AlInGaN Strain Release Layer for GaN LED Epitaxy
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Solution Overview
Problem
The existing manufacturing processes for light emitting diodes (LEDs) using Distributed Bragg Reflectors (DBR) face issues with lattice mismatch, thermal coefficient differences, and strain-related defects, leading to crack generation and reduced epitaxial layer quality due to the combination of gallium nitride and aluminum gallium nitride materials.
Innovation Solution
Incorporating an aluminum indium gallium nitride (AlInGaN) strain release layer before forming the DBR and modifying the epitaxy process to form the DBR last, with the DBR being directly formed between the metal mirror and the buffer layer, which is composed of alternating layers of aluminum nitride and gallium nitride, and using a bonding substrate with a conductive bonding layer to reduce strain and enhance epitaxy quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If gallium nitride and aluminum gallium nitride are combined to form DBR, then lighting efficiency is enhanced, but lattice mismatch and thermal coefficient differences cause cracks and defects in the epitaxial layer
Solution Approach 1:
An aluminum indium gallium nitride (AlInGaN) strain release layer is introduced as an intermediary between the GaN-based epitaxial layer and the AlGaN/GaN DBR structure. This intermediate layer has lattice constant and thermal expansion coefficient values that are intermediate between the two materials, thereby reducing the lattice mismatch and thermal coefficient differences, and preventing crack generation while maintaining the high lighting efficiency of the DBR
Solution Approach 2:
The invention changes the material composition parameters by using AlInGaN with specific indium content to achieve a lattice constant and thermal expansion coefficient that are intermediate between GaN and AlGaN. This parameter adjustment reduces the stress and strain in the epitaxial layer, preventing defect formation while maintaining the optical performance of the DBR
2Illumination intensity
If DBR is formed using epitaxy method, then lighting efficiency is improved, but large tensile strain causes epitaxial layer to generate cracks
Solution Approach 1:
The AlInGaN strain release layer is formed preliminarily before depositing the AlGaN/GaN DBR structure. This preliminary action creates a buffer that can accommodate the tensile strain that will develop during subsequent epitaxial growth, preventing crack formation in the epitaxial layer while allowing the DBR to be formed with the necessary strain for high lighting efficiency
3Ease of manufacture
If silicon substrate is used for LED growth, then manufacturing cost is reduced, but wafer strain problem leads to crack generation
Solution Approach 1:
The AlInGaN strain release layer serves as a mediator between the silicon substrate and the GaN-based epitaxial structure. This intermediate layer accommodates the lattice mismatch and thermal expansion differences between silicon and GaN, reducing wafer strain and preventing crack generation while maintaining the cost advantage of using silicon substrates
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 effectively reduces film crack issues and enhances the epitaxial quality of the DBR, improving the overall lighting efficiency of the LED without affecting other epitaxial layers, and allows for the efficient formation of the DBR structure without strain accumulation.
Implementation Method 1
the combination of these two materials may also bring great lattice mismatch and thermal coefficient differences, consequently may facilitate generating cracks or defects in the epitaxial layer
Implementation Method 2
the combination of these two materials may also bring great lattice mismatch and thermal coefficient differences
Implementation Method 3
The Distributed Bragg Reflector (DBR) often has been used in the nitride-based LED structure for enhancing the lighting efficiency of the light emitting diode
Implementation Method 4
the material of the bonding layer is selected from the adhesive material formed of silver paste, spontaneous conductive polymer or polymer doped with a conductive material
Data Source
AI summary
The present invention relates to a light emitted diode (LED). The LED includes a metal mirror, a bonding substrate, a distributed bragg reflector (DBR), a buffer layer, and a LED epitaxial structure. The bonding substrate is arranged under the metal mirror. The DBR is arranged on the metal mirror. The buffer layer is arranged on the DBR. The LED epitaxial structure is arranged on the buffer layer.