LED Chip Electrode Pad Design for Current Spreading
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Solution Overview
Problem
GaN-based LED chips face issues with reduced light emitting area and efficiency due to the formation of electrode pads and extensions, which cause current crowding and optical loss, leading to deterioration in light emitting efficiency and external quantum efficiency, especially at high current densities.
Innovation Solution
The LED chip design includes a semiconductor stack with electrode pads and extensions configured to prevent reduction in light emitting area, using insulation layers and distributed Bragg reflectors to relieve current crowding and minimize optical loss, with transparent conductive layers and current blocking layers to enhance current spreading and reduce absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If electrode pads and extensions are formed on the semiconductor layer, then current spreading is enhanced, but light emitting area is reduced
Solution Approach 1:
The electrode extensions are configured to extend in multiple directions (first extensions in first direction, second extensions in second direction) from the electrode pad, creating a three-dimensional current distribution network that spreads current more effectively across the semiconductor layer without requiring excessive planar area coverage
Solution Approach 2:
The electrode extensions are strategically positioned and dimensioned to provide localized current spreading only where needed near the electrode pad, rather than covering the entire semiconductor layer, thus maintaining light emitting area in regions where current spreading is not critical
2Reliability
If electrode pads and extensions are formed using metal materials, then electrical conductivity is improved, but optical loss increases due to light absorption
Solution Approach 1:
The electrode structure employs a composite material system with a highly conductive metal layer (silver or aluminum) combined with a transparent conductive oxide layer (indium tin oxide, zinc oxide, or aluminum zinc oxide), where the transparent layer reduces optical absorption while the metal layer provides the necessary electrical conductivity
Solution Approach 2:
The patent optimizes the thickness parameters of both the metal layer and transparent conductive oxide layer to achieve a balance between electrical conductivity and optical transparency, with the transparent layer thickness specifically controlled to minimize light absorption while maintaining adequate electrical performance
3Productivity
If electrode extensions are used to enhance current spreading, then current distribution is improved, but current crowding still occurs at regions near the extensions causing optical loss
Solution Approach 1:
The electrode extensions are divided into multiple discrete extension structures (first extensions and second extensions) rather than a single continuous structure, which segments the current flow paths and distributes current more evenly across different regions, preventing concentration at any single point
Solution Approach 2:
The electrode extension configuration is designed to dynamically adapt current distribution by providing multiple extension directions and varying extension lengths, allowing current to naturally distribute along the path of least resistance across different regions of the semiconductor layer
4Strength
If Cr material is used as underlying layer for electrode pads, then adhesion is improved, but reflectivity decreases causing severe optical loss
Solution Approach 1:
The electrode structure uses a composite layered approach where Cr serves as a thin adhesion promoter layer bonded to the metal layer, while the dominant light-interacting layers are highly reflective metals (silver or aluminum) combined with transparent conductive oxides, thus maintaining adhesion functionality while minimizing optical absorption
Solution Approach 2:
The Cr layer is applied only as a thin underlying layer specifically where adhesion is needed at the interface between the metal electrode material and the semiconductor substrate, rather than as a thick continuous layer, thus providing necessary adhesion while minimizing its impact on overall optical reflectivity
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 design effectively prevents current crowding and optical loss, maintaining high light emitting efficiency and external quantum efficiency even at high current densities by optimizing current spreading and reducing absorption, thereby enhancing the overall performance of the LED chip.
Implementation Method 1
an insulation layer interposed between the first electrode pad and the second conductive type semiconductor layer
Implementation Method 2
transparent conductive layers and current blocking layers to enhance current spreading and reduce absorption
Implementation Method 3
GaN based light emitting diodes (LEDs) have been used in a wide range of applications
Data Source
AI summary
Disclosed herein is an LED chip including electrode pads. The LED chip includes a semiconductor stack including a first conductive type semiconductor layer, a second conductive type semiconductor layer on the first conductive type semiconductor layer, and an active layer interposed between the first conductive type semiconductor layer and the second conductive type semiconductor layer; a first electrode pad located on the second conductive type semiconductor layer opposite to the first conductive type semiconductor layer; a first electrode extension extending from the first electrode pad and connected to the first conductive type semiconductor layer; a second electrode pad electrically connected to the second conductive type semiconductor layer; and an insulation layer interposed between the first electrode pad and the second conductive type semiconductor layer. The LED chip includes the first electrode pad on the second conductive type semiconductor layer, thereby increasing a light emitting area.