GaN LED Patterned Sapphire Substrate Geometry Optimization
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Solution Overview
Problem
The light-extraction efficiency (LEE) of gallium nitride-based light-emitting diodes (LEDs) is limited due to total internal reflection, with existing patterned sapphire substrates not fully optimizing the pattern geometry to enhance light extraction and reduce threading-dislocation density.
Innovation Solution
A patterned substrate with circular patterns of specific diameters and pitches, featuring extruded or subtracted shapes, optimized to achieve a diameter-to-pitch ratio between 2.6/3 and 3/3, and heights within a certain range, enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If patterned sapphire substrates are used to improve light extraction efficiency, then light extraction is enhanced through scattering and multiple reflection, but the pattern geometry is not fully optimized and threading-dislocation density is not sufficiently reduced
Solution Approach 1:
The patent applies parameter changes by optimizing specific geometric parameters of the patterns including diameter (d), pitch (p), height (h), and the ratio d/p. The invention specifies that d/p should be greater than 2.6/3 and less than or equal to 3/3, and height h should be greater than (d/2)-0.10 μm and less than or equal to (d/2)+0.10 μm. These precise parameter optimizations maximize light extraction efficiency while effectively reducing threading-dislocation density during epitaxial layer growth.
2Loss of energy
If the diameter-to-pitch ratio is increased to enhance light extraction, then more light is extracted, but the pattern density and surface area coverage may be reduced
Solution Approach 1:
The patent resolves this contradiction by optimizing the diameter-to-pitch ratio parameter within a specific range (greater than 2.6/3 and less than or equal to 3/3). This optimized ratio achieves the best balance between light extraction efficiency and surface area coverage, allowing maximum light extraction while maintaining adequate pattern density for effective dislocation reduction during epitaxial growth.
3Loss of energy
If pattern height is increased to improve light scattering, then light extraction efficiency is enhanced, but manufacturing complexity and precision requirements increase
Solution Approach 1:
The patent optimizes pattern height parameter h by defining it as greater than (d/2)-0.10 μm and less than or equal to (d/2)+0.10 μm. This precise parameter specification achieves effective light scattering and extraction while maintaining manufacturability. The height is optimized relative to the diameter, creating a scalable parameter relationship that simplifies manufacturing control.
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 optimized patterned substrate significantly improves light extraction efficiency by increasing the fraction of patterned surface area, maximizing light extraction while allowing for flexible epitaxial growth conditions, with peak efficiency achieved within specific height ranges for different diameter-to-pitch ratios.
Implementation Method 1
It is limited by total internal reflection inside the LED semiconductor chip, which typically has a larger refractive index than the surrounding material
Implementation Method 2
Scattering and multiple reflection of the light inside the LED chip can be enhanced with these structures, breaking the TIR condition
Data Source
AI summary
The present invention provides a patterned substrate for gallium nitride-based light emitting diode, comprising: a patterned substrate having patterns, wherein the plurality of patterns are circle type having diameters (d) and the distances between the centers of the patterns are pitches (p), and the cross sections of the patterns are extruded shapes and have heights (h), and wherein the value of [diameter (d)/pitch (p)] is larger than (2.6)/3, and equal or smaller than 3/3.