GaN Substrate Homo-Epitaxy for Dislocation Reduction
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Solution Overview
Problem
Current methods for producing thick GaN layers with good crystal quality are inefficient, expensive, and prone to material loss due to lattice mismatches and thermal expansion issues, making it difficult to achieve substrates with dislocation densities less than 10^8 dislocations/cm^2 for industrial applications.
Innovation Solution
A process involving transferring a first monocrystal GaN layer onto a supporting substrate, followed by crystal growth of a second GaN layer, and selective chemical etching to remove the substrate, ensuring a thickness of at least 10 micrometers with a dislocation density less than 10^8 dislocations/cm^2, using a supporting substrate with minimal thermal expansion mismatch and a protective coating for enhanced bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If hetero-epitaxy is used to grow GaN layers on sapphire, SiC or silicon substrates, then GaN components can be manufactured, but lattice mismatches and thermal expansion differences generate dislocations and defects that degrade crystal quality
Solution Approach 1:
The patent applies homo-epitaxy instead of hetero-epitaxy, growing GaN layers on GaN substrates rather than on sapphire, SiC, or silicon. This ensures identical lattice parameters and thermal expansion coefficients between substrate and epitaxial layer, eliminating lattice mismatch and thermal stress that cause dislocations and defects, thereby achieving high crystal quality with dislocation densities below 10^8 dislocations/cm²
Solution Approach 2:
The patent uses a GaN template substrate to copy the perfect GaN crystal structure onto the epitaxial layers. By growing GaN on GaN, the crystal lattice is replicated without distortion, maintaining atomic-level precision and preventing the generation of dislocations that would occur with mismatched substrate materials
2Length of stationary object
If the thickness of the epitaxied GaN layer is increased to create thick substrates, then substrate quality improves, but cumulative elastic energy from lattice mismatch causes cracking and makes the layer unusable
Solution Approach 1:
By using homo-epitaxy on GaN substrates, the patent eliminates lattice mismatch between substrate and epitaxial layer, removing the source of cumulative elastic energy that would cause cracking in thick layers. This enables growth of thick GaN substrates with thicknesses exceeding 10 micrometers while maintaining structural integrity and avoiding disasterous failures
Solution Approach 2:
The patent prevents cracking before it can occur by eliminating the root cause - lattice mismatch - through the choice of GaN substrate. This beforehand prevention allows thick GaN layers to be grown without the risk of cumulative stress building up to critical levels that would cause sudden cracking
3Manufacturing precision
If intermediate buffer layers are inserted between supporting substrate and GaN layer to reduce lattice parameter differences, then dislocation density decreases, but manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the need for intermediate buffer layers by directly growing GaN on GaN substrates. This removes the complex multi-layer structure required in hetero-epitaxy, simplifying the manufacturing process while achieving the same or better dislocation density reduction through homogeneous crystal growth
Solution Approach 2:
Instead of trying to adapt GaN to grow on mismatched substrates with buffer layers, the patent inverts the approach by using GaN substrates to grow GaN layers, eliminating the need for adaptation layers and simplifying the entire manufacturing process
4Adaptability or versatility
If selective etching is used to remove the GaAs substrate after ELOG, then the GaN layer can be separated and used as substrate, but additional manufacturing steps and material loss occur
Solution Approach 1:
The patent uses a disposable GaAs sacrificial layer with poor crystal quality that is intentionally designed to be removed. This cheap, temporary structure enables the separation of high-quality GaN layers for substrate use without requiring complex release mechanisms, as the sacrificial layer is simply etched away after serving its purpose during growth
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 method enables the production of high-quality, thick GaN substrates with reduced dislocation density and lower manufacturing costs, avoiding material loss and stress-related defects, while maintaining mechanical strength and crystallographic quality.
Implementation Method 1
transferring a first monocrystal GaN layer onto a supporting substrate
Implementation Method 2
applying crystal growth for a second monocrystal GaN layer on the first layer
Implementation Method 3
removing at least one portion of the supporting substrate
Data Source
AI summary
In some embodiments, the invention relates to a process for making a GaN substrate comprising: transferring a first monocrystal GaN layer onto a supporting substrate; applying crystal growth for a second monocrystal GaN layer on the first layer; the first and second GaN layers thereby forming together the GaN substrate, the GaN substrate having a thickness of at least 10 micrometers, and removing at least one portion of the supporting substrate.