Patterned LED Substrate Surface for Light Extraction
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Solution Overview
Problem
Existing light-emitting diode (LED) technologies face challenges in enhancing luminance due to issues with light extraction efficiency and heat dissipation, particularly because surface roughening methods often result in poor epitaxial quality and difficulty in controlling pattern dimensions, leading to inefficiencies in both light extraction and heat dissipation.
Innovation Solution
A light-emitting device with a substrate featuring a patterned surface where the patterned units have non-polygon shapes in top view and inclined surfaces in cross-section, reducing the aspect ratio of the patterns to facilitate better epitaxial growth and improve light extraction efficiency, while minimizing parallel surfaces that cause total internal reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If surface roughening is performed by mechanical polishing to form randomly distributed rough patterns, then light extraction efficiency is improved, but manufacturing precision deteriorates due to difficulty in controlling pattern dimensions
Solution Approach 1:
The patent divides the substrate surface into a regular array of discrete patterned regions rather than using random roughening. Each pattern unit has controlled dimensions and spacing, achieving systematic light extraction enhancement while maintaining manufacturing precision through photolithographic patterning processes.
Solution Approach 2:
The patent employs curved or rounded pattern profiles (such as hemispherical or dome-shaped structures) instead of sharp angular features. This curvature design optimizes light extraction by reducing total internal reflection while maintaining structural integrity and facilitating precise fabrication through standard semiconductor processing techniques.
2Loss of energy
If pattern depth is increased to compensate for light loss in parallel regions, then light extraction efficiency is improved, but device complexity increases due to high aspect ratio patterns
Solution Approach 1:
The patent transitions from deep vertical patterns to shallower patterns with optimized lateral dimensions. By adjusting the pattern pitch, width, and height in multiple dimensions, the design achieves effective light extraction without requiring high aspect ratios, thereby simplifying the overall device structure and fabrication process.
3Manufacturing precision
If parallel substrate surfaces are used, then manufacturing precision is maintained, but light extraction efficiency deteriorates due to total internal reflection
Solution Approach 1:
The patent introduces asymmetric pattern features on the substrate surface, such as inclined sides or non-uniform profile shapes, that break the symmetry of total internal reflection. This asymmetric design allows light to escape at multiple angles while maintaining precise control over the pattern geometry through photolithographic fabrication.
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 solution enhances both light extraction efficiency and internal quantum efficiency by allowing for better epitaxial growth quality and reduced heat absorption, thereby improving the overall performance of the light-emitting device.
Implementation Method 1
the light emitted from the active layer 705 to the parallel substrate surface is easily reflected back to the epitaxial stack because of total internal reflection (TIR) effect
Implementation Method 2
the first patterned unit has side surfaces abutting with each other and substantially non-parallel to the first surface in cross-sectional view
Data Source
AI summary
A light-emitting device comprises a substrate having a top surface and a plurality of patterned units protruding from the top surface; and a light-emitting stack formed on the substrate and having an active layer with a first surface substantially parallel to the top surface, wherein one of the plurality of patterned units comprises a plurality of connecting sides constituting a first polygon shape in a top view of the light-emitting device, wherein the one of the plurality of patterned units comprises a vertex and a plurality of inclined surfaces respectively extending from the plurality of connecting sides, the plurality of inclined surfaces commonly joining at the vertex in a cross-sectional view of the light-emitting device, the vertex being between the top surface of the substrate and the first surface of the active layer, and the plurality of inclined surfaces comprises a second polygon shape in the cross-sectional view of the light-emitting device.