InAlN Buffer Layer for Crack-Free GaN Growth on SiC
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Solution Overview
Problem
The existing techniques for growing group III nitride semiconductors on SiC substrates often result in crack formation in the channel layer due to high-quality AlN buffer layers, which affects the crystal quality and performance of GaN-based electronic devices.
Innovation Solution
An epitaxial substrate is developed with a buffer layer composed of Inx1Aly1Gaz1N, featuring a columnar polycrystalline structure with a transition in crystalline grain shape between the lower and upper parts, and a root mean square roughness of 0.2-6 nm, allowing for crack-free growth of functional layers with improved crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an AlN film with excellent crystal quality is used as a buffer layer, then the crystal quality of the GaN film is improved, but cracks are easily generated in the channel layer
Solution Approach 1:
An InAlN layer is introduced as an intermediary between the AlN buffer layer and the GaN channel layer. This intermediate layer has a composition gradient that transitions from high Al content near the AlN buffer to lower Al content near the GaN channel, serving as a stress buffer that prevents crack propagation while maintaining the benefits of the AlN buffer layer for crystal quality
Solution Approach 2:
The composition of the InAlN layer is varied continuously through a composition gradient, changing the aluminum content from higher values near the AlN interface to lower values near the GaN interface. This parameter change allows the layer to accommodate lattice mismatch and thermal expansion differences, reducing stress concentration that would otherwise cause cracking
2Temperature
If an AlN buffer layer is formed on SiC substrate, then heat conductivity is improved, but the lattice mismatch causes stress and cracks
Solution Approach 1:
A composite structure is created with multiple layers: SiC substrate, AlN buffer layer, composition-gradient InAlN transition layer, and GaN channel layer. Each layer contributes different properties - the SiC provides heat conductivity, the AlN provides crystal quality improvement, and the InAlN gradient layer provides stress management, achieving a balance of thermal and mechanical properties
Solution Approach 2:
The InAlN layer exhibits local quality variation through its composition gradient, with different aluminum concentrations at different depths. The region near the AlN buffer has higher Al content to match lattice parameters, while the region near the GaN channel has lower Al content to reduce misfit dislocations, allowing each local region to optimize for its specific function
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 enables the fabrication of high-electron mobility transistors (HEMTs) with excellent characteristics, including mobility of at least 1300 cm2/Vs and drain current of 1000 mA/mm, and further enhanced performance with mobility of 1500 cm2/Vs and reduced gate leakage current.
Implementation Method 1
a buffer layer formed by epitaxially growing on the base and formed of a group III nitride expressed in a composition formula Inx1Aly1Gaz1N
Data Source
AI summary
A buffer layer formed of Inx1Aly1Gaz1N formed on a base, with an upper part of the buffer layer containing columnar polycrystalline including a grain boundary existing in a direction substantially perpendicular to a surface of the base. The number of grain boundaries in the lower part of the buffer layer is greater than that in the upper part, and a full width at half maximum of an X-ray rocking curve of the upper part is 300-3000 seconds, RMS of the surface of the buffer layer is 0.2 nm-6 nm, and the ratio of the grain boundary width of the crystal grain of the upper part in a direction parallel to the base surface to the formation thickness of the buffer layer is 0.5-1.5.