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Views: 0 Author: Anny Publish Time: 2021-05-26 Origin: https://www.suntechleds.com/
Driven by the COVID-19 epidemic, UVC LED disinfection products have attracted widespread attention, and UVC LED, a product that is still in the rapid development stage, has been pushed to the forefront.
Because UVC LED technology has yet to be perfected, there are no mature industry standards or national standards. And there is no recognized test standard for UVC LED chip radiant flux and radiant intensity measurement, so naturally, there is no UVC LED testing equipment that meets the standard.
When you search for a flexible UVC LED strip, rigid UVC LED board or UVC LED chip, there will be found various products with so different prices. Some prices of some products are indeed very attractive, in the long run, the most important thing to consider is the quality and performance of the products. The chip in the LED has the greatest impact on the performance of the LED lights. So this article will introduce in detail which parameters will affect the performance of the LED chip and how to test the LED chip.
The main preparation process of UVC-LED chips includes epitaxially growing buffer layer, n-type AlGaN, multiple quantum well light-emitting layer and p-type AlGaN on SiC or GaN) substrates, and then fabricating n-type ohmic contact layer and p-type ohmic contact layer respectively. Contact layer and electrode. The measurement and analysis of the macro-photoelectric characteristics can reflect the problems of the epitaxy and chip design and manufacturing process.
The ohmic contact layer of the UVC-LED chip has a great influence on turn-on voltage, voltage drop and I-V characteristics. At this stage, the quality of the p-type ohmic contact layer is particularly critical. A good-quality ohmic contact layer can reduce the turn-on voltage and series resistance of the chip, and improve the electro-optical conversion rate of the chip.
Chips with poor ohmic contact technology have very different forward voltage drops at different currents. Even if a chip with voltage bins is used, when multiple chips are used in parallel, it is easy to cause different current operating point selections, resulting in large differences in chip voltages, causing current "grabbing" effects, and affecting the reliability of the final product. Therefore, the discreteness of the I-V characteristic curve is first used as the standard for evaluating the quality of the chip. From the physical mechanism, this parameter mainly reflects the rationality and stability of the chip's ohmic contact process.
The epitaxial layer and the structure of the chip are the main factors affecting the electro-optical conversion efficiency of the LED. In addition, the growth quality of the epitaxial layer also has an important influence on the electro-optical conversion efficiency. The active layer of UVC LED is made of AlGaN material with high aluminum composition. The active layer of UVC-LED is made of AlGaN material with high aluminum composition. The defects of the active layer will increase the non-radiative recombination ratio and reduce the radiation recombination effectiveness. The direct reflection of various defect densities in the macro-photoelectric characteristics is the electro-optical conversion efficiency. Chips with high defect densities have low radiation efficiency and low radiation flux under the same current and voltage. Therefore, under the typical working current, the radiant flux and radiant efficiency are used as the second index to evaluate the quality of the UVC-LED chip.
If there are any defects in the epitaxial material or there are problems with the ohmic contact process, the heat caused by the large current will cause the electro-optical conversion efficiency of the chip to decrease, until the radiant flux saturation effect occurs. That is, the radiant flux or luminous flux of the LED no longer increases as the current increases, and even decreases as the current increases.
The I-V characteristic measurement of the chip is relatively simple. It can be measured directly with a tester, or a simple test system can be built with a constant current source and a voltmeter. For LED packaging manufacturers, you can directly use the current and voltage test system of the LED photoelectric characteristic comprehensive tester, use a pulsed power supply, measure the corresponding voltage by changing the current, and then draw the I-V characteristic curve. The system is composed of EVERFINE U-20 deep ultraviolet irradiance meter, LED light intensity distribution tester, and external drive power supply.
The LED light intensity distribution tester is equipped with a device for adjusting the angle and distance, which is convenient for measuring the radiation intensity at different angles and different distances. The test system is powered by a DC stabilized power supply. Through the output adjustment of the power supply, the current input to the LED can be precisely controlled.
During the measurement, the UVC-LED is fixed on the LED light intensity distribution tester, and the deep ultraviolet irradiance meter probe is placed in the center of the measuring device at a vertical distance of 3 cm. In the absence of a unified test standard, since the relative intensity is measured, this distance can be selected according to the sensitivity of the illuminance meter and the radiation intensity of the UVC LED. Rotate the angle dial on the LED light intensity distribution tester to measure the radiation intensity at different angles.
By comparing the radiation intensity values at each angle, the radiation flux of different devices can be estimated. Finally, the UVC LED was fixed at 0°, the driving current was changed, and the radiation intensity of LEDs packaged by different manufacturers was measured with the flow curve. Because under different currents, the radiation intensity at any angle is proportional to the radiation flux of the device, and the relationship between the radiation flux and the current change is consistent with the changing trend of the radiation intensity.
CREE, OSRAM, NICHIA, Toyoda Gosei, Agilent, TOSHIBA, Lumileds, SSC, Semileds, SDK.
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