. For structures emitting in the blue spectral range, an increase in the number of quantum wells (QWs) from 1 to 10 does not lead to stress relaxation or to a shift of the emission wavelength, whereas for structures emitting in the green spectral range, raising the number of QWs from one to five causes a monotonic increase in the emission wavelength

Single quantum well deep-green LEDs with buried InGaN/GaN short-period superlattice

International audienceIn spite of the great progress in III-N technology, LEDs with wavelength >530 nm 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 560–530 nm range