Carbon-Rich Mixed Crystal Layer for Si-Based Nitride Epitaxy
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Solution Overview
Problem
The challenge lies in achieving a nitride semiconductor epitaxial substrate with excellent crystallinity on a Si substrate, as existing methods face difficulties in forming high-quality nitride semiconductor layers due to lattice mismatch and thermal expansion coefficient differences, leading to suboptimal device performance and increased costs.
Innovation Solution
A nitride semiconductor epitaxial substrate is created by incorporating a mixed crystal layer with a high concentration of C and a group III metal element between the Si substrate and the nitride semiconductor epitaxial layer, where the C concentration is at least 1.0×10+21 cm−3 and the transition metal element concentration is at most 5.0×10+16 cm−3, facilitating improved crystallinity through a specific growth process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a nitride semiconductor epitaxial layer is formed directly on a Si substrate, then the manufacturing cost is low and mass production is advantageous, but the crystallinity of the nitride semiconductor epitaxial layer deteriorates due to large lattice mismatch and thermal expansion coefficient difference
Solution Approach 1:
A mixed crystal layer containing Si and a group III metal element is introduced as an intermediary layer between the Si substrate and the nitride semiconductor epitaxial layer. This intermediate layer serves as a transition zone that gradually bridges the lattice mismatch between Si and nitride semiconductor, enabling the formation of high-quality epitaxial layers on cost-effective Si substrates.
Solution Approach 2:
The mixed crystal layer is formed as a composite material combining Si and a group III metal element, creating a gradient structure that transitions from the Si substrate to the nitride semiconductor epitaxial layer. This composite approach allows optimization of both cost and crystallinity by controlling the composition and thickness of the mixed crystal layer.
2Reliability
If the initial layer of nitride semiconductor epitaxial layer is doped with high concentration of C or Fe, then leakage current is reduced and high-frequency characteristics are improved, but the crystallinity of the nitride semiconductor epitaxial layer deteriorates or remains the same
Solution Approach 1:
The mixed crystal layer acts as an intermediary that provides the necessary C or Fe doping to improve leakage current and high-frequency characteristics, while preventing these dopants from degrading the crystallinity of the upper nitride semiconductor epitaxial layer. The intermediate layer absorbs or filters the dopant concentration gradient.
Solution Approach 2:
The doping with C or Fe is localized to the mixed crystal layer rather than being distributed throughout the entire nitride semiconductor epitaxial layer. This local quality approach allows the dopants to provide electrical benefits at the interface while the upper layers maintain high crystallinity for optimal device performance.
3Manufacturing precision
If a single crystal SiC film is disposed on a surface of Si substrate to improve crystallinity, then the crystallinity of nitride semiconductor epitaxial layer is improved, but the device complexity and cost increase greatly
Solution Approach 1:
Instead of using a complete single crystal SiC film, the invention changes the parameters by using a mixed crystal layer with controlled composition and thickness. This parameter change approach achieves the necessary crystallinity improvement while maintaining a simpler structure that is more compatible with mass production on Si substrates.
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 a nitride semiconductor epitaxial substrate with enhanced crystallinity, improving the quality and reliability of nitride semiconductor devices while maintaining cost-effectiveness.
Implementation Method 1
growing a second nitride semiconductor layer above the first nitride semiconductor layer by crystal growth
Implementation Method 2
nitride semiconductor epitaxial layer disposed above the Si substrate
Implementation Method 3
maintaining the temperature of the Si substrate and a temperature of the first nitride semiconductor layer at 900° C. or higher, and diffusing a group III metal element from the first nitride semiconductor layer to the Si substrate
Data Source
AI summary
A nitride semiconductor epitaxial substrate includes: a Si substrate; a nitride semiconductor epitaxial layer disposed above the Si substrate; and a mixed crystal layer disposed between the Si substrate and the nitride semiconductor epitaxial layer, and containing Si and a group III metal element, the mixed crystal layer containing a high concentration of C. The mixed crystal layer has a concentration of at least 1.0×10+21 cm−3, and a transition metal element concentration of at most 5.0×10+16 cm−3.