LED Composite High Reflectivity Layer for Optical Loss Reduction
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) face limitations in light extraction efficiency due to total internal reflection (TIR) caused by the large difference in refractive index between the semiconductor material and surrounding ambient, leading to optical losses and reduced brightness, despite the use of reflective surfaces which often have less than 100% reflectivity.
Innovation Solution
A composite high reflectivity layer is introduced, comprising a thick dielectric layer with alternating thinner layers of different refractive materials, which provides improved reflectivity across various viewing angles, minimizing optical losses and enhancing light emission efficiency by reflecting light back towards the primary emitting surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single metal reflective layer is used in LEDs, then the device complexity is low, but the reflectivity is insufficient (less than 100%) causing optical losses
Solution Approach 1:
The patent applies composite materials by combining multiple dielectric layers with different refractive indices (high index layer and low index layer) to form a distributed Bragg reflector structure. This composite layering achieves near 100% reflectivity through constructive interference of reflected light waves, resolving the contradiction between simple structure and high reflectivity by using a systematically designed multi-layer composite rather than a single material.
Solution Approach 2:
The patent utilizes parameter changes by precisely controlling the thickness of each dielectric layer to be one-quarter of the wavelength of light in that medium. This specific thickness parameter, combined with alternating high and low refractive index materials, creates the conditions for maximum reflectivity through optical interference, transforming the reflectivity parameter from insufficient to near 100%.
2Productivity
If surface texturing is applied to increase light extraction, then light extraction efficiency improves, but the device complexity increases
Solution Approach 1:
The patent addresses light extraction by introducing a vertical dimension solution through the distributed Bragg reflector structure beneath the active region. Instead of modifying the surface topology (horizontal dimension), the invention uses vertical layering with alternating refractive indices to reflect light back through the active region, achieving enhanced extraction without surface complexity.
3Illumination intensity
If multiple reflections occur in conventional reflectors, then light is redirected towards emission, but cumulative optical losses increase
Solution Approach 1:
The patent converts the harmful effect of multiple reflections (which cause cumulative losses in conventional metal reflectors) into a benefit by using a distributed Bragg reflector. The multi-layer dielectric structure is designed so that each reflection at the interfaces between high and low index layers is constructive rather than lossy, achieving high reflectivity with minimal absorption since dielectric materials have negligible optical loss compared to metals.
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 composite layer achieves near 100% reflectivity at certain angles and an average reflectivity of approximately 98.79% across 0-90 degrees, significantly improving the overall brightness of LEDs by reducing cumulative losses from multiple reflections.
Implementation Method 1
For conventional LEDs with a single out-coupling surface, the external quantum efficiency can be limited by total internal reflection (TIR) of light from the LED's emission region
Implementation Method 2
TIR can be caused by the large difference in the refractive index between the LED's semiconductor and surrounding ambient
Implementation Method 3
A composite high reflectivity layer is introduced, comprising a thick dielectric layer with alternating thinner layers of different refractive materials, which provides improved reflectivity across various viewing angles
Data Source
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AI summary
A high efficiency light emitting diode with a composite high reflectivity layer (62) integral to said LED to improve emission efficiency. One embodiment of a light emitting diode (LED) chip comprises ah LED and a composite high reflectivity layer (62), integral to the LED to reflect light emitted from the active region (54). The composite layer comprises a first layer (66), and alternating plurality of second (68) and third (70) layers on the first layer (66), and a reflective (71, 126) layer on the topmost of said plurality of second and third layers. The second and third layers have a different index of refraction, and the first layer is at least three times thicker than the thickest of the second and third layers. For composite layers internal to the LED chip, conductive vias (128) can be included through the composite layer to allow an electrical signal to pass through the composite layer to the LED.