Group III Nitride Semiconductor Light-Emitting Device Strain Relaxation
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Solution Overview
Problem
Conventional Group III nitride semiconductor light-emitting devices face challenges in relaxing stress applied to the light-emitting layer, leading to poor crystallinity and reduced emission output due to lattice constant mismatch and generated piezoelectric fields.
Innovation Solution
A Group III nitride semiconductor light-emitting device is designed with a strain relaxation layer formed of a superlattice structure, including InGaN and GaN layers, where the InGaN layer proximal to the light-emitting layer has a higher In compositional proportion, gradually changing lattice constants to reduce stress and improve crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a light-emitting layer is formed directly on a lower layer with different lattice constant, then device structure is simplified, but stress accumulates and crystallinity deteriorates
Solution Approach 1:
The patent introduces a strain relaxation layer composed of multiple InGaN layers with different In compositional proportions arranged in a superlattice structure. This segmentation approach divides the stress management function into multiple discrete layers, where each layer contributes to gradual stress relaxation while maintaining overall structural integrity and good crystallinity.
Solution Approach 2:
The strain relaxation layer acts as an intermediary layer between the lower layer and the light-emitting layer. By positioning this layer with graded In compositional proportions in the middle, it mediates the lattice constant mismatch and reduces stress accumulation, preventing direct contact between the light-emitting layer and the highly mismatched lower layer.
2Reliability
If InGaN layer with high In compositional proportion is placed proximal to light-emitting layer, then stress relaxation is improved, but risk of misfit dislocation increases
Solution Approach 1:
The patent applies local quality by varying the In compositional proportion in different InGaN layers within the strain relaxation layer. Layers closer to the light-emitting layer have higher In compositional proportions for better stress relaxation, while layers farther away have lower proportions to reduce misfit dislocation risk. This spatial variation in composition optimizes both stress relaxation and structural integrity locally.
Solution Approach 2:
The patent changes the In compositional proportion parameter across different layers of the strain relaxation layer. By gradually increasing the In compositional proportion from layers farther from the light-emitting layer to those closer to it, the patent achieves continuous stress relaxation while controlling lattice mismatch and minimizing misfit dislocations through parameter optimization.
3Object-generated harmful factors
If stress is applied to light-emitting layer, then piezoelectric field is generated, but emission output is reduced
Solution Approach 1:
The patent converts the harmful stress effect into a beneficial outcome by introducing a strain relaxation layer that intentionally introduces controlled strain through graded In compositional proportions. This controlled strain relaxation prevents the accumulation of harmful stress in the light-emitting layer, thereby reducing unwanted piezoelectric fields and improving emission output through indirect stress management.
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 effectively relaxes stress in the light-emitting layer, enhancing light emission performance and crystallinity, resulting in improved optical and electrical properties.
Implementation Method 1
lattice constant gradually changes in the strain relaxation layer from a layer on the side of a substrate to a layer on the side of the light-emitting layer
Implementation Method 2
strain is relaxed at the boundary between the strain relaxation layer and the light-emitting layer
Implementation Method 3
A piezoelectric field is generated in the layer to which stress is applied
Implementation Method 4
each layer formed through epitaxial growth exhibits good crystallinity
Data Source
AI summary
The present invention provides a Group III nitride semiconductor light-emitting device which is intended to relax stress applied to a light-emitting layer. The light-emitting device includes an MQW layer, and an n-side superlattice layer formed below the MQW layer. The n-side superlattice layer is formed by repeatedly depositing layer units, each unit including an InGaN layer, a GaN layer, and an n-GaN layer which are sequentially deposited from the side of the sapphire substrate. In the n-side superlattice layer, an InGaN layer more proximal to the MQW layer has a higher In compositional proportion. The In compositional proportion of the InGaN layer (which is most proximal to the MQW layer) of the n-side superlattice layer is 70% to 100% of the In compositional proportion of the InGaN layer (which is most proximal to the n-side superlattice layer) of the MQW layer.