Prediction of light extraction efficiency of LEDs by ray trace simulation

The advantage of enhancing the light extraction of LED dies is twofold: it increases the overall efficiency of the device, reducing internal absorption and subsequently the temperature of the device. We have developed the solid model of a commercially available blue LED in a ray tracing simulation software according to the physical structure of the GaN die grown on SiC substrate. Optical parameters of the various device layers were adjusted within a plausible range to achieve the best match between the measured and the simulated spatial luminous intensity profile. Two approaches for improving the light extraction efficiency were examined using the model: change of refractive index of the encapsulating medium and chip shaping. Simulation results were verified by a series of luminous intensity and total flux measurements in a mini-goniophotometer. We found that the physical experiment confirmed the predicted results.