RPI researchers use streamlined polarization to boost performance of LEDs

Researchers at Rensselaer Polytechnic Institute (RPI) have developed and demonstrated a new type of LED with significantly improved lighting performance and energy efficiency. The researchers worked in collaboration with Samsung Electro-Mechanics to develop the new polarization-matched LED that they say exhibits an 18 percent increase in light output and a 22 percent increase in wall-plug efficiency, which essentially measures the amount of electricity the LED converts into light.

   Band diagrams: conventional (above) and new method (below)

The researchers note that the new device achieves a reduction in “efficiency droop,” a phenomenon that gives LEDs the most efficiency when receiving low-density currents of electricity, but to lose efficiency as higher density currents of electricity are fed into the device.

This droop is under the spotlight since today’s high-brightness LEDs are operated at current densities far beyond where efficiency peaks, according to project leader E. Fred Schubert, Wellfleet Senior Constellation Professor of Future Chips at Rensselaer, and head of the university’s National Science Foundation-funded Smart Lighting Engineering Research Center.

Schubert said this challenge has been a stumbling block, because reducing the current densities to values where LEDs are more efficient is unacceptable. Their new LED, however, which has a radically re-designed active region, namely a polarization-matched active region, tackles this issue and brings LEDs closer to being able to operate efficiently at high current densities.

Focusing on the active region of LEDs where the light is generated, Schubert’s team discovered the region contained materials with mismatched polarization. They discovered that the mismatch can be strongly reduced by introducing a new quantum-barrier design. They replaced the conventional gallium indium nitride/gallium nitride (GaInN/GaN) layer of the LED active region with GaInN/GaInN. This substitution allows the layers of the active region to have a better matched polarization, and in turn reduces both electron leakage and efficiency droop.

In October, Rensselaer announced its new Smart Lighting Research Center, in partnership with Boston University and the University of New Mexico, and funded by an $18.5 million, five-year award from the NSF Generation Three Engineering Research Center Program. The three primary research thrusts of the center are developing novel materials, device technology, and systems applications to further the understanding and proliferation of smart lighting technologies.

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