GaN Semiconductor Buffer Structure for Dislocation Reduction
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Solution Overview
Problem
The growth of Group III-V or II-VI semiconductors with cubic or hexagonal crystal lattice structures on substrates with different lattice parameters leads to crystalline defects like dislocations, which are not adequately reduced by existing buffer layer structures, limiting the quality and thickness of the semiconductor layers and their ability to withstand stress and thermal expansion differences.
Innovation Solution
A semiconductor structure with alternating stacks of second and third layers, where the gallium ratio varies to maintain a constant average lattice parameter, interspersed with a relaxation layer, allowing for improved stress management and reduced dislocation density, enabling thicker, higher-quality semiconductor layers with enhanced voltage withstand and reduced leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN is grown directly on silicon or sapphire substrate, then the growth process is simple, but important crystalline defects such as dislocations are generated due to lattice parameter and CTE differences
Solution Approach 1:
The patent introduces an AlN buffer layer as an intermediary between the silicon substrate and GaN layer. This buffer layer has a lattice parameter intermediate between silicon and GaN, reducing the lattice mismatch and serving as a nucleation layer that prevents dislocation propagation from the substrate to the GaN layer.
Solution Approach 2:
The patent segments the interface between substrate and GaN into multiple layers with gradually changing composition (AlN buffer layer followed by AlGaN layers with increasing Ga content). This segmentation allows progressive adaptation from the substrate lattice to the GaN lattice, reducing sudden stress and dislocation formation.
2Ease of manufacture
If a single AlN buffer layer is used, then the growth process is simple, but the thickness of good quality GaN that can be obtained is very limited
Solution Approach 1:
The patent divides the buffer structure into multiple segments: an AlN buffer layer followed by multiple AlGaN layers with progressively increasing Ga content. Each layer segment serves as a transition zone, allowing the GaN layer to be grown thicker without accumulating excessive stress or dislocations.
Solution Approach 2:
The patent changes the compositional parameter of the buffer layers by using AlGaN layers with gradually increasing Ga content. This parameter change allows the lattice parameter to transition smoothly from AlN to GaN, enabling thicker GaN growth while maintaining structural integrity and managing stress.
3Length of stationary object
If GaN layer is made thick on silicon substrate, then the semiconductor functionality is improved, but the GaN layer cracks due to difference in coefficients of thermal expansion during cooling
Solution Approach 1:
The patent changes the compositional parameter of the buffer layers to create a gradient structure where AlGaN layers have progressively increasing Ga content. This parameter change allows the structure to accommodate thermal expansion differences by providing a gradual transition in material properties, preventing crack formation in thick GaN layers during cooling.
Solution Approach 2:
The patent creates a composite buffer structure consisting of AlN and AlGaN layers with different compositional ratios. This composite structure combines the advantages of different materials to manage both lattice mismatch and thermal expansion differences, enabling thick GaN growth without cracking.
4Ease of manufacture
If existing buffer layer structures are used, then the manufacturing process is simple, but the dislocation density in GaN layer is not sufficiently reduced
Solution Approach 1:
The patent segments the buffer structure into multiple thin AlGaN layers with progressively increasing Ga content, separated by AlN layers. Each interface between layers acts as a dislocation filter, and the gradual compositional change prevents dislocation propagation, significantly reducing dislocation density in the final GaN layer.
Solution Approach 2:
The patent introduces a compositional dimension to the buffer structure by varying the Ga content in AlGaN layers. This additional compositional dimension allows for progressive lattice matching and creates multiple interfaces that filter dislocations, reducing dislocation density more effectively than simple thickness variation.
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 structure achieves better semiconductor quality and stress management, allowing for thicker layers with improved voltage resistance and reduced leakage currents, while minimizing the total thickness of the layers, thus reducing manufacturing costs and increasing wafer robustness.
Implementation Method 1
the ratio of a semiconductor element in the second layers varies and increases from one second layer to the next along a direction from the substrate to the first layer, and the ratio of said semiconductor element in the third layers varies and decreases from one third layer to the next along said direction such that a value of an average lattice parameter of each group of adjacent second and third layers is approximately constant
Implementation Method 2
a relaxation layer, allowing for improved stress management and reduced dislocation density
Implementation Method 3
GaN can be grown by hetero-epitaxy on a substrate with a different nature such as a silicon or sapphire substrate
Data Source
AI summary
A semiconductor structure (100) comprising:a substrate (102),a first layer (106) of AlxGayIn(1-x-y)N disposed on the substrate,stacks (107, 109) of several second and third layers (108, 110) alternating against each other, between the substrate and the first layer,a fourth layer (112) of AlxGayIn(1-x-y)N, between the stacks,a relaxation layer of AIN disposed between the fourth layer and one of the stacks, and, in each of the stacks:the level of Ga of the second layers increases from one layer to the next in a direction from the substrate to the first layer,the level of Ga of the third layers is constant or decreasing from one layer to the next in said direction, the average mesh parameter of each group of adjacent second and third layers increasing from one group to the next in said direction,the thickness of the second and third layers is less than 5 nm.