Lattice-Constant Epitaxial Template for UV LED Strain Management
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Solution Overview
Problem
Existing UV LEDs face challenges with low light output efficiency due to lack of lattice-matched substrates for AlGaN-based devices, leading to strain management issues and poor light extraction efficiency, with biaxial compression or tension causing dislocations and surface cracks, and limited light extraction efficiency due to UV absorbing layers and refractive index differences.
Innovation Solution
A lattice constant formatted epitaxial template with alternately arranged protrusions and depressions is used, where first and second material portions with different lattice constants are grown, allowing for strain modulation and improved light extraction by forming an n-type layer and active region on this template, which breaks down large-area strain into localized opposite-sign strains, reducing dislocation and crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thick AlN template is used to maintain high structural quality, then structural quality is improved, but biaxial compression increases causing dislocation generation and surface roughness
Solution Approach 1:
The patent segments the previously uniform thick AlN template into alternating thin AlN layers and AlGaN superlattice layers. This segmentation allows the total thickness to be maintained for structural quality while distributing the strain burden across multiple interfaces, preventing dislocation generation and surface roughness that would occur in a single thick layer.
Solution Approach 2:
The patent creates a composite structure by combining AlN layers with AlGaN superlattice layers to form an epitaxial template. This composite material approach allows optimization of each component's properties - AlN provides structural stability while AlGaN manages strain - resolving the contradiction between maintaining structural quality and preventing dislocations.
2Reliability
If AlN/AlGaN superlattice is applied for strain management, then dislocation generation is reduced, but light extraction efficiency remains limited due to refractive index differences
Solution Approach 1:
The patent modifies the lattice constant parameter by incorporating InGaN layers with different lattice constants into the epitaxial template. This parameter change creates localized regions with varying lattice constants that can better match the AlGaN active region, improving light extraction efficiency while maintaining the strain management benefits of the superlattice structure.
3Reliability
If p-GaN or p-InGaN contact layer is employed for ohmic contact, then electrical contact is achieved, but UV light is absorbed reducing light extraction efficiency
Solution Approach 1:
The patent introduces an AlGaN electron-blocking layer as an intermediary between the p-type contact layer and the active region. This intermediary layer has the dual function of providing good electrical contact while being transparent to UV light, thus resolving the contradiction between achieving ohmic contact and maintaining light extraction efficiency.
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 enhances internal quantum efficiency and light extraction efficiency of UV LEDs by reducing strain energy and defect density, enabling coherent growth of thick layers without defects and improved electron injection into the active region.
Implementation Method 1
lattice constants of the first material portions are different from those of the second material portions... breaks down large-area strain into localized opposite-sign strains
Implementation Method 2
enabling coherent growth of thick layers without defects
Data Source
AI summary
A lattice constant formatted epitaxial template for light emitting devices includes a starting epitaxial template having a base, a plurality of alternately arranged protrusions and depressions on the base; first material portions epitaxially formed on top of the protrusions and second material portions epitaxially formed in the depressions, wherein lattice constants of the first material portions on the protrusions are different from those of the second material portions in the depressions. A method for making a lattice constant formatted epitaxial template is provided. Also provided is a light emitting device containing a lattice constant formatted epitaxial template.