Manufacturability of high power ultraviolet-C light emitting diodes on bulk aluminum nitride substrates
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Summary form only given: Bulk AlN substrates are an ideal solution for the growth of ultraviolet-C light emitting diodes (UVCLED). They are optically transparent at this wavelength and closely lattice and thermally expansion matched to the layers required for the device structure. In addition pseudomorphic growth can be achieved allowing for low dislocation density in the active region of the device. This approach has been used to achieve the best efficiency and output power, as well as lifetime, in the 265 nm wavelength range. However, currently these substrates are only available in limit quantities and sizes preventing large scale manufacturing such as is occurring with visible LEDs. Regardless, we have been able to succeed in setting up pilot production of UVCLEDs to enable low volume manufacturing and allow for rapid increase in volumes as supply and size of the AlN substrates are increased. This pilot production line utilizes the bulk substrate manufacturing and epitaxial growth at Crystal IS and the high volume fabrication facility at Sanan Optoelectronics. The current process uses 10 x 10 mm 2 AlN substrates. The epitaxial growth process as tracked using both non contact sheet resistance measurements and X-ray diffraction for analyzing the variation in aluminum content of the n type AlGaN layer of each wafer. The sheet resistance and Al content over several lots of wafers is shown. The sheet resistance shows a normal distribution with a mean of 341 ohms/sq. and dispersion of 89 ohms/sq. This value is desired to be as low as possible but in the current range is more than adequate for high performance UVCLEDs. The Al content is targeted at 70% with an upper specification limit (USL) of 75% and a lower specification limit (LSL) of 65%. The distribution is bimodal but does have a mean value of 70.0% and a dispersion of 2.2% indicating the Al% is well controlled with the specification limits. The fabrication process is similar to high volume production of visible LEDs but differs in several key areas. As fabrication facilities are moving beyond 2" substrates and relying on more sophisticated automation to improve yields, the processing of 10x10 mm 2 substrates presents challenges in wafer handling and processing. We have been successful in implementing the fabrication of these wafers in pilot production. By carefully tracking key process parameters such as etch depths, metal thickness, and contact resistances devices can be fabricated with optimal parameters. The output power measured on wafer after the fabrication process is shown. This output power is measured through the partially absorbing AlN substrate at 100 mA of input current and typically at an emission wavelength of 265 nm. This results in a mean output power over 1 mW. This value can be increased significantly once the device is packaged and we have currently demonstrated over an order of magnitude improvement by introducing enhanced photon extraction methods to the device. Additional parameters such as forward voltage and wavelength will be discussed.Keywords:
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Light-emitting diodes (LEDs) degradation during 10 000 hours and the influence of ultrasonic action on the InGaN LEDs were investigated. The model of LED degradation is suggested and based on 1) common LED is the combination of parallel Small-LEDs (S-LED) which correspond to the areas with different concentration of In atoms; 2) redistribution of In atoms in quantum-dimensional active region of blue InGaN LED under strong piezoelectric effect and spontaneous polarization induced by ultrasonics; 3) the ultrasonics which is used in creating LEDs can make defects in heterostructures and they (during LEDs work) are heated by current or ultrasonic, can be increased and that's why nonradiation recombination decreases LEDs efficiency. It can be said that great current density flows through areas with low In concentration and therefore S-LEDs are "burned out" and irradiate less. At the areas with average In concentration the densities decrease. That is why electroluminescence spectrum, radiation power, luminous intensity characteristics are shifted to the long wave region. All that also exactly corresponds with our experimental results of LEDs degradation investigation during 10 000 hours.
Wide-bandgap semiconductor
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Multi-channel light-emitting diode (LED) light sources have been developed for various applications in lighting, but especially for spectrum-tunable lighting. However, how to select the optimal combination of LEDs for these light sources is rarely discussed. Unlike the negative-pruning process which operates by removing LEDs from a set of available LEDs based on an unrealizable negative-coefficient criterion alone, the proposed pruning process removes LEDs so as to minimize the synthesis error. This method not only produces the same optimal set of LEDs as those identified by the full-search method but also suggests when using phosphor-converted LEDs is beneficial. It does this by investigating the trade-off between the full width half maximum of the LEDs and the number of LEDs.
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Light extraction in thin-film GaN light-emitting diodes (LEDs) prepared with Si substrates pretreated by surface roughening and imbedded electrodes were studied. The LEDs were fabricated with a roughened p-GaN layer, followed by epilayer transferring. There are four types of LEDs: conventional LEDs (C-LED), n-side-up thin GaN LEDs with imbedded electrodes and a KOH-roughened n-GaN (first-type LED), p-side-up thin GaN LEDs with a KOH-roughened n-GaN (second-type LED), and n-side-up thin GaN LEDs with imbedded electrodes and without KOH-roughened n-GaN (third-type LED). The electrical properties of the LEDs are almost the same. However, they differ in luminance intensity. The luminance intensities (at 350 mA) of C-LED, first-type, second-type, and third-type LEDs are 3468, 9105, 7610, and 7047 mcd, respectively. The brightest LED is first-type LED. This may be due to emission surface with pyramidal-textured surface and without light shading electrodes. They enhance the light extraction for first-type LEDs.
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국내 LEDs 산업의 발달함에 따라 LEDs 가격이 지속적으로 낮아지며 광량과 내구성이 좋은 LEDs가 개발되어 불량한 기후 조건에서 작물의 수량을 증진하기 위하여 시설재배 농가를 중심으로 원예작물에 LEDs 이용을 위한 시도가 이뤄지고 있다. 이에 본 실험은 적색과 초적색 LEDs 보광이 ``홍로``/M.26 사과의 과중분포 및 과실품질에 미치는 영향을 구명하여 사과에서 LEDs 보광이 과실의 품질향상에 도움이 될수 있는지를 구명하기 위하여 실험하였다. 실험 처리는 대조구인 무처리구, 적색광(660nm) 2, 4시간 조사구, 초적색광(730nm) 2, 4시간 조사구의 5처리를 난괴법 3반복으로 실험하였다. LEDs 보광은 일몰후 처리별로 조사하였으며 처리시기는 화아분화기와 착색기에 각각 1개월씩 보광하였다. 실험결과 적색광 LEDs 보광에 의해 대조구에 비해 적색 LED 처리구에서 엽중이 늘어났으나 초적색 LEDs 보광에서는 엽중이 감소하였으며 보광시간이 길어질수록 더욱 감소하였다. 2009년에는 무처리구인 대조구에 비해 LEDs 처리구에서 과중이 증가하였으며 특히 적색광 LEDs 처리구에서 188g 이하의 소과 발생도 없었고 300g 이상 과실도 많았다. 2010년에는 250g 이상 과실이 대조구에 비해 적색광 2, 4시간 보광에서 증가하였으나 초적색광 보광에서는 대조구에 비해 감소하였다. 과실의 경도는 대조구에 비해 초적색광 2, 4시간 보광에서 증가하였으며 당도에서는 큰 차이를 나타내지 않았다. 착색도에 있어서는 적색 LEDs 처리구가 대조구에 비해 Hunter a 값이 낮아지는 경향을 나타냈으나 초적색광에서는 높아지는 경향을 나타냈다. 이상의 결과를 통해 살펴보면, 적색광은 홍로 사과의 과중을 증가시켰으나 초적색광은 Hunter a 값을 높이는 결과를 나타냈다. 이에 앞으로 사과원에서의 LEDs의 효과적인 이용을 위해 적색광과 초적색광 단용처리가 아닌 혼합처리를 하여 각각의 광원의 효과가 상승적으로 작용하는지에 대한 추가적인 연구가 필요할 것으로 판단되었다.
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We demonstrate two kinds of 3D LEDs structure: warm white emission nano-pyramid LEDs and tip-free nanorod LEDs. The characteristics of 3D LEDs were discussed, which could be a future innovation for solid state lighting.
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Pyramid (geometry)
Wide-bandgap semiconductor
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High-power Light Emitting Diodes (LEDs) were introduced in the market in 1998 by Lumileds. High-power LEDs have unique properties, very different from conventional light sources, creating never before possible solutions available to lighting designers. In this paper we will give an update on these devices and discuss the main benefits of LEDs compared to more traditional light sources. We will show that the benefits of high-power LEDs also relate to the organization of light they emit. Comparisons of more and less organized light sources as well as applications for highpower LEDs will be discussed.
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GaN-based light-emitting diodes (LEDs) with graded-thickness quantum wells and barriers (GMQW-LEDs) are fabricated and researched in this letter. The light power and carrier distribution of GMQW-LEDs are compared with those of LEDs with original uniform MQW (OR-LEDs), graded-thickness quantum wells (GQW-LEDs), and graded-thickness quantum barriers (GQB-LEDs) through numerical simulation, respectively. The experimental results show that light power of GMQW-LEDs is enhanced significantly compared with that of OR-LEDs. The simulation results reveal that GMQW-LEDs show light output power enhancements of 25.7%, 14.3%, and 9.2% compared with OR-LEDs, GQW-LEDs, and GQB-LEDs at current density of 100 A/cm 2 , respectively. This is due to the superior hole distribution in quantum wells, which inhibits the electron leakage and enhances the radiative recombination.
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Wide-bandgap semiconductor
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Lattice constant
Iron nitride
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The purpose of this study was to determine optimum condition for the cultivation of Chlorella sp. FC-21, which is a freshwater microalgae, using light emitting diodes (LEDs). Specific growth rate and cell concentration were measured for the reactors at the illumination of different wavelengths of LEDs. Among various types of LEDs, red LEDs were the most effective light source, and also greatest increases of specific growth rate and cell concentrations were obtained when light intensity of red LEDs increased. From this study, we found that red LEDs were the most appropriate light source for the cultivation of Chlorella sp. FC-21.
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UV-A LEDs have seen efficiencies reach almost 70% and a substantial reduction in cost over the last few years. These trends have enabled UV-LED-based curing to become a mainstream application with most LEDs being driven at 1-2 A/mm2. At the same time novel applications, such as high-volume 3D Printing requiring higher power from UV LEDs have started to emerge. To address these applications, and to improve system speed in traditional applications, Luminus Devices has developed UV-A LEDs that can be operated at up to 4 A/mm2 which is the highest current density of any commercially available LED on the market. These next generation LEDs are very reliable and at 4 A/mm2 enable up to 74% higher power than LEDs driven at 2 A/mm2. This paper presents the performance characteristics of these nextgeneration LEDs, the novel and emerging applications they enable and provides a roadmap for future performance gains. UV-C LEDs are starting to become commercially viable but have low wall-plug efficiencies of 2%-4% and power levels reaching 100 mW. UV-C LEDs are not only replacing lamps but creating entirely new markets. The current status of UV-C LEDs is presented along with a discussion of the applications the LEDs will enable over the next 2-3 years.
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