Red-enhanced white light-emitting diodes using external AlGaInP epilayers with various aperture ratios

A novel hybrid white light-emitting diode (LED) is proposed to enhance the red color and stability of the chromaticity under various operating currents using an AlGaInP photon-recycling (PR) epilayer. A blue/yellow white InGaN LED sample is covered with an external patterned AlGaInP epilayer. Under an optimum aperture ratio of 30%, the luminous efficiency of the PR-LED lamp can achieve a color coordinate of (x=0.340, y=0.295). When the injection current increases from 50 to 350 mA, the color temperature decreases from 4030 to 3700 K and the color rendering index increases from 81 to 86. These could be due to the fact that the AlGaInP epilayer was not attached onto the LED chip, alleviating the thermal effect on the color coordinate. The present white PR-LED samples have high potential for portable liquid-crystal-display backlight applications.