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Sided Patterned Sapphire Substrate to Improve The Performance of The Light Emitting Diode

 The modeled GaN based LED chips have an area of 350×350  μm² and a thickness of 85 μm. The thickness of the sapphire substrate in the multilayered structure is 80 μm. An n-GaN layer with a 4 μm thickness was placed on the sapphire substrate and a multiquantum well (MQW) with a 100 nm thickness was placed on top of it as the active layer. A 1-μm-thick p-GaN layer was then added. A 300-nm-thick transparent electrode indium tin oxide (ITO) layer was added to the top layer. Since the bottom of the LED element is the printed circuit board and thus does not pass any light, the bottom part of the LED was modeled to be reflective. Table 1 shows the optical properties of the LED components.

For the refractive index, the sapphire is set to 1.71, the air to 1, the p-GaN layer to 2.43, and the n-GaN layer to 2.61. In the case of the MQW, the refractive index of the multiple layers was set to 2.61. Epoxy with a refractive index of 1.41 was used for the LED chip encapsulant. When light is emitted from the LED element, the critical angle is around 23 deg, since the element and air have a refractive index. This means that only the light within the critical angle of 23 deg can be emitted outside. An accurate simulation epoxy was used for the LED element encapsulant. Another optical property that must be considered is the absorption. The absorption factor depends on the medium.


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