Global Sources
EE Times-India
Stay in touch with EE Times India
 
EE Times-India > Power/Alternative Energy
 
 
Power/Alternative Energy  

Researchers boost performance of LEDs

Posted: 14 Jan 2009     Print Version  Bookmark and Share

Keywords:LED  lighting  density currents  polarisation 

Rensselaer Polytechnic Institute researchers have developed and demonstrated a new type of LED with significantly improved lighting performance and energy efficiency.

The new polarisation-matched LED, developed with Samsung Electro-Mechanics, exhibits an 18 per cent increase in light output and a 22 per cent increase in wall-plug efficiency, which essentially measures the amount of electricity the LED converts into light.

The new device achieves a notable reduction in "efficiency droop," a well-known phenomenon that provokes LEDs to be most efficient when receiving low-density currents of electricity, but then to lose efficiency as higher density currents of electricity are fed into the device. The cause of this droop is not yet fully understood, but studies have shown that electron leakage is likely a large part of the problem.

"This droop is under the spotlight since today's high-brightness LEDs are operated at current densities far beyond where efficiency peaks," said 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.

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

Focusing on the active region of LEDs where the light is generated, Schubert's team discovered the region contained materials with mismatched polarisation. The polarisation mismatch likely causes electron leakage, and therefore a loss of efficiency, Schubert said.

Band diagram of conventional GaInN/GaN active region and new polarisation-matched GaInN/GaInN active region of a light-emitting diode.

The researchers discovered that the polarisation 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, and replaced it with Gallium Indium Nitride/ Gallium Indium Nitride (GaInN/GaInN). This substitution allows the layers of the active region to have a better matched polarisation, and in turn reduce both electron leakage and efficiency droop.

The benefits seen by testing the new GaInN/GaInN LED were consistent with theoretical simulations showing polarisation matching reducing electron leakage and efficiency droop.

1 • 2 Next Page Last Page



Comment on "Researchers boost performance of LED..."
Comments:  
*  You can enter [0] more charecters.
*Verify code:
 
 
Webinars

Seminars

Visit Asia Webinars to learn about the latest in technology and get practical design tips.

 

Go to top             Connect on Facebook      Follow us on Twitter      Follow us on Orkut

 
Back to Top