Dielectric Reflective Layers in LED Chips for Light Extraction
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Solution Overview
Problem
Conventional light-emitting diodes (LEDs) suffer from optical losses due to less than 100% reflectivity of existing reflective surfaces, leading to reduced light emission efficiency, particularly from internal reflections and absorption by metal reflectors.
Innovation Solution
The implementation of a light-emitting diode (LED) chip with a first reflective layer comprising a plurality of dielectric layers, including silicon dioxide and silicon nitride, which provides a lower index of refraction than the active LED structure, enhancing total internal reflection and incorporating a second reflective layer and an adhesion layer to improve light reflection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If metal reflectors are used in conventional LEDs, then light reflection is provided, but optical losses occur due to less than 100% reflectivity and absorption by the metal reflector
Solution Approach 1:
The patent changes the material parameter of the reflective surface from metal to dielectric layers with specific refractive indices. The first reflective layer uses dielectric materials (such as silicon dioxide with refractive index ~1.46 or silicon nitride with refractive index ~1.99) that provide lower index of refraction than the active LED structure, enhancing total internal reflection and minimizing absorption losses compared to metal reflectors
Solution Approach 2:
The patent employs a composite structure consisting of multiple dielectric layers with different refractive indices arranged in sequence. This multi-layer dielectric composite provides superior optical performance by combining the benefits of total internal reflection at each interface, achieving high reflectivity without the absorption losses inherent in single-material metal reflectors
2Reliability
If a single dielectric layer is used as reflective surface, then light reflection is enhanced compared to metal, but reflection efficiency is limited by the refractive index difference alone
Solution Approach 1:
The patent segments the reflective function into multiple discrete dielectric layers, each with specific thickness and refractive index properties. This segmentation allows each layer to contribute to the overall reflection efficiency through total internal reflection, achieving superior performance compared to a single layer while maintaining manageable structural complexity
Solution Approach 2:
The patent adds the dimensional aspect of multiple layered structures to the reflective surface design. By stacking dielectric layers with varying refractive indices in the vertical dimension, the system achieves enhanced light reflection efficiency that cannot be obtained with a single-layer approach, effectively using structural dimensionality to overcome material limitations
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 configuration significantly increases light reflection and emission efficiency by minimizing absorption and enhancing the extraction of light, resulting in improved brightness and luminous flux, even across a wide wavelength and angle of incidence range.
Implementation Method 1
provides a lower index of refraction than the active LED structure, enhancing total internal reflection
Implementation Method 2
a first reflective layer adjacent the active LED structure and comprising a plurality of dielectric layers
Data Source
AI summary
A light-emitting diode (LED) chip with reflective layers having high reflectivity is disclosed. The LED chip may include an active LED structure including an active layer between an n-type layer and a p-type layer. A first reflective layer is adjacent the active LED structure and comprises a plurality of dielectric layers with varying optical thicknesses. The plurality of dielectric layers may include a plurality of first dielectric layers and a plurality of second dielectric layers of varying thicknesses and compositions. The LED chip may further include a second reflective layer that includes an electrically conductive path through the first reflective layer. An adhesion layer may be provided between the first reflective layer and the second reflective layer. The adhesion layer may comprise a metal oxide that promotes improved adhesion with reduced optical losses.