LED Reflector Structure for Higher Light Extraction Efficiency
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Solution Overview
Problem
Conventional light-emitting diodes (LEDs) face low external quantum efficiency due to light absorption by substrates, despite high internal photoelectric converting efficiency, as a large portion of emitted light is absorbed by the substrate, leading to restricted external quantum efficiency.
Innovation Solution
A light-emitting diode structure is developed with a reflecting mirror fabricated between the chip epitaxial layer and the light-absorption substrate, using a high-reflectivity metal mirror and an omnidirectional reflector structure comprising a transparent dielectric layer, a transparent conductive layer, and a metal reflective layer to prevent light absorption and enhance light extraction, including a honeycomb structured surface for increased light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a light-absorption substrate is used for LED growth, then the LED can be fabricated with high internal photoelectric converting efficiency, but a large portion of emitted light is absorbed by the substrate resulting in low external quantum efficiency
Solution Approach 1:
The patent converts the harmful light absorption by the substrate into a beneficial effect by fabricating a high-reflectivity metal mirror on the substrate surface. This mirror reflects the absorbed light back through the LED chip, transforming the energy that would have been lost into useful light output, thereby improving external quantum efficiency while maintaining the advantages of light-absorption substrates for crystal growth
2Productivity
If a reflecting mirror is fabricated between the chip epitaxial layer and the light-absorption substrate, then light extraction efficiency is improved, but the device structure becomes more complex
Solution Approach 1:
The patent optimizes the mirror structure by carefully selecting the metal material (Au, Ag, or Al), controlling the thickness (5-50 nm), and adjusting the pattern design (continuous or discontinuous). These parameter changes enable the mirror to achieve high reflectivity while maintaining compatibility with existing fabrication processes, thus improving light extraction without excessively increasing device complexity
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 proposed structure significantly enhances the light extraction rate and overall luminance of LEDs by reducing internal reflections and absorption, thereby improving external quantum efficiency.
Implementation Method 1
a metal reflective layer is located on one side surface of the transparent conductive layer that is distal from the transparent dielectric layer
Implementation Method 2
refractivity of the transparent dielectric layer is less than that of the light-emitting epitaxial laminated layer and the transparent conductive layer
Data Source
AI summary
A light-emitting diode includes a light-emitting epitaxial layer having a first surface as a light-emitting surface and a second surface opposing the first surface, a first type semiconductor layer, an active layer, and a second type semiconductor layer; a transparent dielectric layer located on the second surface and in direct contact with the light-emitting epitaxial laminated layer, and having conductive through-holes therein; a transparent conductive layer located on one side surface of the transparent dielectric layer that is distal from the light-emitting epitaxial laminated layer; and a metal reflective layer located on one side surface of the transparent conductive layer that is distal from the transparent dielectric layer; wherein the transparent dielectric layer includes a first layer and a second layer; and wherein the first layer is thicker than the second layer, and a refractivity of the first layer is less than a refractivity of the second layer.