The significant drop in efficacy as input power increases in green LEDs (green gap phenomenon) has frequently been the cause of efficiency problems and high costs in customer applications. For its indium gallium nitride (InGaN)-based green LEDs, Osram Opto Semiconductors reports that the company has now successfully reduced the typical forward voltages dramatically by about 600 mV. With a simultaneous increase in optical output, the efficiency of Osram Opto’s latest InGaN green LED demonstrated an improvement of up to 40 percent compared to the company’s previous products across the entire UX:3 portfolio.
According to the company, its developers have managed to reduce the typical forward voltages of green direct emitting InGaN LEDs by 600 mV to 2.6 V at power densities of 45 A/cm2. Notably, the benefits of such efficiency enhancements are substantial, particularly for applications that use red, blue and green LEDs in combination. Now, because red, blue, and green LEDs have a voltage of less than 3 V the drivers, which were previously intended for higher maximum voltages, can now be made smaller. This size reduction results in a decrease in both dissipative power loss and costs.
Green LEDs Achieve 175 LPW at 350mA
Osram Opto Semiconductors cited optimized material quality in the epitaxial layers and enhanced charge carrier transport as the critical factors resulting in the improved efficiency of the green LEDs. Green 1-mm2 UX:3 LED chips with wavelengths about 530 nm using the new technology at an input voltage of 350 mA, obtain efficiencies of 175 lumens per Watt (LPW) and higher. When they boosted the power input to 1 A, the absolute light output of the green LEDs can now exceed 300 lm.
“Until recently, these efficiency values seemed unattainable for green direct emitting InGaN LEDs. We are now moving into areas that up to now have been achievable only with phosphor conversion emitters but with significantly reduced spectral quality. Thanks to the success of our development team we have been able to drastically reduce the green gap phenomenon for our customers,” said project manager Adam Bauer from Osram Opto Semiconductors.
The team is currently working on improvements that offer potential for the company’s green LED products as a result of the recent findings.