We fabricated three types of high luminous efficacy white light emitting diodes (LEDs). The first was a white LED with a high luminous efficacy (ηL) of 249 lm W−1 and a high luminous flux (ϕv) of 14.4 lm at a forward-bias current of 20 mA. This ηL was approximately triple that of a tri-phosphor fluorescent lamp (90 lm W−1). The blue LED used as the excitation source in this white LED had a high output power (ϕe) of 47.1 mW and a high external quantum efficiency (ηex) of 84.3%. The second was a high-power white LED, fabricated from the above high-power blue LED, and had a high ϕe of 756 mW at 350 mA. ϕv and ηL of the high-power white LED were 203 lm and 183 lm W−1 at 350 mA, respectively. The third was a high-power white LED fabricated from four high-power blue LED dies. ϕv and ηL of the high-power white LED were 1913 lm and 135 lm W−1 at 1 A, respectively. The white LED had a higher flux than a 20 W-class fluorescent lamp and 1.5 times the luminous efficacy of a tri-phosphor fluorescent lamp (90 lm W−1).

We fabricated three types of high luminous efficiency white light emitting diodes (LEDs). The first is the white LED, which had a high luminous efficiency ( L ) of 161 lm/W with the high luminous flux ( v ) of 9.89 lm at a forward-bias current of 20 mA. The blue LED had a high output power ( e ) of 42.2 mW and a high external quantum efficiency ( ex ) of 75.5%. The second is the high luminous efficiency white LED with a low forward-bias voltage (V f ) of 2.80 V, which was almost equal to the theoretical limit. L and wall-plug efficiency (WPE) were 169 lm/W and 50.8%, respectively, at 20 mA. They were 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 e of 651 mW at 350 mA. v , L , and WPE of the high power white LED were 145 lm, 134 lm/W, and 39.6% at 350 mA, respectively.

We fabricated high-output-power 255 and 280 nm light-emitting diodes (LEDs) using direct bonding. The LED chips were bonded to sapphire lenses at room temperature using either atomic diffusion bonding or surface-activated bonding. The LEDs with lenses had a higher light extraction efficiency than conventionally structured LEDs. As a result, at a forward current of 350 mA, the output power of the 255 nm LED increased by a factor of 2.8, reaching 73.6 mW, while that of the 280 nm LED increased by a factor of 2.3, reaching 153 mW.

We reviewed the structural and optical properties of high output power 255 and 280 nm light-emitting diodes (LEDs) bonded with hemispherical lenses made of inorganic materials. [This is described as a full paper (and not a review). Is this your intended meaning?][This is my intended] The optimal LED structure with a lens to improve the output power for deep ultraviolet LEDs was designed using Monte Carlo simulation. The LED chips were bonded to sapphire lenses at room temperature using either atomic diffusion bonding or surface activated bonding. The bonding of the lenses to the LEDs is experimentally shown to improve the light extraction efficiency, and the light output power of the LEDs with lenses was significantly higher than that of conventional structure LEDs. The output power of a 255 nm LED with a lens was 2.8 times larger than that without a lens, with a maximum external quantum efficiency of 4.56%, and that of the 280 nm LED with a lens was larger by a factor of 2.3.