GaN Growth Substrate Composition for Lattice and CTE Matching
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Solution Overview
Problem
The widespread adoption of gallium nitride (GaN) in power electronics is hindered by the lack of suitable substrates for epitaxial growth, leading to high defect rates and manufacturing challenges due to lattice mismatch and thermal expansion issues with existing substrates.
Innovation Solution
A GaN growth layer or wafer with a bulk region composed of a polycrystalline material having a coefficient of thermal expansion of 2-25 ppm/K, incorporating spinel compounds and TiO2-δ, which can serve as both a substrate and interlayer to minimize curvature and eliminate lattice mismatch, thereby reducing defects in GaN epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional substrates are used for GaN epitaxial growth, then manufacturing is feasible, but high defect rates occur due to lattice mismatch and thermal expansion issues
Solution Approach 1:
The patent introduces a buffer layer comprising a polycrystalline material with spinel compounds (ZnxCd1-x)(CryAl1-y)2O4 and TiO2-δ as an intermediary between the substrate and GaN epitaxial layer. This buffer layer mediates the lattice mismatch and thermal expansion coefficient differences between the substrate and GaN, reducing dislocation propagation and defect formation while enabling feasible manufacturing processes.
Solution Approach 2:
The patent modifies the buffer layer composition parameters by incorporating variable ratios of Zn/Cd and Cr/Al in the spinel compounds, along with sub-stoichiometric TiO2-δ. By adjusting these compositional parameters, the buffer layer's lattice constant and thermal expansion coefficient are optimized to match GaN, thereby reducing defects while maintaining manufacturability.
2Reliability
If substrates with mismatched thermal expansion coefficients are used, then manufacturing is easier, but thermal expansion issues cause high defect rates
Solution Approach 1:
The patent adjusts the thermal expansion coefficient of the buffer layer by modifying the composition parameters x and y in the spinel compounds (ZnxCd1-x)(CryAl1-y)2O4 and the oxygen deficiency δ in TiO2-δ. These parameter changes enable the buffer layer to have a thermal expansion coefficient that closely matches GaN, reducing thermal stress and defect formation during high-temperature epitaxial growth.
3Reliability
If lattice mismatch is not addressed, then substrate selection is simpler, but defect rates increase due to strain in GaN growth layers
Solution Approach 1:
The patent employs a buffer layer with spinel compounds and TiO2-δ as an intermediary structure between the substrate and GaN epitaxial layer. This intermediate layer has a lattice constant that serves as a transition between the substrate and GaN, reducing lattice mismatch and strain while maintaining a manageable layered structure for device fabrication.
4Reliability
If curvature is not minimized in growth layers, then manufacturing is simpler, but strain and defects increase in GaN films
Solution Approach 1:
The patent controls the buffer layer composition parameters (x, y, δ) to optimize its mechanical and thermal properties, enabling the layer to better accommodate thermal stresses during growth and cooling cycles. This parameter optimization minimizes curvature formation in the GaN films while maintaining a practical growth process.
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
This approach minimizes defects and strain in GaN growth layers, enabling higher quality GaN films with reduced curvature and improved thermal expansion matching, thus enhancing the production of GaN-based power electronics.
Implementation Method 1
The bulk region may have a polycrystalline material with coefficient of thermal expansion (CTE) of about 2-25 ppm/K above 800 K... to minimize curvature and eliminate lattice mismatch, thereby reducing defects in GaN epitaxial growth
Data Source
AI summary
A gallium nitride (GaN) growth layer includes a first surface, a second surface, and a bulk region extending between the first and second surfaces, the bulk region having a polycrystalline material with coefficient of thermal expansion (CTE) of about 2-25 ppm/K above 800 K and one or more spinel compounds having formula (I):(ZnxCd1-x) (CryAl1-y)2O4 (I), where x and y are any number between 0 and 1, one of the first and second surfaces including a GaN epitaxial growth region.