LED Nucleation Layer Patterning for Directional Light Extraction
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Solution Overview
Problem
Light emitting diode (LED) devices with patterned sapphire substrates suffer from low luminance levels and broad angular emission patterns due to light escaping from the sides of the chip, which reduces light extraction efficiency.
Innovation Solution
A nucleation layer comprising a first III-nitride material is deposited on a substrate before patterning, followed by a patterned dielectric layer with features and spaces, and a second III-nitride layer is grown only on the exposed areas, avoiding growth on dielectric sidewalls to enhance light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If side-coating materials are used to prevent light escaping from sides, then angular emission control is improved, but light extraction efficiency deteriorates due to light trapping
Solution Approach 1:
The patent removes the harmful side-coating materials entirely and replaces them with a patterned substrate structure that inherently controls light direction. The microlens array is integrated directly into the substrate, eliminating the need for separate side-coating layers that caused light trapping and reduced extraction efficiency.
Solution Approach 2:
The patent transitions from a planar substrate to a three-dimensional patterned substrate with microlens features. By adding vertical dimensionality through microlens protrusions, the device achieves both angular control and high light extraction efficiency without the trade-off imposed by side-coating materials.
2Shape
If patterned sapphire substrate is used, then light directionality is improved, but luminance level deteriorates due to light loss from side surfaces
Solution Approach 1:
The patent converts the previously harmful light escaping from side surfaces into a beneficial feature by designing microlens structures that intentionally shape and direct this light. The patterned substrate transforms what was considered light loss into controlled directional emission that contributes to overall luminance enhancement.
3Device complexity
If conventional LED structure without lens is used, then device complexity is reduced, but light extraction efficiency deteriorates
Solution Approach 1:
The patent merges the substrate and lens functions into a single integrated structure. The microlens array is formed as an integral part of the substrate through patterning, eliminating the need for separate lens components and reducing overall device complexity while maintaining high light extraction efficiency.
Solution Approach 2:
The patterned substrate performs multiple functions simultaneously: it provides mechanical support, controls light direction through microlens features, and enhances light extraction efficiency. This multi-functionality eliminates the need for additional dedicated lens components.
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 method increases light extraction efficiency and brightness by allowing directional emission without a lens, improving angular directionality and lumen output within a narrow cone.
Implementation Method 1
a nucleation layer comprising a first III-nitride material is deposited on a substrate
Implementation Method 2
a III-nitride layer on the plurality of features and on the plurality of spaces, the III-nitride layer comprising a second III-nitride material
Data Source
AI summary
Described are light emitting diode (LED) devices having patterned substrates and methods for effectively growing epitaxial III-nitride layers on them. A nucleation layer, comprising a III-nitride material, is grown on a substrate before any patterning takes place. The nucleation layer results in growth of smooth coalesced III-nitride layers over the patterns.