Flip-chip GaN-based LED has 73% wall-plug efficiency

Dec. 16, 2016
A group is incorporating high-quality, low-voltage-drop GaN tunnel junctions into GaN-based LEDs to prevent current-spreading without adding to optical absorption.
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Content Dam Lfw Print Articles 2016 12 1612lfw Nb F3 Alt
Content Dam Lfw Print Articles 2016 12 1612lfw Nb F3 Alt
Content Dam Lfw Print Articles 2016 12 1612lfw Nb F3 Alt
Content Dam Lfw Print Articles 2016 12 1612lfw Nb F3 Alt

Years of research have gone into enabling blue-emitting gallium nitride (GaN)-based LEDs, which are the basis for the white-light LEDs used widely for lighting, to produce more lumens per watt and, similarly, have a higher wall-plug efficiency (optical output in watts per electrical input in watts). Because p-GaN, a material used to make efficient GaN-based LEDs, has poor electrical conductivity and results in current-spreading, transparent conducting-oxide LEDs and flip-chip LEDs with silver mirrors have been developed as added conductors. However, the silver mirror or conducting oxide absorbs light, reducing overall efficiency.

A group at the University of California, Santa Barbara that includes Shuji Nakamura, one of the inventors of the GaN-based LED, is incorporating high-quality, low-voltage-drop GaN tunnel junctions into GaN-based LEDs, rather than conducting mirrors or oxides, to prevent current-spreading without adding to optical absorption. The researchers have created non-flip-chip and flip-chip versions, with the latter incorporating a high-light-extraction multilayer dielectric mirror that increased the reflectivity of the wire-bond pads to greater than 98% at the LED's 450 nm operating wavelength. The resulting external quantum efficiency (EQE) and wall-plug efficiency (WPE) of the non-flip-chip device were 78% and 72%, respectively, and for the flip-chip LED were 76% and 73%, respectively. Patents are pending on both the tunnel-junction and light-extraction technologies developed by the researchers. Reference: B. P. Yonkee et al., Appl. Phys. Lett., 109, 191104 (2016).

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

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