GaN Seed Crystal Substrate with Stripe Projections for Dislocation Control
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Solution Overview
Problem
Existing methods for producing gallium nitride (GaN) crystals using a flux method require a thick seed crystal layer, leading to defects such as dislocations and cracks due to the stair-like micro-steps on the substrate, which limits the quality of the grown crystal.
Innovation Solution
A substrate with an epitaxial seed crystal layer featuring repetitive stripe-shaped projections and recesses, where the projections have a level difference of 0.3 to 40 µm and width of 5 to 100 µm, and recesses with a bottom thickness of 2 µm or more and width of 50 to 500 µm, allowing grain boundaries to form and intersect, thereby reducing dislocation density and thermal stress, resulting in a higher quality GaN crystal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thick seed crystal layer is used to form stair-like micro-steps on the substrate, then the GaN crystal can be grown by the flux method, but dislocation density increases and crystal quality deteriorates
Solution Approach 1:
The seed crystal layer surface is segmented into multiple regions with different heights (first, second, and third regions), creating a stepped structure that allows grain boundaries to form and intersect, thereby stopping dislocation propagation while maintaining a thinner overall seed layer
Solution Approach 2:
The invention transitions from a traditional planar seed crystal layer to a three-dimensional stepped structure with varying heights, introducing vertical dimensionality to control dislocation propagation paths and improve crystal quality without requiring increased thickness
2Reliability
If stair-like micro-steps are formed on the substrate surface, then grain boundaries can be generated to stop dislocation propagation, but thermal stress accumulates causing cracks
Solution Approach 1:
Different regions of the seed crystal layer are assigned different heights and functions: the first region provides initial grain boundary formation, the second region enhances dislocation stopping, and the third region manages thermal stress, with each region optimized for its specific purpose
Solution Approach 2:
The invention controls the height differences between regions within specific ranges (5-20 µm, 2-10 µm, 1-5 µm respectively) to balance dislocation control effectiveness with thermal stress management, preventing crack formation while maintaining dislocation propagation interruption
3Quantity of substance
If the seed crystal layer thickness is reduced, then material usage and production cost decrease, but dislocation density increases due to insufficient grain boundary formation
Solution Approach 1:
The seed crystal layer is divided into multiple height levels that create effective grain boundaries within a thinner overall structure, achieving dislocation control with reduced material consumption compared to traditional thick uniform layers
Solution Approach 2:
The stepped seed crystal layer creates a composite structure with regions of different heights and properties, combining the benefits of grain boundary formation for dislocation control with reduced overall thickness for lower material usage
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 enables the growth of high-quality GaN crystals with reduced dislocation density, inclusions, and cracks, even when the seed crystal layer thickness is minimized, by forming voids that relax thermal stress and stop dislocation propagation, leading to a more uniform and crack-free upper layer.
Implementation Method 1
the seed crystal layer is an epitaxial layer
Implementation Method 2
The underlying substrate including a seed crystal layer of GaN is immersed in a mixed melt containing metallic gallium and metallic sodium, thus causing the GaN crystal to grow on the principal surface of the underlying substrate while nitrogen gas is introduced to the mixed melt
Implementation Method 3
dislocations involved in the seed crystal layer propagate in a direction intersecting an advancing direction of the grain boundary, and the propagation of the dislocation is stopped by the grain boundary at a point where the dislocation and the grain boundary intersect each other
Implementation Method 4
many voids formed at the points where the grain boundaries collide with each other serve to relax thermal stress caused by a difference in thermal expansion between the seed crystal layer of the underlying substrate and the remaining layer
Data Source
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AI summary
An underlying substrate 14 according to an embodiment of the present invention includes a seed crystal layer 16 of a group 13 nitride crystal on a' sapphire substrate 15. Projections 16a and recesses 16b repeatedly appear in stripe shapes at a principal surface of the seed crystal layer 16. The projections 16a have a level difference ha of 0.3 to 40 µm and a width wa of 5 to 100 µm, and the recesses 16b have a bottom thickness tb of 2 µm or more and a width wb of 50 to 500 µm.