III Nitride Epitaxial Substrate with Superlattice Buffer for Deep UV Light Output
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Deep ultraviolet light emitting devices grown on sapphire or SiC substrates using existing buffer layer techniques fail to achieve sufficient light output power due to issues with crystallinity and strain buffer effects, leading to reduced light emission efficiency.
Innovation Solution
A III nitride epitaxial substrate is developed with a specific superlattice laminate structure, including an AlN buffer layer and alternating layers of AlxGa1-xN, AlyGa1-yN, and AlzGa1-zN, where the Al content differences between layers are carefully controlled to reduce strain and enhance crystallinity, preventing cracks and absorption of light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a buffer layer is formed on sapphire or SiC substrate to prevent cracks and pits, then crystallinity is improved, but light output power is insufficient due to strain buffer effects and light absorption
Solution Approach 1:
The buffer layer is segmented into a multi-layer superlattice structure with alternating high-Al-content and low-Al-content layers. This segmentation allows different layers to perform different functions: high-Al-content layers provide strain buffer effect to prevent cracks, while low-Al-content layers reduce light absorption, thereby resolving the contradiction between improving crystallinity and enhancing light output power
Solution Approach 2:
Different regions of the buffer layer have different Al contents tailored to local requirements. The high-Al-content layers (AlbGa1-bN where 0.7≤b<1) are positioned where strain compensation is needed, while low-Al-content layers (AlaGa1-aN where 0.03≤a<0.7) are positioned where light transmission is critical, achieving local optimization of both crystallinity and light output
2Strength
If high Al-content layers are used in buffer layer to enhance strain buffer effect, then crack prevention is improved, but light absorption increases reducing emission efficiency
Solution Approach 1:
The buffer layer alternates between high-Al-content layers for strain buffering and low-Al-content layers for light transmission, segmenting the functions to avoid the trade-off between crack prevention and light absorption
Solution Approach 2:
The low-Al-content layers act as intermediary layers between the high-Al-content strain buffer layers and the active layer, mediating the conflict by providing optical transparency while the high-Al-content layers provide mechanical strain compensation
3Strength
If Al content difference between layers is increased to enhance strain buffer effect, then crack prevention is improved, but crystallinity deteriorates due to composition mismatch
Solution Approach 1:
The Al content parameter is optimized within specific ranges (0.03≤a<0.7 for low-Al layers, 0.7≤b<1 for high-Al layers) to balance strain buffer effect and crystallinity. The thickness parameters are also controlled (5-50nm for low-Al layers, 2-20nm for high-Al layers) to ensure proper strain compensation while maintaining good crystallinity
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 substrate structure significantly improves the crystallinity and light output power of deep ultraviolet light emitting devices by effectively managing strain and preventing light absorption, resulting in enhanced emission efficiency.
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
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
Data Source
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 includes a substrate, an AlN buffer layer, a first superlattice laminate, a second superlattice laminate and a III nitride laminate in this order. The III nitride laminate includes an active layer including an AlαGa1-αN (0.03≦α) layer. The first superlattice laminate includes AlaGa1-aN layers and AlbGa1-bN (0.9<b≦1) layers which are alternately stacked, where α(alpha)<a and a<b. The second superlattice laminate includes repeated layer sets each having an AlxGa1-xN layer, an AlyGa1-yN layer, and an AlzGa1-zN (0.9<z≦1) layer, where α(alpha)<x and x<y<z.