LED Substrate Light Scattering Voids for Extraction Efficiency
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Solution Overview
Problem
Conventional GaN-based LEDs suffer from low light extraction efficiency due to total internal reflection and absorption by the substrate and metal contacts, which reduces the percentage of generated photons that escape the LED die.
Innovation Solution
Incorporating light scattering areas, such as voids or reflective particles, into the growth substrate or replacing the substrate with a new one containing light scattering features to redirect light away from absorbing areas and reduce guided light within the substrate, thereby enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a transparent substrate is used to allow light extraction, then light can exit the LED die, but total internal reflection and light guiding in the substrate reduce light extraction efficiency
Solution Approach 1:
The substrate is designed with an array of through-holes or voids that extend through its thickness. These porous features disrupt the continuous transparent medium, preventing light guiding and total internal reflection while still allowing light extraction. The voids scatter light rays that would otherwise be trapped, improving light extraction efficiency without compromising the substrate's transparency function.
2Loss of energy
If light scattering areas are added to the substrate, then light extraction efficiency increases, but the substrate structure becomes more complex
Solution Approach 1:
The substrate is segmented into multiple regions by creating an array of discrete through-holes or voids. Each void acts as an independent light scattering element, and the collective array provides comprehensive light extraction enhancement. This segmentation approach achieves the desired optical function while maintaining a relatively simple manufacturing process using standard photolithography and etching techniques.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The implementation of light scattering areas effectively increases light extraction efficiency by minimizing absorption and guiding, allowing more photons to escape the LED die, leading to improved brightness and color uniformity.
Implementation Method 1
the transparent growth substrate of an LED die is formed to have light scattering areas, such as voids formed using a laser or other method
Implementation Method 2
the substrate may be formed to include reflective particles, such as TiO2 particles or reflective metal flakes, in selected areas
Implementation Method 3
One contribution to light absorption is total internal reflection (TIR) by the substrate 18, shown by the light ray 24 being trapped inside the substrate 18, where the substrate 18 acts as a light guide
Data Source
AI summary
In one embodiment, the transparent growth substrate of an LED die is formed to have light scattering areas, such as voids formed by a laser. In another embodiment, the growth substrate is removed and replaced by another substrate that is formed with light scattering areas. In one embodiment, the light scattering areas are formed over the light absorbing areas of the LED die, to reduce the amount of incident light on those absorbing areas, and over the sides of the substrate to reduce light guiding. The replacement substrate may be formed to include reflective particles in selected areas. A 3D structure may be formed by stacking substrate layers containing the reflective areas. The substrate may be a transparent substrate or a phosphor tile that is affixed to the top of the LED.