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Improved epitaxial processes reduce droop
Research success at Osram Opto Semiconductors. The high-tech company has considerably improved the luminous efficacy of its high-power LEDs by reducing the unwanted droop effect at high currents. This development was made possible by optimized epitaxial processes. At a current density of 3 A/mm² the quantum efficiency of the LEDs is now a full 7.5 percent above the previous level.
The unwanted drop in efficiency as the current density increases, commonly referred to as “droop”, limits the maximum luminous efficacy of indium gallium nitride based light emitting diodes (LEDs) and is therefore the subject of intense research and development activities worldwide. Engineers at Osram Opto Semiconductors have now been able to reduce this effect considerably and therefore achieve a significant increase in the efficiency of the LEDs. Under laboratory conditions and at a current density of 3 A/mm² a typical luminous flux of 740 lm was verified in a QFN LED package (Quad Flat No Lead) – an improvement of around 7.5 percent compared with previous typical values (6200 K, Cx 0.319, Cy 0.323, single-chip version LDxyz). At low current densities of 0.35 A/mm² the benefit of the optimized LEDs is still around 4 percent. “We have been able to reduce the droop effect considerably by extensively revising and improving the epitaxy”, said Dr. Alexander Frey, Project Manager at the Regensburg high-tech company.
The new processes are being used in all LEDs from Osram Opto Semiconductors based on UX:3 chip technology and will also have a positive impact on other high-power products. The results will now be integrated step by step in the existing product portfolio.
OSRAM, based in Munich, is a globally leading lighting manufacturer with a history dating back more than 100 years. The portfolio ranges from high-tech applications based on semiconductor technology, such as infrared or laser lighting, to smart and connected lighting solutions in buildings and cities. OSRAM had around 33,000 employees worldwide at the end of fiscal 2015 (September 30) and generated revenue of almost €5.6 billion in that fiscal year. The company is listed on the stock exchanges in Frankfurt and Munich (ISIN: DE000LED4000; WKN: LED 400; trading symbol: OSR). Additional information can be found at www.osram.com.