Nitride Semiconductor Buffer Layer for Crack-Free Thick Growth
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Solution Overview
Problem
Semiconductor substrates face limitations in crystallinity and thickness due to lattice constant and thermal expansion coefficient mismatches between growth substrates and compound semiconductor layers, leading to dislocation generation and cracking, which hinder the growth of high-quality, thick semiconductor layers for electronic devices.
Innovation Solution
Incorporating a buffer layer with step regions of varying aluminum content and a heterogeneous region to maximize compressive strain, reduce dislocation generation, and control stress, while using mask layers to guide dislocations horizontally and prevent vertical movement, thereby enhancing crystallinity and preventing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a compound semiconductor layer is grown on a growth substrate, then electronic devices can be fabricated, but dislocations are generated due to lattice constant mismatch, decreasing crystallinity
Solution Approach 1:
The buffer layer is divided into multiple step regions with different aluminum concentrations (first step region with lower Al, second step region with higher Al), creating a graded structure that progressively accommodates lattice mismatch and reduces dislocation generation
Solution Approach 2:
Different regions of the buffer layer have different aluminum concentrations tailored to specific functions: the first step region provides a transition zone, while the second step region provides compressive strain, with each region optimized for its local role in dislocation control
2Reliability
If a thick compound semiconductor layer is grown, then high-quality electronic devices can be produced, but cracks occur due to strain from thermal expansion coefficient mismatch
Solution Approach 1:
The buffer layer with step regions is prepared in advance to accumulate compressive strain during growth, which compensates for the tensile strain that develops during cooling, preventing cracks before they occur in the thick semiconductor layer
Solution Approach 2:
The aluminum concentration in the buffer layer is varied across different step regions to control the amount of compressive strain, with the second step region having higher Al content to provide the necessary strain compensation for thick layer growth
3Stress or pressure
If the amount of Al in the buffer layer is increased to control strain, then compressive strain is enhanced, but the complexity of the buffer layer structure increases
Solution Approach 1:
The buffer layer is segmented into a finite number of step regions (first and second step regions) with discrete aluminum concentration levels, providing controlled strain management without excessive structural complexity
Solution Approach 2:
Each step region has a specific aluminum concentration optimized for its location: the first step region has lower Al for transition, and the second step region has higher Al for compressive strain, creating a simplified yet effective graded structure
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 solution enables the growth of thick, crack-free nitride semiconductor layers with improved crystallinity, ensuring the stability of both the semiconductor layer and the growth substrate, thus facilitating the production of high-quality electronic devices like solar cells and light-emitting devices.
Implementation Method 1
the differences in the lattice constants and the thermal expansion coefficients between the growth substrate and the compound semiconductor layer cause strain. That is, a balance between compressive strain during the growth of compound semiconductors and tensile strain during cooling to room temperature after the growth does not match
Implementation Method 2
the differences in the lattice constants and the thermal expansion coefficients between the growth substrate and the compound semiconductor layer cause strain
Implementation Method 3
crystallinity may be decreased by the generation of dislocations caused by the difference in the lattice constants between the growth substrate and the compound semiconductor layer
Data Source
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AI summary
Provided is a semiconductor substrate including a seed layer disposed on a substrate, a buffer layer disposed on the seed layer, a plurality of nitride semiconductor layers disposed on the buffer layer, and at least one stress control layer between the plurality of nitride semiconductor layers. The buffer layer includes a plurality of step regions and at least one heterogeneous region. The plurality of step regions includes the same nitride semiconductor material. The heterogeneous region includes a different nitride semiconductor material from the step regions.