LED Substrate Concave-Convex Patterns for Light Extraction
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Solution Overview
Problem
Concave-convex patterns on substrates for LEDs can enhance light extraction efficiency but often cause crystal defects in the epitaxial semiconductor layer.
Innovation Solution
The formation of concave-convex patterns with specific facet angles and shapes on the substrate, using wet etching to stabilize crystal planes and reduce lattice mismatch, allowing for improved crystal quality and light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If concave-convex patterns are formed on the substrate to improve light extraction efficiency, then light extraction efficiency is improved, but crystal defects increase in the epitaxial semiconductor layer
Solution Approach 1:
The patent applies local quality by creating concave-convex patterns with specific facet geometries (e.g., 60-degree angles for sapphire substrates) in localized regions. The convex portions have controlled facet angles that match the crystal orientation of the epitaxial layer, providing locally optimized growth conditions that reduce dislocation density while maintaining light extraction enhancement in the patterned regions.
Solution Approach 2:
The patent changes geometric parameters of the concave-convex patterns, specifically controlling the facet angles to match crystallographic orientations (e.g., 60 degrees for sapphire). By optimizing these angular parameters and the depth-to-width ratio of the patterns, the invention achieves a balance where light extraction is improved without introducing excessive crystal defects during epitaxial growth.
2Loss of energy
If conventional concave-convex patterns are used, then light extraction is enhanced, but manufacturing complexity increases due to additional process steps
Solution Approach 1:
The patent merges the concave-convex pattern formation with the existing substrate preparation process. By using standard photolithography and etching techniques that are already part of the LED fabrication workflow, the invention integrates the light extraction enhancement structure creation into the base process sequence, minimizing additional manufacturing steps while achieving the desired geometric patterns.
Solution Approach 2:
The concave-convex patterns are formed on the substrate before epitaxial growth begins. This preliminary structuring of the substrate surface allows the subsequent epitaxial layers to conformally follow the patterned geometry, achieving light extraction enhancement without requiring post-growth processing steps or complex in-situ pattern formation during the multi-step epitaxial sequence.
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 increases light extraction efficiency while minimizing crystal defects, leading to enhanced performance and reliability of LEDs.
Implementation Method 1
using wet etching to stabilize crystal planes and reduce lattice mismatch
Implementation Method 2
facets that are crystal planes
Data Source
AI summary
Provided are a substrate having concave-convex patterns, a light-emitting diode (LED) including the substrate, and a method of fabricating the LED. The LED includes a substrate, and concave-convex patterns disposed in an upper surface of the substrate and having convexes and concaves defined by the convexes. Unit light-emitting device having a first conductive semiconduct or layer, an active layer, and a second conductive semiconductor layer disposed on the substrate in sequence is present.