Saw-Toothed LED Multilayer for Thermal Stress and Light Extraction
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Solution Overview
Problem
Conventional LEDs, particularly those using sapphire substrates, suffer from low light extraction efficiency due to light scattering and absorption, and existing solutions like distributed Bragg reflectors face issues with thermal stress and peeling, limiting their effectiveness.
Innovation Solution
The implementation of a saw-toothed multilayer with a photonic crystal structure acts as an omnidirectional reflector, enhancing light extraction by reflecting light emitted at any angle and focusing it forward, while also mitigating thermal stress through appropriate material selection and layer design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a planar multi-layer dielectric (DBR mirror) is used to reflect light, then reflectivity is improved, but thermal stress and peeling occur during high temperature epitaxial process
Solution Approach 1:
The patent applies asymmetry by transforming the planar DBR mirror structure into a three-dimensional saw-toothed multilayer structure. This asymmetric geometry provides mechanical compliance during thermal expansion while maintaining optical reflectivity function, resolving the contradiction between high reflectivity and structural integrity under thermal stress
Solution Approach 2:
The invention transitions from a two-dimensional planar DBR mirror to a three-dimensional saw-toothed multilayer structure with vertical and lateral dimensions. This dimensional change allows the structure to accommodate thermal stress through out-of-plane deformation while preserving the in-plane optical reflection functionality
2Illumination intensity
If a one-dimensional periodic light grid structure is used to refract light, then forward light emission is improved, but vertical incident light is not refracted effectively
Solution Approach 1:
The patent enhances the one-dimensional light grid structure by adding vertical saw-toothed multilayer architecture, creating a multi-dimensional photonic crystal structure. This enables the structure to interact with light across a broader range of incidence angles while maintaining forward emission enhancement
Solution Approach 2:
The combined saw-toothed multilayer and light grid structure serves multiple functions simultaneously: it acts as an omnidirectional reflector for vertical incident light, maintains forward light emission enhancement, and provides mechanical stress relief, achieving universal functionality across different light propagation scenarios
3Ease of manufacture
If sapphire substrate is used in conventional LED, then fabrication is simplified, but light scattering and absorption reduce extraction efficiency
Solution Approach 1:
The patent maintains the sapphire substrate for ease of fabrication but introduces localized photonic crystal structures (saw-toothed multilayer with light grid) at specific regions to enhance light extraction. This local quality modification improves light extraction efficiency without compromising the overall fabrication simplicity of using sapphire substrate
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
This approach significantly increases the luminescent efficiency of LEDs by ensuring that nearly all emitted light is reused as forward-emitting light, with reflectivity exceeding 99% within the desired wavelength range, and maintains structural integrity even under high temperature epitaxial processes.
Implementation Method 1
a saw-toothed multilayer with a photonic crystal structure acts as an omnidirectional reflector, enhancing light extraction by reflecting light emitted at any angle and focusing it forward
Implementation Method 2
reflecting light emitted at any angle and focusing it forward
Implementation Method 3
a one-dimensional periodic light grid structure may allow a portion of back light to be refracted so as to emit forward
Data Source
AI summary
A light emitting diode (LED) is provided. The LED at least includes a substrate, a saw-toothed multilayer, a first type semiconductor layer, an active emitting layer and a second type semiconductor layer. In the LED, the saw-tooth multilayer is formed opposite the active emitting layer below the first type semiconductor layer by an auto-cloning photonic crystal process. Due to the presence of the saw-tooth multilayer on the substrate of the LED, the scattered light form a back of the active emitting layer can be reused by reflecting and recycling through the saw-tooth multilayer. Thus, all light is focused to radiate forward so as to improve the light extraction efficiency of the LED. Moreover, the saw-tooth multilayer does not peel off or be cracked after any high temperature process because the saw-tooth multilayer has the performance of releasing thermal stress and reducing elastic deformation between it and the substrate.