LED Strain-Relaxed Layer with Hexagonal-Pyramid Cavities

Solution Overview

Problem

The built-in electric field in light-emitting diodes (LEDs) due to piezoelectric polarizations reduces Internal Quantum Efficiency (IQE) and causes the droop effect, particularly in LEDs with nitride films grown on sapphire substrates, which conventional methods like a single thick InGaN layer fail to adequately address.

Innovation Solution

A light-emitting diode structure is developed with a strain-relaxed layer comprising a strain-absorbed layer with hexagonal-pyramid cavities and a surface-smoothing layer, which effectively reduces strain in the active layer by converting horizontal strain into vertical strain, improving the smoothness and reducing the built-in electric field.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stress or pressure

If a single thick InGaN layer is formed to reduce strain in the active layer, then the strain is reduced, but the surface smoothness deteriorates and the built-in electric field is not adequately reduced

Engineering Contradiction:

Improvestrain in active layerVSAvoidsurface smoothness

Core Design Contradiction:

Stress or pressureVSManufacturing precision

Solution Approach 1:

The strain-relaxed layer is segmented into multiple functional sub-layers: a strain-absorbed layer with hexagonal-pyramid cavities that absorbs strain, and a surface-smoothing layer that restores surface quality. This segmentation allows each sub-layer to perform its specific function independently, resolving the contradiction between strain reduction and surface smoothness maintenance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The strain-absorbed layer contains a plurality of cavities arranged in a hexagonal-pyramid pattern, creating a porous structure that effectively absorbs strain through the cavity walls while maintaining overall layer integrity. This porous architecture provides the strain absorption mechanism without compromising the subsequent surface smoothing process.

Inventive Principle:

Principle #31Porous materials

2Stress or pressure

If a single thick InGaN layer is formed to reduce strain, then strain is reduced, but the built-in electric field remains high causing droop effect

Engineering Contradiction:

Improvestrain in active layerVSAvoiddroop effect

Core Design Contradiction:

Stress or pressureVSLoss of energy

Solution Approach 1:

The strain-relaxed layer is segmented into multiple functional sub-layers: a strain-absorbed layer with hexagonal-pyramid cavities that absorbs strain, and a surface-smoothing layer that restores surface quality. This segmentation allows each sub-layer to perform its specific function independently, resolving the contradiction between strain reduction and surface smoothness maintenance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The strain-absorbed layer contains a plurality of cavities arranged in a hexagonal-pyramid pattern, creating a porous structure that effectively absorbs strain through the cavity walls while maintaining overall layer integrity. This porous architecture provides the strain absorption mechanism without compromising the subsequent surface smoothing process.

Inventive Principle:

Principle #31Porous materials

3Ease of manufacture

If conventional single thick InGaN layer is used, then manufacturing is simple, but IQE is reduced due to built-in electric field

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidInternal Quantum Efficiency

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The strain-relaxed layer is segmented into multiple functional sub-layers: a strain-absorbed layer with hexagonal-pyramid cavities that absorbs strain, and a surface-smoothing layer that restores surface quality. This segmentation allows each sub-layer to perform its specific function independently, resolving the contradiction between strain reduction and surface smoothness maintenance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The strain-absorbed layer contains a plurality of cavities arranged in a hexagonal-pyramid pattern, creating a porous structure that effectively absorbs strain through the cavity walls while maintaining overall layer integrity. This porous architecture provides the strain absorption mechanism without compromising the subsequent surface smoothing process.

Inventive Principle:

Principle #31Porous materials

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 structure enhances the Internal Quantum Efficiency (IQE) and mitigates the droop effect by efficiently reducing strain and built-in electric fields, leading to improved light emission efficiency compared to conventional single thick InGaN layer approaches.

Implementation Method 1

effectively reduces strain in the active layer by converting horizontal strain into vertical strain

Methodology Applied

Scientific EffectStrain conversion: Deformation

Implementation Method 2

a surface-smoothing layer on the strain-absorbed layer, the surface-smoothing layer filling the cavities

Methodology Applied

Scientific EffectFilling: Deposition (physical)

Data Source

PatentUS8653499B2Light-emitting diode with strain-relaxed layer for reducing strain in active layer

Publication Date: 2014.02.18 ENNOSTAR CORP

AI summary

A light-emitting diode (LED) includes a first conductivity type semiconductor layer, a strain-relaxed layer over the first conductivity type semiconductor layer, an active layer over the strain-relaxed layer, and a second conductivity type semiconductor layer over the active layer. The strain-relaxed layer includes a strain-absorbed layer over the first conductivity type semiconductor layer and a surface-smoothing layer on the strain-absorbed layer filling the cavities. The strain-absorbed layer includes a plurality of cavities in a substantial hexagonal-pyramid form.