Graded AlInGaN Buffer Layer for Nitride Semiconductor Strain Management
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Solution Overview
Problem
The production of nitride compound semiconductor devices on silicon substrates is complicated by the large difference in thermal expansion coefficients, leading to tensile strains and high defect densities, and existing methods to mitigate this often require additional layers that increase manufacturing effort.
Innovation Solution
A buffer layer with a varying aluminum content is grown on the silicon substrate, where the lateral lattice constant increases in one region and decreases in another, creating a compressive strain that counteracts tensile strain and reduces defect density without the need for additional interlayers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a layer structure with additional masking layers is used to reduce dislocation density, then defect density is reduced, but manufacturing effort increases
Solution Approach 1:
The patent combines the strain management function and defect reduction function into a single buffer layer with graded composition. The buffer layer simultaneously provides compressive strain to counteract thermal expansion mismatch and reduces dislocation density through its specific AlInGaN composition gradient, eliminating the need for separate masking layers while achieving both strain management and defect reduction
Solution Approach 2:
The buffer layer is designed to perform multiple functions: it compensates for thermal expansion differences between silicon and GaN, manages strain in the semiconductor layer sequence, and reduces dislocation density. This multi-functional design eliminates the need for additional specialized layers, reducing manufacturing complexity while maintaining high device quality
2Ease of manufacture
If conventional buffer layers are used, then manufacturing is simple, but defect density remains high due to tensile strain
Solution Approach 1:
The patent employs a buffer layer with graded aluminum and indium content, where the composition parameters vary continuously through the layer thickness. This parameter gradient enables progressive strain management and dislocation filtering, achieving low defect density while maintaining a relatively simple single-layer structure that can be grown using standard MOCVD techniques
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 results in low defect densities and reduced manufacturing effort by effectively managing strain and defect propagation in the semiconductor layer sequence, improving the quality of nitride compound semiconductor devices.
Implementation Method 1
The growth of nitride compound semiconductors on comparatively inexpensive silicon substrates is complicated by a comparatively large difference in the coefficients of thermal expansion of the silicon and the nitride compound semiconductor material. In particular, cooling of the layer system from the growth temperature of around 1000° C. used to grow nitride compound semiconductors to room temperature creates major tensile strains in the GaN.
Implementation Method 2
The buffer layer comprises a material composition which varies in such a way that a lateral lattice constant of the buffer layer increases stepwise or continuously in a first region and decreases stepwise or continuously in a second region, which follows the first region in the growth direction.
Data Source
AI summary
A method is provided for producing a nitride compound semiconductor device. A growth substrate has a silicon surface. A buffer layer, which comprises AlxInyGa1-x-yN with 0≦x≦1, 0≦y≦1 and x+y≦1, is grown onto the silicon surface of the substrate. A semiconductor layer sequence is grown onto the buffer layer. The buffer layer includes a material composition that varies in such a way that a lateral lattice constant of the buffer layer increases stepwise or continuously in a first region and decreases stepwise or continuously in a second region, which follows the first region in the growth direction. At an interface with the semiconductor layer sequence, the buffer layer includes a smaller lateral lattice constant than a semiconductor layer of the semiconductor layer sequence adjoining the buffer layer.