III-N Semiconductor Buffer Layer Strain Control
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Solution Overview
Problem
The growth of III-N semiconductor materials on silicon substrates is hindered by lattice constant and thermal expansion coefficient differences, leading to strain and potential cracking, and existing buffer layers compromise insulation properties by narrowing the bandgap.
Innovation Solution
A superlattice structure layer composed of AlGaN and InAlN materials is used as a buffer layer, with each superlattice unit having a thickness of 30 nm or less, an average lattice constant between the silicon substrate and the gallium nitride cap layer, and a thickness ratio of the second layer to the first layer ranging from 1:10 to 10:1, grown using MBE or MOCVD to control strain and maintain high bandgap energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the average lattice constant is adjusted to match gallium nitride by decreasing Al composition or increasing AlGaN layer thickness, then lattice constant continuity is improved, but the bandgap is narrowed and insulation properties deteriorate
Solution Approach 1:
The patent employs a composite superlattice structure consisting of alternating AlGaN and InAlN layers. This composite material approach allows the buffer layer to simultaneously achieve lattice constant continuity (by adjusting the proportion of InAlN layers) and maintain high bandgap energy (by utilizing the wide bandgap properties of both AlGaN and InAlN materials), thereby resolving the contradiction between manufacturing precision and reliability.
Solution Approach 2:
The superlattice structure introduces local compositional variations through alternating layers of different materials (AlGaN and InAlN) with different lattice constants and bandgap energies. By controlling the thickness and composition of each layer locally, the structure achieves overall lattice constant continuity while maintaining high bandgap properties in each individual layer, thus resolving the contradiction between lattice matching and insulation properties.
2Ease of manufacture
If III-N materials are grown on silicon substrates, then cost and substrate availability are improved, but strain and cracking occur due to lattice constant and thermal expansion differences
Solution Approach 1:
The patent introduces a superlattice buffer layer as an intermediary structure between the silicon substrate and the GaN cap layer. This intermediate layer gradually transitions the lattice constant from silicon to GaN through alternating AlGaN and InAlN layers, effectively mediating the strain caused by lattice constant and thermal expansion differences, thereby enabling successful growth of III-N materials on cost-effective silicon substrates while maintaining structural strength.
Solution Approach 2:
The superlattice structure utilizes parameter changes in material composition (varying Al and In content in AlGaN and InAlN layers) and layer thickness to progressively adjust the lattice constant and thermal expansion properties. This gradual parameter transition through multiple layers reduces strain accumulation, allowing the use of inexpensive silicon substrates while preventing cracking and maintaining structural integrity.
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 effectively controls strain and maintains high bandgap energy, preventing bending or cracking and enhancing insulation properties in III-N semiconductor structures.
Implementation Method 1
The average lattice constant in buffer layers may be determined considering lattice constants of the lower and the upper layers so that bending or cracking in the semiconductor structure can be controlled
Implementation Method 2
strain can be controlled between a lower layer (silicon substrate or aluminum nitride seed layer) and an upper layer (gallium nitride layer)
Implementation Method 3
The seed layer, the superlattice structure layer, and the cap layer may be grown by molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD)
Data Source
AI summary
Disclosed herein are a III-N semiconductor structure manufactured by growing a III-N material on a superlattice structure layer, formed of AlGaN and InAlN materials, which serves as a buffer layer, and a method for manufacturing the same. The disclosed III-N semiconductor structure includes: a substrate including a silicon material; a seed layer formed on the substrate and including an aluminum nitride (AlN) material; a superlattice structure layer formed by sequentially depositing a plurality of superlattice units on the seed layer; and a cap layer formed on the superlattice structure layer and including a gallium nitride (GaN) material, wherein the superlattice units are each composed of a first layer including an AlxGa1-xN wherein 0≤x≤1 and a second layer including an InyAl1-yN wherein 0y≤0.4.