Nichia's white-emitting LED chips hit 138 lm/W
Japanese LED chip manufacturer Nichia has produced a small white-emitting LED chip that has an efficacy of 138 lm/W at 20 mA, and a larger device that delivers 92 lm/W at 350 mA.
The small chip, which measures 240 µm x 420 µm, has a color temperature of 5450K, a wall plug efficiency of 41.7% , and a forward voltage of 3.11 V at 20 mA.
The 1 mm x1 mm chip has a slightly lower color temperature and efficacy, but can deliver 106 lumens at 350 mA and 402 lumens at 2A, which is equivalent to the total flux of a 30W incandescent lamp.
Both of the MOCVD-grown devices produce white light by exciting a yellow YAG phosphor with 450 nm emission from an InGaN/GaN LED. The high efficacy of the chips results from improvements in external quantum efficiency, according to Nichia's researchers.
The LEDs do not use a conventional translucent Ni/Al p-contact that has a transmittance of only 40 %, but instead employ an indium tin oxide electrode with a transmittance of 95 %.
Extraction efficiency is also boosted by growth on a sapphire substrate patterned with convex hexagons, which scatter more of the light emitted from the active layer.
Nichia's results compare favorably with those of Cree, which reported a white LED chip delivering 131 lm/W at 20 mA this summer (see related story). Nichia's results were obtained using pulsed operation (200Hz repition rate, and a duty cycle of 1 %). Cree provided no details of its mode of operation.
Nichia's results have been presented at the recent International Workshop on Nitride Semiconductors that was held in Kyoto, Japan, and are described in more detail in the Japanese Journal of Applied Physics 45 L1084-L1086.
