Osram Opto Semiconductors GmbH of Regensburg, Germany has succeeded in reducing the typical forward voltage by about 600mV to 2.6V (at a power density of 45A/cm2) in its indium gallium nitride (InGaN)-based green direct-emitting LEDs. With a simultaneous increase in optical output power, efficiency can be instantly improved by up to 40% compared to predecessor products across the firm’s entire UX:3 portfolio. The significant drop in light output (the ‘green gap’ phenomenon) exhibited by green LEDs has often been the cause of efficiency problems and high costs in customer applications.
The benefits can be considerable, particularly for applications in which red, blue and green LEDs used in combination. Because all three colors now have a voltage of less than 3V, the size of the drivers (previously designed for higher maximum voltages) can now be smaller. This in turn reduces both dissipative power loss and costs. The crucial factors in increasing efficiency were improved charge carrier transport and optimized material quality in the epitaxial layers.
At 350mA, 1mm2 UX:3 chips achieve efficiencies of 175lm/W and higher at wavelengths around 530nm with the new technology. Absolute light output in excess of 300lm at a pumping current of 1A opens up new applications, says Osram Opto.
“Until recently, these efficiency values seemed unattainable for green direct-emitting InGaN LEDs,” says project manager Adam Bauer. “We are now moving into areas that up to now have been achievable only with phosphor-conversion emitters but with significantly reduced spectral quality,” he adds. “Thanks to the success of our development team we have been able to drastically reduce the green gap phenomenon.”
The team is now working on further improvements that offer potential that has become evident as a result of the recent findings.
