Chien-Yuan Wang

Recent developments in high brightness LEDs

The internal quantum efficiency (IQE) of commercial ultra high brightness AlGaInP red LED has already reached 90% or higher but the light extraction efficiency was only about 30% to 50%. Through the improvement of surface texturing structure by nano-imprint technology and current spreading by using narrow width ohmic contact metal line, the light extraction efficiency of AlGaInP red LED was significantly improved up to 60%. In AlGaInN LED, the thermal resistance of the LED chip can be reduced by thinning down or totally removing the sapphire substrate and then replacing it by high thermal conductivity materials. Therefore, the performances of high power AlGaInN LED chips were improved in high current density operation condition.