Development of modeling methods and algorithm for calculating the current-voltage characteristics of LED modules

Current-voltage characteristics of real high-power LED chips and their defects were studied. Process of modeling LED matrix by using Monte Carlo method based on the measured real LED chips was considered and performed. It was shown that the risk of variating LED chip parameters for stability of a final LED matrix as a result of the non-uniform heating up of individual elements in a series-parallel circuit. The solution allowing to significantly reducing the influence of LED chips input parameters variationon the final parameters of LED matrix was proposed

Effect of neutron irradiation on non-equilibrium HfB₂-B₄C composites

We studied the effect of neutron irradiation on composite material HfC-HfB₂- C made using rapid reactive hot pressing technology. The histograms of microhardness and results of X-ray phase analysis, obtained both before and after neutron and electron irradiation of the samples, were considered. It was found that secondary electrons make a considerable contribution at low-fluence (~10¹⁴ neutron/cm² ) neutron irradiation. Afluence range was determined at which reduction of composite material microhardness is observed

Hybrid-integrated version of SBD amplitude detector intended for the 400–600 GHz frequency range

A finline version of detector with flat Schottky barrier diodes is developed. It is intended for operation in the 400600 GHz frequency range. The detector electrical parameters are studied. The detector conversion ratio at a frequency of 420 GHz is 97 V/W

Hybrid-integrated version of solid-state components for terahertz frequency region

We present the results of development of key components for THz devices obtained using mathematical modeling of detector sections, radiation source and subharmonic mixers. Schottky barrier diodes with different parameters served as nonlinear elements of the above facilities

Determination of the Schottky barrier height in diodes based on Au–TiB₂–n-SiC 6H from the current-voltage and capacitance-voltage characteristics

We present the results of investigation of the barrier height and ideality factor in Schottky barrier diodes based on Au–TiB₂–n-SiC 6H relying on measuring the current-voltage and capacitance-voltage characteristics. Improving the accuracy of the methods that take into account the effect of the series resistance in calculating the ideality factor and barrier height has been shown with the Cheung method and direct approximation one. It has been ascertained that an inconsistency between real currentvoltage characteristics and its model – the temperature dependence of the barrier height, the ideality factor dependence on the voltage – introduces the basic error into the calculated parameters in the diode under study

Degradation processes in LED modules

Electrical-heat-light degradation model of a light-emitting module has been developed in this work. The Monte-Carlo method was used to calculate the reliability time of LED modules with different halfwidth of LED chip series resistance. Separation of LED chips with different series resistance before assembling may increase the time of emission in a stable mode up to 10%

Вплив зовнішніх дій на механічні напруження і електронні параметри гетеросистем з С60 фулеренами

The results of a complex study of C60/Si heterosystems are presented in this work: the crystal structure and composition of the films, internal mechanical stresses, electronic parameters of the film and the film-substrate interface, and the effect of external influences (ultraviolet irradiation, thermal annealing, gamma and microwave irradiation). The advantage of microwave treatment over others is established: the absence of fullerene decomposition, the removal of internal mechanical stresses in the heterosystem, and the improvement of its electronic parameters. Methods for remove the decomposition of C60 molecules under the influence of other treatments have been developed. To eliminate the interaction of fullerenes with oxygen, it was proposed to perform thermal annealing and UV irradiation in vacuum, and in the case of g-irradiation, apply a protective coating on the surface of the film (GeOx or SiOx). In solar cells with C6 films in the polymer matrix on Si, a significant advantage of titanium contacts in comparison with gold is established, especially after microwave treatment. Contact resistance decreased as a result of hybridization of 3d-orbitals of titanium and 2p-orbitals of fullerenes with the formation of ТіхС60 carbides and radiation-stimulated diffusion of metals, which increases the contact area.В роботі приведені результати комплексного дослідження гетеросистем С60/Si: кристалічної структури і складу плівок, внутрішніх механічних напружень, електронних параметрів плівки і межі поділу плівка-підкладка та впливу на них зовнішніх дій (ультрафіолетового опромінення, термічного відпалу, гамма та мікрохвильового опромінення). Встановлено перевагу мікрохвильової обробки перед іншими: відсутність розпаду фулеренів, повне усунення внутрішніх механічних напружень в гетеросистемі та покращення її електронних параметрів. Розроблені методи усунення розвалу молекул С60 під дією інших обробок. Термічний відпал і УФ-опромінення пропонується проводити у вакуумі, а для g-опромінення наносити захисне покриття на поверхню плівки (GeOx або SiOx) для усунення взаємодії фулеренів з киснем. В сонячних комірках з плівками С60 в полімерній матриці на Si встановлена суттєва перевага титанових контактів перед золотими, особливо після мікрохвильової обробки. Контактний опір зменшувався в результаті гібридизації 3d-орбіталей титану і 2р-орбіталей фулеренів з утворенням карбідів ТіхС60 та радіаційно-стимульованої дифузії металів, яка збільшує площу контакту

Formation of ohmic contacts to n(p)-gan and measurement of their contact resistivity

We propose multilayer ohmic contacts to n- and p-GaN layers, with titanium boride as diffusion barrier. It is shown that the optimal method of contact resistivity measurement is the transmission line method (TLM) with circular contact geometry. The Ti−Al−TiBx−Au contact metallization to n-GaN retains its layer structure after thermal annealing at temperatures up to 900 °C. The contact resistivity ρс is (6.69±1.67)×10⁻⁵ Ω⋅cm². For the Au−TiBx−Ni−p-GaN contact structure, the contact resistivity is (1±0.15)×10⁻³ Ω⋅cm²

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

We present a setup and procedure of studying p-n junction to case 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

Some aspects of thermal resistance measurement technique for IMPATT and light-emitting diodes

Some aspects of measuring the thermal resistance to a constant heat flow at a p-n junction–package region in IMPATT and light-emitting diodes are considered. We propose a method of studying the thermal resistance of high-power light-emitting diodes. This method makes it possible to increase accuracy of measuring the thermal resistance by determining the temperature at a linear section of the voltage−temperature curve. A possibility to measure the thermal resistance of IMPATT diodes by using the pulse I-V curves is shown. This enables one to simplify calculations and increase accuracy of measuring the thermal resistance