Inverted LED Substrate Geometry for Light Extraction
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Solution Overview
Problem
Conventional light-emitting diodes experience reduced brightness and luminous efficiency due to light absorption from total internal reflection and critical angle issues, leading to inefficient light emission.
Innovation Solution
A light-emitting device with a transparent substrate and a transparent adhesive layer, where the ratio of the second surface area to the light-emitting layer area is optimized to minimize light absorption, incorporating a multi-layer epitaxial structure and electrodes, and a method of forming these devices to enhance brightness by adjusting the substrate's surface areas and angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflective layer is added between the multi-layer epitaxial structure and the substrate to reflect light downward, then light emission is improved, but light beams with larger incident angles are gradually absorbed by the light-emitting layer due to total internal reflection, reducing brightness and luminous efficiency
Solution Approach 1:
The patent inverts the conventional substrate position by bonding the multi-layer epitaxial structure to the bottom surface of the transparent substrate rather than the top surface. This inversion changes the light extraction path, allowing light to escape through the sides and top of the device without passing repeatedly through the light-emitting layer, thereby reducing absorption losses while maintaining brightness
Solution Approach 2:
The patent transitions from conventional planar light extraction to three-dimensional light emission by bonding the epitaxial structure to the bottom surface of the transparent substrate. This enables light to be extracted in multiple directions (upward through the transparent substrate and sideways), reducing the impact of total internal reflection and improving overall light extraction efficiency
2Productivity
If the substrate area is increased to allow more light extraction paths, then luminous efficiency improves, but the device size and complexity increase
Solution Approach 1:
By inverting the bonding configuration and attaching the epitaxial structure to the bottom surface of the transparent substrate, the patent enables effective light extraction without requiring an oversized substrate. The inversion creates favorable geometry for light escape through the transparent substrate's top and side surfaces, achieving high luminous efficiency with a compact device footprint
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 improves the brightness of light-emitting diodes by reducing light absorption and increasing luminous efficiency through strategic surface area ratios and angles, allowing more light to be emitted without passing through the light-emitting layer.
Implementation Method 1
a transparent adhesive layer on the transparent substrate
Implementation Method 2
a multi-layer epitaxial structure on the transparent adhesive layer, the multi-layer epitaxial structure including a light-emitting layer
Implementation Method 3
When the light from the light-emitting layer 131 is reflected at the bottom of the transparent substrate 120 and travels to the sides of the transparent substrate 120, some light beams (such as light R3) would be reflected back inside the light-emitting diode because its incident angle θ1 is larger than the critical angle θc
Data Source
AI summary
A light-emitting device includes a transparent substrate, a transparent adhesive layer on the transparent substrate, a first transparent conductive layer on the transparent adhesive layer, a multi-layer epitaxial structure and a first electrode on the transparent conductive layer, and a second electrode on the multi-layer epitaxial structure. The multi-layer epitaxial structure includes a light-emitting layer. The transparent substrate has a first surface facing the transparent adhesive layer and a second surface opposite to the first surface, wherein the area of the second surface is larger than that of the light-emitting layer, and the area ratio thereof is not less than 1.6.