UV LED Stress Adjustment Layer Design
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Solution Overview
Problem
UV light emitting diodes (UV LEDs) face issues with crystallinity and production yield due to cracking caused by thermal and structural deformation, primarily attributed to lattice mismatch and differences in thermal expansion coefficients between the sapphire substrate and AlGaN layers, leading to absorption of UV light and deterioration in luminous efficacy.
Innovation Solution
Incorporating a stress adjustment layer with a multilayer structure and an Al delta layer in the UV LED, which applies compressive stress to prevent tensile stress increase, thereby reducing the likelihood of cracks in semiconductor layers and improving crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If AlGaN layers with 10% or more Al composition are grown on sapphire substrate to achieve UV light emission, then UV light emission capability is improved, but cracking and breaking occur due to thermal and structural deformation
Solution Approach 1:
The patent divides the stress adjustment layer into multiple sub-layers with different Al composition ratios (first nitride layer with higher Al content, second nitride layer with lower Al content). This segmentation allows progressive stress management, where each layer handles a portion of the thermal and structural stress, preventing catastrophic failure while maintaining UV emission capability.
Solution Approach 2:
The patent varies the Al composition ratio parameter across different layers of the stress adjustment layer. The first nitride layer has a higher Al composition ratio (closer to the active layer) while the second nitride layer has a lower Al composition ratio (closer to the n-type layer). This parameter gradient allows optimization of both stress management and UV light emission, as each layer's composition is tailored to its specific functional requirements.
2Loss of energy
If high Al composition ratio nitride semiconductor layers are used to prevent UV light absorption, then luminous efficacy is improved, but lattice mismatch and thermal expansion difference cause wafer bowing and crack generation
Solution Approach 1:
The patent applies different Al composition ratios to different local regions (layers) of the stress adjustment layer. The first nitride layer positioned closer to the active layer has a higher Al composition ratio to optimize UV light emission and prevent absorption, while the second nitride layer positioned closer to the n-type layer has a lower Al composition ratio to better match the lattice structure and reduce thermal stress. This local quality variation allows simultaneous optimization of luminous efficacy and manufacturing precision.
Solution Approach 2:
The stress adjustment layer functions as a composite structure combining nitride layers with different Al composition ratios. This composite approach allows the system to exhibit properties that neither single-layer configuration could achieve alone: the higher-Al layer provides optimal UV emission characteristics while the lower-Al layer provides better lattice matching and stress resistance, collectively preventing wafer bowing and crack generation while maintaining high luminous efficacy.
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 stress adjustment layer effectively prevents crack generation in UV LED semiconductor layers, enhancing production yield and crystallinity, and maintaining luminous efficacy by managing stress and lattice mismatch.
Implementation Method 1
the first stress adjustment layer includes an Al delta layer inserted in the first nitride layer, and a lower surface of the first nitride layer in which the Al delta layer is inserted has greater average tensile stress
Implementation Method 2
This problem is caused by lattice mismatch or a difference in coefficient of thermal expansion between the sapphire substrate and the Al x Ga (1-x) N layer
Implementation Method 3
Due to a difference in coefficient of thermal expansion between the sapphire substrate having a relatively high coefficient of thermal expansion and a nitride semiconductor having a relatively low coefficient of thermal expansion, a wafer suffers from bowing into a concave shape upon growth of the nitride semiconductor at high temperature
Data Source
Figure 1~3a(c)
Figure 3b~3c
Figure 4~5
AI summary
Disclosed herein is a UV light emitting diode. The UV light emitting diode includes a first conductive type semiconductor layer; a first stress adjustment layer disposed on the first conductive type semiconductor layer, and including a first nitride layer including Al and a second nitride layer disposed on the first nitride layer and having a lower Al composition ratio than the first nitride layer; an active layer disposed on the first stress adjustment layer; and a second conductive type semiconductor layer disposed on the active layer, wherein the first stress adjustment layer includes an Al delta layer inserted in the first nitride layer, and a lower surface of the first nitride layer in which the Al delta layer is inserted has greater average tensile stress than a lower surface of the second nitride layer directly disposed on the first nitride layer.