Patterned Sapphire Substrate Pyramidal Projections for LED Light Extraction
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Solution Overview
Problem
Previous light emitting diodes (LEDs) face issues with crystal defects and suboptimal light extraction efficiency as output increases, necessitating improvements in crystallinity and light extraction from sapphire substrates.
Innovation Solution
A sapphire substrate with pyramidal projections having side surfaces inclined between 53° and 59° and a height of 1.0 to 1.7 µm, arranged in a triangular lattice pattern, is used to grow nitride semiconductors, enhancing crystallinity and light extraction efficiency by suppressing growth on side surfaces and allowing effective light reflection and diffraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If truncated triangular pyramidal-shaped projections are arranged on sapphire substrate to improve light extraction efficiency, then light extraction efficiency is improved, but crystal defects become apparent and crystallinity deteriorates
Solution Approach 1:
The patent changes the geometric parameters of the projections, specifically setting the inclined angle of side surfaces to 53°-59° and height to 1.0-1.7 µm, which optimizes both light extraction efficiency and crystallinity by controlling light reflection paths and semiconductor growth patterns simultaneously
Solution Approach 2:
The patent creates different surface qualities at different locations: the side surfaces of projections have specific inclined angles that suppress crystal growth and reflect light, while the principal surface between projections allows normal crystal growth, achieving both high crystallinity and light extraction efficiency through localized surface property differentiation
2Loss of energy
If projection height is increased to improve light extraction efficiency, then light extraction efficiency is improved, but voids are generated and crystallinity deteriorates
Solution Approach 1:
The patent establishes an optimal height range of 1.0-1.7 µm for projections, which is sufficient to create effective light reflection and extraction paths while remaining low enough to prevent void formation and maintain crystal structure quality during semiconductor layer growth
3Loss of energy
If side surface inclined angle is adjusted to optimize light reflection, then light extraction efficiency is improved, but crystal growth is affected
Solution Approach 1:
The patent identifies and applies a critical inclined angle range of 53°-59° for projection side surfaces, which creates optimal conditions for both light reflection (improving extraction efficiency) and crystal growth suppression on side surfaces (maintaining growth quality on principal surface)
Solution Approach 2:
The patent creates functional differentiation across the substrate surface: projection side surfaces with specific inclined angles serve light reflection and crystal growth suppression functions, while principal surfaces between projections maintain normal crystal growth conditions, achieving both goals simultaneously through spatial differentiation
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 approach results in nitride semiconductor LEDs with improved crystallinity and light extraction efficiency, particularly from the side opposite to the sapphire substrate and perpendicular to it, reducing crystal defects and increasing luminous and radiant flux ratios.
Implementation Method 1
the inclined angle of the flat inclined surface is set to an angle at which an incident light perpendicular to the base surface is totally reflected at the flat inclined surface
Implementation Method 2
an optical simulation including reflection and refraction used to simulate the light illumination intensity of gallium nitride (GaN)-based light-emitting diodes (LEDs) on varied patterned sapphire substrates
Data Source
Figure 1(a)~2
Figure 3(a)~3(b)
Figure 4~5
AI summary
[Technical Problem] A sapphire substrate and a method for manufacturing the same are provided, which enables growth of a nitride semiconductor having excellent crystallinity and can achieve a nitride semiconductor light emitting element having excellent light extraction efficiency. [Solution to Problem] A sapphire substrate provided with a plurality of projections on a principal surface on which a nitride semiconductor is grown to form a nitride semiconductor light emitting element, wherein the projection is substantially pyramidal-shaped having a pointed top and constituted by a plurality of side surfaces, wherein the side surface has an inclined angle of between 53° and 59° from a bottom surface of the projection, and wherein the side surface is crystal-growth-suppressed surface on which growth of nitride semiconductor is suppressed relative to the substrate surface located between the adjacent projections.