Ground Substrate With Porous Corundum Layer for GaN Epitaxy
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Solution Overview
Problem
Existing semiconductor devices using GaN and α-Ga2O3 suffer from significant crystal defects due to lattice constant mismatches with sapphire substrates, which hinder the development of high dielectric breakdown electric field characteristics required for power semiconductor applications.
Innovation Solution
A ground substrate with an orientation layer composed of a material having a corundum-type crystal structure with an a-axis and/or c-axis length larger than sapphire, incorporating pores, is used for crystal growth of nitride or oxide of Group 13 elements to reduce crystal defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single-crystal substrate is formed by heteroepitaxial growth on a sapphire substrate, then crystal growth of GaN and α-Ga2O3 can be achieved, but crystal defects occur due to lattice constant mismatch with sapphire
Solution Approach 1:
The patent introduces an orientation layer as an intermediary between the sapphire substrate and the GaN/α-Ga2O3 semiconductor layer. This orientation layer has a corundum-type crystal structure with lattice constants that serve as a transitional bridge, reducing the lattice mismatch stress and preventing crystal defects from propagating to the semiconductor layer, thereby improving both crystal quality and dielectric breakdown characteristics
Solution Approach 2:
The patent applies different crystal structures and lattice constants to different layers: the sapphire substrate maintains its original structure, the orientation layer has a corundum-type structure with specific lattice parameters, and the semiconductor layer has its own crystal structure. This local optimization of crystal structure in each layer resolves the lattice mismatch problem while maintaining the functional requirements of each component
2Stability of the object's composition
If the a-axis length and c-axis length of sapphire are used, then the substrate structure is stable and well-defined, but the lattice constant mismatch with GaN and α-Ga2O3 causes crystal defects
Solution Approach 1:
The patent changes the lattice parameters of the orientation layer from the standard sapphire values (a-axis: 4.754 Å, c-axis: 12.990 Å) to expanded values (a-axis: 4.754-4.983 Å, c-axis: 12.990-13.433 Å). This parameter adjustment creates a better lattice match with GaN and α-Ga2O3 while maintaining the corundum-type crystal structure stability, thereby reducing crystal defects
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 proposed substrate significantly reduces crystal defects, enabling the formation of high-quality semiconductor layers with improved orientation and dielectric breakdown characteristics.
Implementation Method 1
the single crystal substrate is generally formed by heteroepitaxial growth on a sapphire substrate having different lattice constants from those of these materials
Implementation Method 2
the a-axis length (4.754 Å) of sapphire (α-Al2O3) and the a-axis length (4.983 Å) of α-Ga2O3 differ by about 5%, and this difference is the main cause of crystal defects
Implementation Method 3
a plurality of pores are present in the orientation layer... significantly reduced crystal defects (dislocations) in the orientation layer
Data Source
AI summary
Provided is a ground substrate includes an orientation layer used for crystal growth of a nitride or oxide of a Group 13 element. The front surface of the orientation layer on the side used for the crystal growth is composed of a material having a corundum-type crystal structure having an a-axis length and/or c-axis length larger than that of sapphire. A plurality of pores are present in the orientation layer.