LED Reflective Layer Structure for Higher Light Extraction
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Solution Overview
Problem
Conventional light-emitting diodes (LEDs) face challenges in maximizing light emission efficiency due to internal reflection, which limits the extraction of light emitted by the active region and results in optical losses.
Innovation Solution
The implementation of a light-emitting diode (LED) chip with a reflective layer structure that includes a plurality of dielectric layers with varying thicknesses, forming an aperiodic Bragg reflector, to enhance light reflection and reduce internal losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single-layer reflective surface is used in conventional LEDs, then the device structure is simple, but the reflectivity is insufficient (less than 95%) causing optical losses
Solution Approach 1:
The reflective layer is segmented into multiple sub-layers (first reflective sub-layer, second reflective sub-layer, third reflective sub-layer) with different materials and optical properties. Each sub-layer contributes to reflecting light at different angles and wavelengths, achieving high reflectivity (greater than 95%) across a broad spectral range while managing the complexity through systematic segmentation.
Solution Approach 2:
The patent employs composite reflective layer structure combining different materials (silver, aluminum, dielectric materials) in a multi-layer configuration. This composite approach leverages the complementary strengths of each material to achieve broadband high reflectivity that single materials cannot provide alone, resolving the contradiction between simplicity and performance.
2Loss of energy
If mechanical methods are used to texture the LED surface to increase light extraction, then light extraction efficiency improves, but stress or breakage of LED material occurs
Solution Approach 1:
The patent replaces mechanical texturing methods with a chemically-based solution using wet-etched sacrificial layers. This substitution eliminates mechanical stress and breakage risks while achieving the desired light extraction enhancement through controlled chemical etching processes that create extraction-enhancing features without compromising material strength.
Solution Approach 2:
The patent introduces sacrificial layers (amorphous silicon, silicon nitride) as intermediary elements that facilitate light extraction enhancement. These sacrificial layers are deposited and then selectively removed to create extraction-enhancing features, serving as a mediator between the deposition process and the final light extraction structure, avoiding direct mechanical intervention on the LED chip.
3Loss of energy
If chemical etching methods are used to enhance light extraction, then light extraction efficiency improves, but misalignment or microfeature damage occurs during subsequent fabrication
Solution Approach 1:
The patent performs the light extraction enhancement by removing sacrificial layers early in the fabrication sequence, before subsequent micropattern formation and device assembly steps. This preliminary action ensures that extraction-enhancing features are established before any alignment-critical or microfeature-sensitive operations, preventing misalignment and damage to fine structures during later processing.
Solution Approach 2:
Instead of etching the LED chip directly (which risks damage), the patent inverts the approach by depositing sacrificial layers first and then selectively removing them. This inverted sequence allows extraction-enhancing features to be created through material removal of the sacrificial layer rather than direct etching of the LED chip, thereby avoiding microfeature damage while maintaining manufacturing precision.
4Ease of operation
If metal reflectors are used in LED packages, then light direction control improves, but optical losses occur due to less than 100% reflectivity
Solution Approach 1:
The patent changes the optical parameters of the reflective surface by using multiple layers with different refractive indices and optical properties. The multi-layer structure (including dielectric layers and metal layers) creates constructive interference and enhanced reflection across broad angles and wavelengths, achieving greater than 95% reflectivity while maintaining light direction control, thereby reducing optical losses compared to single-layer metal reflectors.
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 configuration significantly improves the reflectivity of the LED chip, leading to increased light extraction efficiency and reduced optical losses, thereby enhancing the overall emission efficiency of the LED.
Implementation Method 1
a reflective layer structure that includes a plurality of dielectric layers with varying thicknesses, forming an aperiodic Bragg reflector
Implementation Method 2
photons reaching the surface (interface) between an LED surface and the surrounding environment are either refracted or internally reflected
Implementation Method 3
According to the well-understood implications of Snell's law, photons reaching the surface (interface) between an LED surface and the surrounding environment are either refracted or internally reflected
Data Source
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Figure 3~4
Figure 5A~5B
AI summary
A light-emitting diode (LED) chip with reflective layers having high reflectivity is disclosed. The LED chip may include an active LED structure including an active layer between an n-type layer and a p-type layer. A first reflective layer is adjacent the active LED structure and comprises a plurality of dielectric layers with varying optical thicknesses. The plurality of dielectric layers may include a plurality of first dielectric layers and a plurality of second dielectric layers of varying thicknesses and compositions. The LED chip may further include a second reflective layer that includes an electrically conductive path through the first reflective layer. An adhesion layer may be provided between the first reflective layer and the second reflective layer. The adhesion layer may comprise a metal oxide that promotes improved adhesion with reduced optical losses.