Double-Sided GaN Seed Crystal for Flat Substrates
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Solution Overview
Problem
Conventional methods for growing GaN substrates, such as ammonothermal growth, result in small-sized crystals with defects that replicate and cause strain gradients, leading to wafer curvature and poor device performance due to lattice mismatch and thermal expansion coefficient differences between the substrate and epitaxial layer.
Innovation Solution
A seed crystal with a large, flat area is produced through double-sided deposition of crystalline materials on a foreign substrate, ensuring epitaxial relationships and similar lattice constants on both sides to minimize strain gradients and defects, using techniques like MOCVD or MBE, and subsequent processing to achieve high-quality, flat substrates for ammonothermal growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ammonothermal growth techniques are used, then high quality crystalline material is obtained, but the crystal size remains small and not useful for commercial applications
Solution Approach 1:
The invention transitions from conventional single-sided seed growth to double-sided seed crystal growth, utilizing both surfaces of a substrate simultaneously. This dimensional approach allows the crystal to expand in multiple directions at once, dramatically increasing the final crystal size while maintaining the high quality characteristics enabled by the ammonothermal process
2Productivity
If heteroepitaxial growth on foreign substrates is used, then GaN films can be grown, but high defect densities result due to lattice mismatch and thermal expansion differences
Solution Approach 1:
The invention employs substrate materials with lattice constants and thermal expansion coefficients that are substantially matched to GaN (within 5%). This homogeneity in material properties between substrate and epitaxial layer eliminates the lattice mismatch and thermal expansion differences that cause defects in conventional heteroepitaxial growth, enabling high-quality GaN film production
3Ease of manufacture
If conventional single-sided deposition is used, then crystal growth can proceed, but strain gradients and wafer curvature occur due to thermal expansion coefficient differences
Solution Approach 1:
The invention deliberately creates asymmetric compensation by depositing crystalline material on both the front and back surfaces of the substrate. This dual-sided deposition generates opposing strain gradients that balance each other, preventing the wafer curvature and bowing that would otherwise occur from thermal expansion mismatches during the growth process
4Productivity
If defects are present in the seed material, then ammonothermal growth can proceed, but defects replicate on the grown crystal structures
Solution Approach 1:
The invention performs preliminary preparation of the seed crystal by depositing high-quality crystalline material on both surfaces before initiating ammonothermal growth. This pre-preparation ensures that the seed crystal itself is free of defects, preventing defect replication during the subsequent growth process and enabling production of defect-free bulk GaN crystals
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 method provides high-quality, flat GaN substrates with reduced dislocation densities and strain gradients, enabling large-area, cost-effective production suitable for commercial applications in devices like light emitting diodes and integrated circuits.
Implementation Method 1
a first thickness of first crystalline material is formed overlying the first surface of the crystalline substrate material... a second thickness of second crystalline material is formed overlying the second surface of the crystalline substrate material... both having epitaxial relationships with the crystalline substrate material
Data Source
AI summary
A high-quality, large-area seed crystal for ammonothermal GaN growth and method for fabricating. The seed crystal comprises double-side GaN growth on a large-area substrate. The seed crystal is of relatively low defect density and has flat surfaces free of bowing. The seed crystal is useful for producing large-volume, high-quality bulk GaN crystals by ammonothermal growth methods for eventual wafering into large-area GaN substrates for device fabrication.