Micro-LED Active Layer Structure With Stress Relaxation
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Solution Overview
Problem
Miniaturization of LEDs leads to reduced light emission efficiency due to increased lattice defects and lower internal quantum efficiency, particularly with nitride-based materials like InGaN, which are unsuitable for small-sized LEDs as the indium content increases, causing lattice constant differences and defects.
Innovation Solution
A light emitting device is designed with a stress relaxation layer between a nitride semiconductor layer and an active layer, where the stress relaxation layer has a lattice constant between the nitride semiconductor layer and the active layer, reducing lattice defects and improving light emission efficiency by relieving stress through etching, and using InGaN for the stress relaxation and active layers to emit long-wavelength light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the size of LED is reduced to micro or nano unit, then the miniaturization is achieved, but the light emission efficiency is lowered
Solution Approach 1:
A stress relaxation layer is introduced as an intermediary between the n-type nitride semiconductor layer and the active layer. This intermediate layer has a lattice constant between those of the nitride semiconductor layer and the active layer, serving as a transition that reduces lattice mismatch and minimizes dislocation propagation to the active layer, thereby maintaining light emission efficiency in miniaturized LEDs
Solution Approach 2:
The lattice constant parameter is strategically varied across different layers. The stress relaxation layer is designed with a lattice constant that gradually transitions from the n-type nitride semiconductor layer to the active layer, reducing the abrupt parameter change that causes lattice defects and maintaining efficient light emission in micro-scale devices
2Illumination intensity
If the indium content in nitride-based material is increased to emit long-wavelength light, then the wavelength range is extended, but the lattice constant difference with n-GaN layer increases causing lattice defects
Solution Approach 1:
The stress relaxation layer acts as a mediator that bridges the lattice constant gap between low-indium n-type nitride semiconductor layer and high-indium active layer. This intermediate layer with graded lattice constant reduces the direct interface mismatch, allowing high indium content (up to 20% or more) in the active layer for long-wavelength emission while minimizing lattice defects
Solution Approach 2:
The indium content parameter is progressively increased from the stress relaxation layer to the active layer, creating a graded composition structure. This gradual parameter change prevents sudden lattice constant jumps that would generate dislocations, enabling high indium content for long-wavelength emission while maintaining crystal quality
3Illumination intensity
If phosphide-based material is used for long-wavelength light extraction, then the wavelength range is extended, but the internal quantum efficiency decreases in small-sized LEDs
Solution Approach 1:
The material composition parameter is optimized by using nitride-based semiconductors with controlled indium content (20% or more) instead of phosphide-based materials. This parameter change enables long-wavelength emission while maintaining high internal quantum efficiency in micro-scale LEDs, avoiding the efficiency loss inherent to phosphide materials at small dimensions
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 enhances light emission efficiency by reducing lattice defects and maintaining high efficiency even at smaller sizes, making nitride semiconductor materials suitable for long-wavelength light emission in micro-LEDs.
Implementation Method 1
a stress relaxation layer interposed between the first nitride semiconductor layer and the active layer and having a third lattice constant between the first lattice constant and the second lattice constant
Implementation Method 2
an active layer provided on the first nitride semiconductor layer and having a second lattice constant greater than the first lattice constant, the active layer including a nitride semiconductor material including indium
Data Source
AI summary
A light emitting device includes a light emitting device includes: a first nitride semiconductor layer doped with an n-type dopant and having a first lattice constant; an active layer provided on the first nitride semiconductor layer and having a second lattice constant greater than the first lattice constant, the active layer including a nitride semiconductor material including indium; a stress relaxation layer interposed between the first nitride semiconductor layer and the active layer and having a third lattice constant between the first lattice constant and the second lattice constant, the stress relaxation layer including a nitride semiconductor material including indium; and a second nitride semiconductor layer provide on the active layer and doped with a p-type dopant, wherein the active layer includes: an upper active region provided on an upper surface of the stress relaxation layer, and a side active region provided on a side surface of the stress relaxation layer.