Position of Ag reflection layer and its effect on GaN LED light extraction efficiency

We uses Finite Difference Time Domain (FDTD) based simulations directly compare six state of art GaN LED structures. The six structures include three conventional LEDs, and three LEDs with a patterned sapphire substrate and SiO2 nanorod array. Since Ag reflection layers have been used recently in Gallium Nitride (GaN) LEDs to improve light extraction efficiency. A reflection layer is placed either between the U-GaN and sapphire layers or at the bottom of the sapphire substrate in our simulation. We present the effect of Ag reflection layer position on output power for each structure. With the reflection layer located at the bottom of the sapphire substrate, we show that changing sapphire substrate height strongly affects light extraction efficiency. The conventional LED with an appropriate sapphire height design and a bottom Ag reflector can be the most efficient device.