InGaN Light Emitting Device Stress Relaxation via AlGaN Buffer
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Solution Overview
Problem
Semiconductor light emitting devices using nitride-based III-V group compound semiconductors face challenges in improving light emitting efficiency due to compressive stress caused by lattice mismatch between the substrate and epitaxially grown layers, leading to distortion in quantum well layers and reduced electrostatic withstand pressure.
Innovation Solution
Incorporating an n-side intermediate layer with a low Al composition ratio AlGaN layer between the multilayered structural body and the light emitting portion to relax compressive stress, combined with a multilayered structural body and light emitting portion using InGaN layers with varying In composition ratios to manage stress and enhance crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a gallium nitride semiconductor light emitting device is formed on a sapphire substrate, then the device can be manufactured, but compressive stress accumulates in the epitaxially grown layer due to thermal expansion coefficient mismatch, causing distortion in the quantum well layer and reducing light emitting efficiency
Solution Approach 1:
An AlGaN buffer layer with graded aluminum composition (gradually increasing from bottom to top) is introduced between the sapphire substrate and the InGaN multilayered structure. This buffer layer acts as an intermediary that progressively adapts the lattice mismatch between the sapphire substrate and the InGaN layers, reducing dislocation density and improving crystalline quality without preventing manufacturing
Solution Approach 2:
The aluminum composition ratio in the AlGaN buffer layer is gradually changed from 0.05 to 0.3 from bottom to top, creating a graded structure that progressively reduces lattice mismatch. This parameter gradient allows the structure to accommodate thermal expansion differences while maintaining high crystalline quality in the InGaN active layers
2Productivity
If the In composition ratio in the well layer is increased to improve light emitting efficiency, then light output increases, but compressive stress and piezoelectric field effects become more pronounced, causing crystal defects
Solution Approach 1:
The patent employs InGaN layers with locally optimized indium composition ratios - the well layers have higher In content (0.03-0.15) for efficient light emission, while the barrier layers have lower or zero In content for stress management. This local differentiation allows high light emitting efficiency in the well layers while the barrier layers provide mechanical stability and reduce piezoelectric field effects
Solution Approach 2:
The structure combines InGaN well layers with GaN barrier layers in a multilayered superlattice. This composite structure leverages the high radiative efficiency of InGaN while using GaN's mechanical strength and low piezoelectric coefficient to counteract compressive stress and prevent crystal defects
3Stress or pressure
If the Al composition ratio in the AlGaN layer is increased to reduce compressive stress, then stress relaxation improves, but light emitting efficiency decreases due to increased piezoelectric field and reduced carrier confinement
Solution Approach 1:
The AlGaN stress management function is segmented into a dedicated buffer layer with graded composition, separate from the InGaN light-emitting multilayered structure. This segmentation allows the buffer layer to handle stress relaxation with higher Al content while the InGaN active structure maintains optimal composition for high light emitting efficiency without excessive piezoelectric fields
4Device complexity
If a single-layer structure is used to simplify device configuration, then manufacturing complexity reduces, but stress management capability and light emitting efficiency deteriorate
Solution Approach 1:
The patent transitions from a single-layer structure to a vertically stacked multilayered superlattice structure. This dimensional organization allows independent optimization of each layer's composition and thickness, enabling simultaneous stress management and high light emitting efficiency that cannot be achieved with a single layer
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 reduces compressive stress, decreases operating voltage, and improves light emitting efficiency by minimizing crystal defects and piezoelectric field influence, resulting in a semiconductor light emitting device with enhanced performance.
Implementation Method 1
an aluminum composition ratio in the AlGaN buffer layer is gradually increased from a bottom surface toward a top surface, the compressive stress can be relaxed
Implementation Method 2
a buffer layer having a graded aluminum composition is formed between the sapphire substrate and the InGaN multilayered structure, so that a lattice mismatch between an InGaN layer and the sapphire substrate can be reduced
Implementation Method 3
This compressive stress causes an accumulation of distortions in a quantum well layer of an active layer, for example. As a result, the influence of piezoelectric field becomes obvious
Data Source
AI summary
According to one embodiment, a semiconductor light emitting device includes n-type and p-type semiconductor layers, a light emitting portion, a multilayered structural body, and an n-side intermediate layer. The light emitting portion is provided between the semiconductor layers. The light emitting portion includes barrier layers containing GaN, and a well layer provided between the barrier layers. The well layer contains Inx1Ga1-x1N. The body is provided between the n-type semiconductor layer and the light emitting portion. The body includes: first layers containing GaN, and a second layer provided between the first layers. The second layer contains Inx2Ga1-x2N. Second In composition ratio x2 is not less than 0.6 times of first In composition ratio x1 and is lower than the first In composition x1. The intermediate layer is provided between the body and the light emitting portion and includes a third layer containing Aly1Ga1-y1N (0<y1≦0.01).