LED Structure with Reflective Layer for Light Extraction
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Solution Overview
Problem
Conventional light-emitting diodes (LEDs) suffer from low internal quantum efficiency and reduced brightness due to light being reflected or diffused within the package and absorbed by the pad, resulting in a significant portion of the input power not being converted to light, and the pad obstructing the light path.
Innovation Solution
A high brightness light-emitting diode structure is developed with a reflective layer covering the electrode extensions and pads, ensuring the same thickness for pads and extensions, and using materials with high reflectivity to minimize light absorption and maximize light extraction, comprising a first semiconductor layer, a second semiconductor layer, a light-emitting layer, and reflective layers made of metallic materials or distributed Bragg reflector structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pad is used on the light-emitting diode for wire bonding, then electrical connection is achieved, but light absorption increases and brightness is reduced
Solution Approach 1:
The electrode structure is segmented into three distinct parts: the electrical pad for wire bonding, the extension connecting to the pad, and the reflective layer. This segmentation allows each part to perform its specific function - the pad provides electrical connection, the extension conducts electricity while being covered, and the reflective layer redirects light, thereby resolving the contradiction between maintaining electrical connection and preventing light absorption.
Solution Approach 2:
The reflective layer acts as an intermediary between the extension and the emitted light. Instead of allowing light to directly interact with the light-absorbing pad and extension, the reflective layer intercepts the light and redirects it outward, mediating the interaction between the electrical components and the optical field to prevent harmful light absorption.
2Illumination intensity
If light is emitted from the light-emitting diode, then light output is achieved, but a portion of light is reflected or diffused in the package and absorbed by the pad
Solution Approach 1:
The extension, which necessarily absorbs some light due to its conductivity requirements, is covered with a reflective layer. This converts the potentially harmful light absorption into a beneficial reflection, turning the extension's location into an advantageous position for light redirection. The reflective layer transforms what would be a loss (light absorbed by the extension) into a gain (light reflected outward), effectively converting harm into benefit.
Solution Approach 2:
The reflective layer is applied locally and selectively - it covers the extension but exposes the pad. This local differentiation allows the pad to maintain its electrical connection function while the extension benefits from light reflection. The selective application of the reflective layer creates different optical properties in different locations, optimizing both electrical and optical performance.
3Ease of operation
If the pad obstructs the path of light, then wire bonding is enabled, but brightness is reduced
Solution Approach 1:
The electrode structure is segmented into three distinct parts: the electrical pad for wire bonding, the extension connecting to the pad, and the reflective layer. This segmentation allows each part to perform its specific function - the pad provides electrical connection, the extension conducts electricity while being covered, and the reflective layer redirects light, thereby resolving the contradiction between maintaining electrical connection and preventing light absorption.
Solution Approach 2:
The solution addresses the light path obstruction by adding a vertical dimension - the reflective layer is positioned above the extension in the vertical dimension, creating a three-dimensional structure. This allows light to travel horizontally past the pad while the reflective layer captures and redirects light that would otherwise be absorbed by the extension, effectively using dimensional separation to resolve the contradiction.
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 light extraction efficiency by reflecting light away from the absorption paths, enhancing the brightness of the LED by ensuring that more emitted light is directed outward rather than being absorbed or diffused within the package.
Implementation Method 1
a first reflective layer covering the first extension and exposing the first electrical pad, wherein the reflectivity of the first reflective layer is higher than that of the first extension
Data Source
AI summary
A light-emitting diode structure comprises a first semiconductor layer; a second semiconductor layer under the first semiconductor layer; a light-emitting layer between the first semiconductor layer and the second semiconductor layer for emitting a light; a first electrical pad on the first semiconductor layer for wire bonding; a first extension connecting to the first electrical pad; and a first reflective layer covering the first extension and exposing the first electrical pad, wherein the first electrical pad and the first extension have the same thickness, and the reflectivity of the first reflective layer is higher than that of the first extension.