III-Nitride Epitaxial Substrate with Superlattice Buffer for Deep UV LEDs
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Solution Overview
Problem
Deep ultraviolet light emitting devices using III nitride semiconductors on sapphire or SiC substrates face challenges in achieving high light output power due to crystallinity issues and strain buffer effects from existing buffer layer techniques.
Innovation Solution
A III nitride epitaxial substrate with a specific superlattice structure, including an AlN buffer layer and alternating layers of AlGaN with varying Al content, is used to grow a III nitride laminate, optimizing the Al content difference and layer structure to reduce strain and enhance crystallinity, preventing cracks and absorption of light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a buffer layer is formed on sapphire or SiC substrate to grow III nitride semiconductor layer, then crack formation is prevented through strain buffer effect, but light absorption occurs and light output power is insufficient
Solution Approach 1:
The patent changes the compositional parameters of the buffer layer by using AlGaN with controlled Al content (0.03 ≤ α ≤ 0.3) instead of traditional AlN, and optimizes the superlattice structure parameters (layer thickness, Al content differences) to achieve both strain buffering and reduced light absorption
Solution Approach 2:
The patent creates a composite superlattice buffer layer structure alternating between high Al-content layers (Al b Ga 1-b N, 0.9 ≤ b ≤ 1) and low Al-content layers (Al a Ga 1-a N), combining the advantages of both compositions to simultaneously provide strain buffering and minimize light absorption
2Manufacturing precision
If AlN buffer layer and superlattice structure are used to improve crystallinity, then crack formation is prevented, but device complexity increases
Solution Approach 1:
The patent segments the buffer layer into multiple functional components: an AlN buffer layer for initial strain compensation, followed by a superlattice buffer layer with alternating high and low Al-content layers, each serving specific strain management functions
Solution Approach 2:
The patent applies different Al content compositions at different depths and locations within the buffer layer structure, with high Al-content layers positioned to handle specific strain conditions and low Al-content layers optimized for light transmission, creating locally optimized properties throughout the 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 proposed substrate structure significantly improves the light output power of deep ultraviolet light emitting devices by achieving higher crystallinity and reducing light absorption, while preventing crack formation, thus enhancing the performance of these devices.
Implementation Method 1
there has been a problem in that, if the III nitride semiconductor is grown on the substrate, the grown-up III nitride semiconductor causes cracks and pits (point-like defects). In view of this, it is known that a highly crystalline III nitride layer is grown by forming a buffer layer on a substrate, and then epitaxially growing a III nitride semiconductor layer on the buffer layer, thereby preventing the formation of cracks and pits due to the strain buffer effect of the buffer layer.
Implementation Method 2
the studies made by the inventor of the present invention revealed that sufficient light output power cannot be achieved even if a deep ultraviolet light emitting device is produced by forming a buffer layer disclosed in PTL 1 or PTL 2 on a substrate made of sapphire or SiC instead of a Si substrate and forming a III nitride semiconductor layer on the buffer layer
Implementation Method 3
A III nitride semiconductor is formed by performing epitaxial growth on a substrate made of sapphire, SiC, Si, GaAs, or the like
Data Source
Figure 1
Figure 2A(a)~2A(c)
Figure 2B(a)~2B(c)
AI summary
A III nitride epitaxial substrate which makes it possible to obtain a deep ultraviolet light emitting device with improved light output power is provided. A III nitride epitaxial substrate 10 includes a substrate 12, an AIN buffer layer 14, a first superlattice laminate 16, a second superlattice laminate 18 and a III nitride laminate 20 in this order. The III nitride laminate 20 includes an active layer 24 including an AlαGa1-αN (0.03 ≤ α) layer. The first superlattice laminate 16 includes AlaGa1-aN layers 16A and AlbGa1-bN (0.9 < b ≤ 1) layers 16B which are alternately stacked, where α < a and a < b hold. The second superlattice laminate 18 includes repeated layer sets each having an AlxGa1-xN layer 18A, an AlyGa1-yN layer 18B, and an AlzGa1-zN (0.9 < z ≤ 1) layer 18C, where α < x and x < y < z hold.