Optical EngineeringStudy of photon extraction efficiency in InGaN light-emitting diodes depending on chip structures and chip-mount schemes
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The performance of InGaN LEDs in terms of photon extraction efficiency is analyzed by the Monte Carlo photon simulation method. Simulation results show that the sidewall slanting scheme, which works well for the AlInGaP or InGaN/SiC system, plays a very minimal role in InGaN/sapphire systems. In contrast to InGaN/SiC systems, a lower refractive index sapphire substrate restricts the generated photons to enter the substrate, minimizing the chances for the photons to be deflected by the slanted sidewalls of the epitaxial semiconductor layers that are usually very thin. The limited photon transmission to the sapphire substrate also degrades the photon extraction efficiency, especially in the epitaxial side down mount. One approach to exploit the photon extraction potential of the epitaxial side down mount may be to texture the substrate-epitaxy interface, by possibly growing the epitaxial layers on a sapphire substrate that is either appropriately surface textured or patterned and etched. In this case, randomized photon deflection off the textured interface directly increases the number of photons entering the sapphire substrate, from which they easily couple out of the chip, thereby improving the photon extraction efficiency drastically.