Self-Supporting GaN Substrate Defect Reduction
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Solution Overview
Problem
The production of large-area single crystal substrates for light emitting devices is costly and inefficient, with existing substrates like sapphire causing lattice mismatch and thermal expansion issues, leading to high defect densities and limited luminous efficiency.
Innovation Solution
A self-supporting polycrystalline gallium nitride substrate with specific crystal orientation and tilt angles is developed, reducing defect density and enhancing luminous efficiency by aligning gallium nitride-based single crystal grains approximately normal to the substrate with an average tilt angle of 1 to 10°, allowing for higher crystallographic tilt and improved light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sapphire substrate is used to form GaN layers, then the substrate provides mechanical support and insulation, but lattice mismatch and thermal expansion differences cause high dislocation density
Solution Approach 1:
The patent uses a GaN single crystal substrate instead of sapphire, making the substrate material homogeneous with the GaN layers. This eliminates lattice mismatch and thermal expansion differences between substrate and epitaxial layers, thereby reducing dislocation density while maintaining mechanical support.
Solution Approach 2:
The patent creates a copy of the GaN crystal structure in the substrate itself (GaN single crystal substrate), rather than using a different material like sapphire. This self-copying approach ensures perfect lattice matching and eliminates interface defects.
2Manufacturing precision
If a GaN single crystal substrate is used, then lattice matching is improved, but the substrate area is limited and production cost increases
Solution Approach 1:
The patent transitions from growing GaN layers laterally on small single crystal substrates to growing them vertically on large-area single crystal GaN substrates. This dimensional approach enables mass production of large-area substrates while maintaining single crystal quality and lattice matching.
Solution Approach 2:
The patent changes the substrate thickness parameter to 200 μm or greater, enabling large-area substrates to maintain mechanical strength and self-support capability. This parameter change allows cost-effective mass production while preserving single crystal quality.
3Ease of manufacture
If the substrate thickness is reduced to lower cost, then manufacturing cost decreases, but the substrate can no longer support itself
Solution Approach 1:
The patent optimizes the substrate thickness parameter to 200 μm or greater, which is the critical threshold where large-area GaN single crystal substrates gain sufficient mechanical strength to self-support. This parameter optimization enables cost-effective thin substrates that maintain structural integrity.
Data Source
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Figure 3
AI summary
Provided is a self-supporting polycrystalline gallium nitride substrate composed of a plurality of gallium nitride-based single crystal grains having a specific crystal orientation in a direction approximately normal to the substrate. In this self-supporting substrate, the crystal orientations of individual gallium nitride-based single crystal grains as determined from inverse pole figure mapping by electron backscatter diffraction (EBSD) analysis performed on the substrate surface are distributed with various tilt angles from the specific crystal orientation, and the average tilt angle thereof is 1 to 10°. Moreover, the light emitting device of the present invention comprises the foregoing self-supporting substrate and a light emitting functional layer formed on the substrate, wherein the light emitting functional layer has at least one layer composed of a plurality of semiconductor single crystal grains, wherein the at least one layer has a single crystal structure in the direction approximately normal to the substrate. According to the present invention, it is possible to provide a self-supporting polycrystalline gallium nitride substrate having a reduced defect density at the substrate surface. Also, it is possible to provide a light emitting device having a high luminous efficiency by using the self-supporting polycrystalline gallium nitride substrate of the present invention.