Dielectric Reflective Layer for LED Light Extraction
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Solution Overview
Problem
The reflective layers in lateral type light emitting devices degrade over time, leading to reduced light reflectance and reliability due to the use of metal layers, which have high absorption rates and are sensitive to substrate roughness.
Innovation Solution
A light emitting device package is designed with a reflective layer comprising multiple dielectric layers, including a first dielectric layer with a specific refractive index and a second dielectric layer with a different refractive index, and a second reflective layer with a refractive index similar to air, enhancing reflectance without degrading reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a metal layer is used as the reflective layer at the lower end of the insulating substrate, then the reflectance is initially high, but the reliability degrades over time as the reflectance decreases
Solution Approach 1:
The reflective layer is constructed as a composite structure consisting of multiple dielectric layers with alternating high and low refractive indices. This composite dielectric structure replaces the single-material metal layer, achieving high reflectance through optical interference while maintaining stability and reliability over time.
Solution Approach 2:
The invention changes the material parameter from metal to dielectric, and optimizes the refractive index parameters by using alternating high and low refractive index materials. The thickness of each layer is precisely controlled to be one-quarter of the target wavelength, creating constructive interference for reflected light and achieving high reflectance without the degradation issues of metal layers.
2Illumination intensity
If a metal layer is used as the reflective layer, then the initial reflectance is high, but the absorption rate is also high and reliability is weak
Solution Approach 1:
The reflective layer uses a composite dielectric structure with alternating high and low refractive index materials instead of a single metal layer. This composite structure reduces energy absorption while maintaining high reflectance through optical interference effects, thereby reducing energy loss compared to metal-based reflective layers.
3Illumination intensity
If a metal layer is used as the reflective layer, then the initial reflectance is high, but the reflectance degrades as time elapses
Solution Approach 1:
The reflective layer is constructed as a composite dielectric structure with alternating high and low refractive index materials. This composite structure provides stable optical properties over time and does not suffer from the degradation issues that affect metal layers, thereby maintaining high reflectance for extended periods.
Solution Approach 2:
The invention replaces the metal layer (which degrades over time) with a dielectric layer structure that provides long-term stability. The dielectric materials are inherently more stable and resistant to degradation, ensuring the reflective layer maintains its performance throughout the operational lifetime of the LED device.
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 achieves superior reflectance characteristics comparable to metal reflective layers while maintaining reliability, by using a combination of dielectric layers and an air or low refractive index layer to improve light reflectance and reduce absorption.
Implementation Method 1
a first reflective layer having a plurality of dielectric layers including a first dielectric layer having a first refractive index over the substrate, and a second dielectric layer having a second refractive index different from the first refractive index over the first dielectric layer
Implementation Method 2
When forward voltage is applied to the LED, electrons of an n layer are combined with holes of a p layer, so that energy corresponding to an energy gap between a conduction band and a valance band may be generated. This energy is realized as heat or light, and the LED emits the energy in the form of light.
Data Source
AI summary
Disclosed are a light emitting device, a light emitting device package, and a lighting system. The light emitting device includes a light emitting structure including a first conductive semiconductor layer, an active layer and a second conductive semiconductor layer; a substrate over the light emitting structure; a first reflective layer having a plurality of dielectric layers including a first dielectric layer having a first refractive index over the substrate, and a second dielectric layer having a second refractive index different from the first refractive index over the first dielectric layer; and a second reflective layer over the first reflective layer, the second reflective layer having a refractive index lower than the refractive index of each dielectric layer of the first reflective layer.