AlGaN Epitaxial Wafer Structure for UV Light Extraction
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Solution Overview
Problem
Deep ultraviolet ray emitting diodes face challenges with lattice mismatch defects and high costs due to the use of expensive nitride-based substrates, which hinder efficient light extraction and energy conversion.
Innovation Solution
An epitaxial wafer structure is developed with a transparent and heat-resistant supporting substrate, a seed crystal layer of AlxGa1-xN, and epitaxial layers of AlGaN-based active layers, allowing for light extraction from the substrate side and reducing material costs through the reuse of expensive nitride semiconductor substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an AlN layer is grown on a sapphire substrate or AlN substrate by HVPE method, then the epitaxial substrate provides good crystal quality, but defects due to lattice mismatching are generated which drop internal quantum efficiency and decrease energy conversion efficiency
Solution Approach 1:
The patent changes the material parameter of the substrate from conventional sapphire or ceramic to a GaN-based substrate with lattice constant close to AlN. This parameter change reduces lattice mismatching from significant to minimal, thereby reducing defect generation while maintaining good crystal quality and improving internal quantum efficiency and energy conversion efficiency.
2Reliability
If a GaN single crystal free-standing substrate is used, then the lattice constant is relatively close reducing defects, but the substrate becomes light absorbent which decreases external quantum efficiency
Solution Approach 1:
The patent applies local quality by using different materials for different functional requirements: a GaN-based substrate provides good lattice matching and crystal quality in the active region, while a transparent substrate (sapphire or synthetic quartz) provides light extraction capability at the observation region. This local differentiation resolves the contradiction between lattice matching and light extraction.
3Reliability
If an AlN single crystal free-standing substrate is used, then extremely high-quality epitaxial substrate is achieved, but the substrate is extremely expensive and difficult to manufacture
Solution Approach 1:
The patent replaces the expensive AlN single crystal substrate with cheaper alternatives: GaN-based substrates or transparent substrates (sapphire or synthetic quartz). These cheaper substrates achieve sufficient crystal quality for the application, making the overall device manufacturing more cost-effective while maintaining good epitaxial growth quality.
4Ease of manufacture
If AlN ceramic substrate is used, then inexpensive substrate is achieved, but the substrate is not transparent making it difficult to extract light
Solution Approach 1:
The patent uses transparent substrates (sapphire or synthetic quartz) specifically for the light extraction region where transparency is critical, while using GaN-based substrates where lattice matching is critical. This local differentiation ensures both light extraction efficiency and crystal quality without paying for expensive AlN single crystal throughout the entire structure.
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 achieves high-quality, cost-effective ultraviolet ray emission with improved light extraction efficiency and internal quantum efficiency, making it suitable for sterilization applications.
Implementation Method 1
the seed crystal layer of an AlxGa1-xN (0.5≤x<1) being bonded by laminating to a first supporting substrate
Implementation Method 2
an AlGaN-based active layer
Implementation Method 3
since the AlN ceramic substrate is not transparent, it is difficult to extract light from the substrate side
Data Source
AI summary
An epitaxial wafer for an ultraviolet ray emission device including: a first supporting substrate being transparent for ultraviolet ray and having heat resistance; a seed crystal layer of an AlxGa1-xN (0.5<x≤1) single crystal bonded on the first supporting substrate by laminating; and an epitaxial layer on the seed crystal layer, the epitaxial layer having: a first conductive clad layer containing AlyGa1-yN (0.5<y≤1) as a main component; an AlGaN-based active layer; and a second conductive clad layer containing AlzGa1-zN (0.5<z≤1) as a main component that are stacked and grown in this order. An inexpensive epitaxial wafer for an ultraviolet ray emission device having good light extraction efficiency and high quality and having an epitaxial layer of a III-group nitride such as AlN; and a method for manufacturing the same.