Engineered Substrate for GaN Epitaxial Growth
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Solution Overview
Problem
Heteroepitaxial growth of gallium nitride based LED structures on sapphire substrates results in reduced uniformity and adverse effects on electronic/optical properties due to material mismatch, leading to a need for improved epitaxial growth processes and substrate structures.
Innovation Solution
A substrate structure comprising a polycrystalline ceramic core encapsulated with multiple layers, including tetraethyl orthosilicate, polysilicon, silicon nitride, and silicon oxide, designed to match the coefficient of thermal expansion of epitaxial layers and prevent impurity diffusion, facilitating epitaxial growth with improved uniformity and properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heteroepitaxial growth is used to grow gallium nitride LED structures on sapphire substrates, then LED devices can be manufactured, but the uniformity and electronic/optical properties of the epitaxial layers are reduced
Solution Approach 1:
The patent introduces an engineered substrate structure with intermediate layers between the sapphire substrate and the gallium nitride epitaxial layers. This intermediate structure acts as a mediator that bridges the material mismatch, providing a gradual transition in lattice constants and coefficients of thermal expansion, thereby reducing dislocation density and improving the quality of the epitaxial growth
Solution Approach 2:
The patent employs a composite substrate structure consisting of multiple materials with different properties (sapphire, buffer layers, and gallium nitride layers) arranged in a specific configuration. This composite structure combines the advantages of each material to achieve both mechanical stability and optimal epitaxial growth conditions, resolving the contradiction between manufacturability and layer quality
2Manufacturing precision
If multiple encapsulating layers are added to the substrate structure to match thermal expansion and block impurities, then epitaxial growth uniformity is improved, but the substrate structure complexity increases
Solution Approach 1:
The patent divides the substrate structure into multiple functional segments or layers, each with a specific thickness and material composition. This segmentation allows precise control over thermal expansion matching and impurity blocking while maintaining a systematic and manufacturable structure. Each layer serves a specific function, making the overall complex structure manageable and reproducible
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 engineered substrate structure ensures thermal expansion matching and impurity blocking, enhancing the uniformity and performance of epitaxial layers in optical, electronic, and optoelectronic applications, with reduced diffusion of impurities during high-temperature epitaxial growth processes.
Implementation Method 1
Encapsulating layers utilized as components of the engineered substrate structure block diffusion of impurities present in central portions of the substrate from reaching the semiconductor processing environment
Implementation Method 2
engineered substrate structure that is CTE matched to gallium nitride based epitaxial layers suitable for use in optical, electronic, and optoelectronic applications
Data Source
AI summary
A substrate includes a polycrystalline ceramic core; a first adhesion layer encapsulating the polycrystalline ceramic core; a conductive layer encapsulating the first adhesion layer; a second adhesion layer encapsulating the conductive layer; a barrier layer encapsulating the second adhesion layer, and a bonding layer coupled to the barrier layer, and a substantially single crystalline silicon layer coupled to the bonding layer.