LED DBR Structure With Low-Carbon Layers for Reduced Absorption
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Solution Overview
Problem
Existing LED reflectors, such as those using TiO2 nanoparticles or metal coatings, suffer from excess stray light absorption and manufacturing difficulties, while amorphous TiO2 layers in DBRs are photocatalytic, leading to significant absorption losses due to carbon contamination from organometallic precursors.
Innovation Solution
A DBR structure with alternating high and low refractive index layers, where the low refractive index layers have low carbon regions formed using halide precursors like AlCl3, reducing carbon content and preventing photocatalytic degradation, and the high refractive index layer is titanium oxide (TiO2), stacked to a thickness of less than 10 microns for improved reflectivity and reduced absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If amorphous TiO2 layers are used in DBR structure, then reflectivity is improved, but photocatalytic degradation occurs leading to absorption losses
Solution Approach 1:
A low refractive index layer with low carbon content is introduced as an intermediary between the high refractive index TiO2 layer and the environment. This intermediary layer prevents direct contact between carbon sources and TiO2, thereby preventing photocatalytic degradation while maintaining the reflectivity benefits of the TiO2 layer.
Solution Approach 2:
The carbon content parameter of the low refractive index layer is specifically controlled to be low. By changing this material parameter, the layer becomes resistant to photocatalytic degradation while still providing the necessary optical properties for the DBR structure.
2Ease of manufacture
If organometallic precursors are used for DBR manufacturing, then ease of manufacture is improved, but carbon contamination increases leading to degradation
Solution Approach 1:
Different regions of the low refractive index layer have different carbon contents. The portion adjacent to the TiO2 layer has low carbon content to prevent degradation, while other portions may have higher carbon content. This local differentiation resolves the contradiction between ease of manufacture and carbon contamination.
Solution Approach 2:
The low refractive index layer is segmented into regions with different carbon contents. This segmentation allows the layer to simultaneously provide ease of manufacture (using organometallic precursors in some regions) and low carbon contamination (using alternative methods in regions adjacent to TiO2).
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 solution significantly reduces absorption losses and enhances light extraction efficiency, maintaining reflectivity while minimizing carbon-related degradation, leading to improved performance and reliability of LED devices, especially under high temperature conditions.
Implementation Method 1
A better reflector is provided by a non-metallic distributed Bragg reflector (DBR). Atomic layer deposition can be used to create multiple layers of precise thickness and of alternating low and high refractive index materials.
Implementation Method 2
Atomic layer deposition can be used to create multiple layers of precise thickness and of alternating low and high refractive index materials.
Implementation Method 3
Unfortunately, amorphous layers of TiO2 created by such ALD processes are photocatalytic. In the presence of blue light generated by an LED and heat, the TiO2 layer can react with carbon contamination from organometallic precursors to create graphite.
Data Source
AI summary
A distributed Bragg reflector (DBR) structure on a substrate includes a high refractive index layer comprising titanium oxide (TiO2) and a low refractive index layer having a high carbon region and at least one low carbon region that contacts the high refractive index layer. Multiple layers of the high refractive index layer and the low refractive index layer are stacked. Typically, the multiple layers of the high refractive index layer and the low refractive index layer are stacked to a thickness of less than 10 microns. Each of the respective layers of the high refractive index layer and the low refractive index layer have a thickness of less than 0.2 microns.