Efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes with nonuniform current spreading

We demonstrate that the efficiency droop phenomenon in multiple quantum well InGaN/GaN light-emitting diodes (LEDs) may be connected to the current crowding effect. A numerical model of internal quantum efficiency calculation is presented that takes into account nonuniform lateral carrier injection in the active region. Based on this model, we examine the effect of current crowding on the efficiency droop using comparison of simulated internal quantum efficiency of InGaN LEDs with low and high uniformity of current spreading. The results of simulations and measurements show that the devices with low uniformity of current spreading exhibit higher efficiency droop and lower roll-off current value

Technique and setup for diagnostics of p-n junction–package thermal resistance in high-power gallium nitride LEDs

We present a setup and procedure of studying p-n junction–package thermal resistance in high-power light-emitting diodes (LEDs) from their thermal relaxation. A set of LEDs mounted on a metal-core printed circuit board (MCPCB) were studied. The contributions to the total thermal resistance from a heavy heat sink, MCPCB, heat slug and LED chip are separated

The Effect of Current Crowding on the Internal Quantum Efficiency of InAsSb/InAs Light-Emitting Diodes

The effect of current crowding on the internal quantum efficiency (IQE) of InAsSb/InAs light- emitting diodes (LEDs) operating in the middle�infrared (mid�IR) range (λ = 3–5 μm) has been studied. Calculations based on a modified model of recombination coefficients show that current crowding leads to a significant decrease in the IQE of LEDs, which is especially pronounced in longer�wavelength devices (23% at λ = 3.4 μm versus 39% at λ = 4.2 μm). The obtained results indicate that the effect of current crowding should be taken into consideration as an additional nonthermal mechanism of IQE decrease in mid-IR LEDs

Temperature dependence of contact resistance of Au-Ti-Pd2Si-n+-Si ohmic contacts

We investigated temperature dependence of contact resistance of an Au-Ti-Pd2Si ohmic contact to heavily doped n+-Si. The contact resistance increases with temperature owing to conduction through the metal shunts. In this case, the limiting process is diffusion input of electrons to the metal shunts. The proposed mechanism of contact resistance formation seems to realize also in the case of wide-gap semiconductors with high concentration of surface states and dislocation density in the contact

Temperature-dependent efficiency droop in InGaN-based light-emitting diodes induced by current crowding

Temperature-dependent internal quantum efficiency (IQE) of multiple quantum well InGaN/GaN light-emitting diodes (LEDs) has been investigated. IQE versus current relation is analysed using the modified rate equation model that takes into account the current crowding effect at different temperatures. The results of calculations are consistent with the fact that droop in IQE at higher currents originates from Auger recombination increased by current crowding. It is shown that unusual experimentally observed temperature dependence of the efficiency droop can be explained by stronger lateral nonuniformity of carrier injection at low temperatures without any assumptions about carrier delocalization from In-rich regions in quantum wells

Pedagogical interaction in the context of humanization of education

The article deals with the problem of pedagogical interaction, its potential in educational and upbringing processes directed to humanization of relations between teacher and pupils. On the basis of analysis of the research it can be concluded that pedagogical science operates with a conception of pedagogical interaction, that is considered to be one of the principal categories of pedagogics. It has to be emphasized thatthe conception “interaction” in general understanding reflects the universal general form of movement and influence of objects at each other. For man it is their characteristic aspiration in the interaction with different objects of the surrounding world. Through the interaction men learns about natural and social phenomena, conform to law, processes and determine the methods of their thinking andbehaviour. Men’s need in communication, studying, education and his own development are connected with this concept

Природоохоронні об’єкти Волинської області, як об’єкти туризму

Природоохоронні об’єкти Волинської області вагома складова туристичної галузі регіону

ПІДВИЩЕННЯ БІОРІЗНОМАНІТТЯ РОСЛИННИХ ФОРМАЦІЙ ПІД ЧАС ЗЕМЛЕУСТРОЮ АГРОЛАНДШАФТУ

The authors analyse current international literary sources addressing the issues of increasing biodiversity. We have found that restoring agricultural ecosystem stability by means of reducing plough disturbance in the area and increasing biodiversity results in climate change mitigation by creating agricultural landscapes that are similar to natural landscapes. The studies have been conducted within land use area located within the jurisdiction of Velyka Khaicha Village Council in Ovruch District, Zhytomyr Oblast, which lies on the Slovechansk-Ovruch Ridge. The studied area varies in its relief, topsoil and waterlogging level. The land use area contains slopes ranging from 3 о to 11 о. Grey forest soils affected by varying degrees of erosion predominate on the area with a complex relief, whereas deluvial sediments, calcareous gley and soddy low-podzol gley soils prevail in waterlogged areas. Eroded land area equals 765.7 ha, while waterlogged and boggy land area equals 365.8 ha. The agroecological state of the topsoil in the studied area has been analysed in terms of soil erosion class and waterlogging intensity. Soil erosion class and certain biological properties of plant species, such as root system branching, projected soil surface coverage by plant tops, as well as spring regrowth times, have been taken into account when developing grass mixtures for grassland restoration on slopes. Plant sensitivity to growing in waterlogged or boggy areas has been taken into account during hay meadow management. The allelopathic properties of plant species have also been taken into account when forming plant aggregations. A grass mixture consisting primarily of such gramineous plants as Festuka pratensis, Poa pratensis, Dactylis glomerata, Loliym perrene, as well as such leguminous plants as Trifolium pratensis, Medicago media, Оnobrychis arenaria, Gotus corhiculatus, has been developed for grassland restoration on slopes. The ratio of gramineous plants in the grass mixture for hay meadow management is even higher; leguminous plants in this grass mixture include Trifolium pratensis and Medicago falkata. Through a comparison of agroecological properties of the topsoil and biological properties of perennial plants it has been established that the ratio of perennial plant species for grassland restoration on slopes in the optimal grass mixture for grey and light-grey podzolised soils within the studied agricultural landscape equals 25 % of leguminous plants and 75 % of gramineous plants, and in the grass mixture for hay meadow creation on gley soils, 15 % and 85 %, respectively.Проаналізовано сучасні світові літературні джерела, що висвітлюють питання підвищення біорізноманіття агроландшафтів. Встановлено, що питання є актуальним, оскільки підтримання різноманітності видів живих елементів екосистеми є обов'язковим для формування стійких територій. Зроблено висновок, що світові дослідження доводять – відновлення стійкості агроекосистем шляхом зменшення розораності території та збільшення біорізноманіття веде до пом'якшення наслідків зміни клімату шляхом створення агроландшафтів, близьких до природних. Дослідження проведено на площі землекористування в межах Великохайчанської сільської ради Овруцького району Житомирської області, що розташована на території Словечансько-Овруцького кряжу. Встановлено, що досліджувана територія різноманітна за рельєфом, ґрунтовим покривом та рівнем перезволоження. Під час формування травосумішей для залуження схилів враховано ступінь еродованості ґрунтів та біологічні особливості рослин. Під час облаштування сіножаті враховано чутливість рослин до зростання на перезволожених або заболочених територіях. На основі зіставлення агроекологічних властивостей ґрунтового покриву і біологічних особливостей багаторічних трав встановлено, що для сірих та ясно-сірих опідзолених ґрунтів досліджуваного агроландшафту найпридатнішою є травосуміш, в якій питома вага багаторічних трав для залуження схилів становить: бобових – 25 %, злакових – 75 %. Для створення сіножаті на глейових ґрунтах відповідно – 15 і 85 %