Successful fabrication of white light emitting diodes by using extremely high external quantum efficiency blue chips

Abstract

AbstractWe fabricated three types of high luminous efficiency white light emitting diodes (LEDs). The first is the white LED, which had a high luminous efficiency (ηL) of 161 lm/W with the high luminous flux (ϕv) of 9.89 lm at a forwardbias current of 20 mA. The blue LED had a high power (ϕe) of 42.2 mW and high external quantum efficiency (ηex) of 75.5%. The second is the high luminous efficiency white LED with a low voltage (Vf) of 2.80 V, which was almost equal to the theoretical limit. ηL and wall‐plug efficiency (WPE) is 169 lm/W and 50.8%, respectively, at 20 mA. They are approximately twice higher than those of a tri‐phosphor fluorescent lamp (90 lm/W and 25%). The third is the high power white LED fabricated from the high power blue LED with high ϕe of 651 mW at 350 mA. ϕv, ηL and WPE of the high power white LED are 145 lm, 134 lm/W and 39.6% at 350 mA, respectively. Moreover, at 1 A, ϕv and ηL were 361 lm and 97 lm/W, respectively. Thus ϕv is equivalent to that of a 30 W‐class incandescent lamp. And, ηL is slightly higher than that of a tri‐phosphor fluorescent lamp. Moreover, we fabricated the high power near ultra‐violet, bluish‐green and green LEDs, whose ϕe at 350 mA were 675 mA, 325 mW, and 236 mW, respectively. ϕv of the green LED was 128 lm at 350 mA. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)