LED Current Spreading Layer for Light Extraction and Electrical Conductivity

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Solution Overview

Problem

Light emitting diodes (LEDs) face challenges in improving light extraction efficiency while maintaining electrical characteristics due to the high sheet resistance of the second conductive semiconductor layer, which requires current spreading layers like ITO or ZnO, but forming concavo-convex patterns on this layer can degrade electric characteristics.

Innovation Solution

A light emitting device structure that includes a support substrate, a planar layer, a wafer bonding layer, a current spreading layer, a second conductive semiconductor layer, an active layer, and electrode layers, with a reflective layer to enhance light extraction and improve electrical characteristics by forming a stable mechanical bonding force and effective current injection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a current spreading layer is added to reduce sheet resistance, then electrical characteristics improve, but device structure becomes more complex and manufacturing difficulty increases

Engineering Contradiction:

Improveelectrical characteristicsVSAvoiddevice structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the current spreading function and light extraction function into a single integrated structure. The current spreading layer is designed with a specific refractive index range (1.7-2.5) that enables both electrical current spreading and optical light extraction, eliminating the need for separate functional layers and simplifying the overall device structure while maintaining both electrical and optical performance

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The current spreading layer is designed to perform multiple functions simultaneously: it serves as an electrical current spreading path to reduce sheet resistance, and as an optical light extraction interface due to its specific refractive index properties. This multi-functionality reduces the total number of layers needed in the LED structure

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Productivity

If a concavo-convex pattern is formed on the second conductive semiconductor layer to improve light extraction, then light efficiency improves, but electrical characteristics deteriorate

Engineering Contradiction:

Improvelight efficiencyVSAvoidelectrical characteristics

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces a separate current spreading layer positioned between the second conductive semiconductor layer and the active layer. This segmentation allows the second conductive semiconductor layer to maintain its electrical function without pattern disruption, while the current spreading layer provides the light extraction interface with appropriate refractive index properties

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The current spreading layer acts as an intermediary layer that mediates between the electrical requirements of the second conductive semiconductor layer and the optical requirements for light extraction. It provides both electrical current spreading pathways and optical refractive index contrast for efficient light extraction without requiring patterns on the semiconductor layer itself

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If the second conductive semiconductor layer is used directly, then device structure is simple, but sheet resistance is too high for effective current spreading

Engineering Contradiction:

Improvedevice structureVSAvoidsheet resistance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The current spreading layer serves as an intermediary between the power supply and the second conductive semiconductor layer, providing low-resistance current pathways. This intermediary layer has high electrical conductivity to ensure effective current spreading while maintaining a simple overall device structure without requiring complex modifications to the semiconductor layers

Inventive Principle:

Principle #24Intermediary (Mediator)

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 enhances both electrical characteristics and light efficiency of the LED by improving current injection and light extraction, while maintaining the stability of the semiconductor layers.

Implementation Method 1

a wafer bonding layer over the planar layer

Methodology Applied

Scientific EffectWafer bonding: Welding

Implementation Method 2

the LED requires a current spreading layer including ITO (indium tin oxide) or ZnO (zinc oxide) to form an ohmic contact interface

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 3

a reflective layer to enhance light extraction

Methodology Applied

Scientific EffectLight reflection: Reflection

Data Source

PatentUS8471239B2Light-emitting element and a production method therefor

Publication Date: 2013.06.25 BOE HC SEMITEK LTD (HENGQIN)

AI summary

Disclosed is a light emitting device. The light emitting device includes a support substrate; a planar layer over the support substrate; a wafer bonding layer over the planar layer; a current spreading layer over the wafer bonding layer; a second conductive semiconductor layer over the current spreading layer; an active layer over the second conductive semiconductor layer; a first conductive semiconductor layer over the active layer; a first electrode layer over the first conductive semiconductor layer; and a second electrode layer over the current spreading layer.