UC Santa Barbara Researchers Set New Records in Energy Efficient Light Emitting Diodes

This new class of gallium nitride-based LEDs is based on new nonpolar and semipolar orientations of GaN with record external quantum efficiencies, and they exhibit polarized light emission.

The new non-polar LEDs have an external quantum efficiency of 41% and radiant powers as high as 25 mW for standard sizes (300 µm x 300 µm) and operating current (20 mA). The semipolar LEDs exhibited external quantum efficiency of 30% and radiant powers as high as 18 mW, also for standard chip sizes and operating current (20 mA). The polarized light emission will enable a new class of light sources and will be useful in applications such as LCD backlighting. Dr. DenBaars stated that these recent achievements in high power nonpolar LEDs represent almost an order of magnitude improvement in efficiency and brightness over previous reports.

The groups led by Shuji Nakamura, Steve DenBaars and James Speck -- all professors of materials -- have also achieved c-plane LEDs with external quantum efficiencies of 66%. These LEDs have been used to make white LED lamps which boast a luminous efficacy of 116 lm/W  more efficient than both incandescent bulbs and fluorescence lamps. Dr. Nakamura commented on the improved efficiency, saying that these results further confirm that white LEDs could save billions of dollars in energy costs and help reduce greenhouse gases associated with electricity production.

The commercial applications of nonpolar LEDs include LCD backlighting, projections televisions, medical imaging and general illumination. Dr. Speck noted that these results "...validate our premise that nonpolar GaN would enable commercially viable high performance GaN light emitting devices."

Research funding was provided by the Solid State Lighting & Display Center and by JST ERATO. UCSBs Solid State Lighting & Display Center, www. ssldc.ucsb.edu, is focused on advancing new semiconductor-based energy efficient lighting and display technologies through partnerships with key industry leaders.

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