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

Laser Focus World, 12/16/2016

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).