SiC Substrate Off-Angle Optimization for GaN HEMT
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Solution Overview
Problem
Existing group 13 nitride epitaxial substrates for HEMT devices have insufficient electron mobility and surface roughness, leading to suboptimal performance in high-frequency operations.
Innovation Solution
Incorporating an intermediate AlxGa1-xN layer between the AlN nucleation layer and the GaN electron transit layer, along with a SiC base substrate with a (0001) plane off angle of 0.1° to 0.5°, and using a barrier layer composition of InzAl1-zN or AlwGa1-wN to enhance electron mobility and surface quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a GaN-based semiconductor layer is grown on an SiC base substrate with 0° or 0.2° off angle, then sheet resistance variation is reduced, but electron mobility remains insufficient (about 500 cm2V−1s−1) and surface pits are generated
Solution Approach 1:
The patent optimizes the off angle parameter of the SiC base substrate to a specific range (0.1° to 0.5°) to simultaneously achieve low sheet resistance variation and high electron mobility. This parameter optimization resolves the contradiction by finding the optimal value that satisfies both requirements.
Solution Approach 2:
The patent introduces an AlN buffer layer as an intermediary between the SiC base substrate and the GaN semiconductor layer. This intermediate layer mediates the interface between substrate and active layer, improving crystal quality and electron mobility while maintaining the benefits of the optimized off angle substrate.
2Ease of manufacture
If an AlN nucleation layer is formed directly on an SiC substrate with 0.1° off angle, then fabrication is simplified, but surface roughness increases and electron mobility is insufficient
Solution Approach 1:
The patent segments the nucleation process into multiple layers: an AlN buffer layer formed first on the SiC substrate, followed by a GaN layer. This segmentation allows each layer to perform its specific function optimally, with the AlN layer providing a stable foundation and the GaN layer achieving low surface roughness and high electron mobility.
Solution Approach 2:
The AlN buffer layer serves as an intermediary that improves the interface quality between the SiC substrate and the GaN layer. It provides a stable nucleation surface that reduces surface roughness in subsequent layers while maintaining fabrication simplicity through a straightforward sequential deposition process.
3Reliability
If the off angle of the SiC base substrate is increased to improve electron mobility, then sheet resistance variation increases, but if decreased to reduce sheet resistance variation, electron mobility remains insufficient
Solution Approach 1:
The patent identifies and optimizes the off angle parameter to a specific range (0.1° to 0.5°) that simultaneously achieves high electron mobility and low sheet resistance variation. This parameter optimization resolves the contradiction by finding the optimal value that satisfies both requirements.
4Reliability
If a barrier layer with high In or Ga content is used to enhance electron mobility, then surface pits are generated, but if low In or Ga content is used, electron mobility and maximum drain current are insufficient
Solution Approach 1:
The patent optimizes the composition parameter of the barrier layer by controlling the In or Ga content within a specific range. This parameter optimization enhances electron mobility and maximum drain current while preventing surface pit formation, resolving the contradiction between performance and surface quality.
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 configuration achieves significantly improved electron mobility of up to 1300 cm2V−1s−1 and higher maximum drain current, while reducing surface pits and enhancing surface flatness, thereby manufacturing HEMT devices with superior characteristics.
Implementation Method 1
a nucleation layer which is formed on one main surface of the base substrate and is composed of AlN
Implementation Method 2
an electron transit layer which is formed on the nucleation layer and is composed of a group 13 nitride
Data Source
AI summary
Provided is a group 13 nitride epitaxial substrate with which the HEMT device having superior characteristics can be manufactured. This epitaxial substrate is provided with: a base substrate composed of SiC and having a main surface with a (0001) plane orientation; a nucleation layer formed on one main surface of the base substrate and composed of AlN; an electron transit layer formed on the nucleation layer and composed of a group 13 nitride with the composition AlyGa1-yN (0≤y<1); and a barrier layer formed on the electron transit layer and composed of a group 13 nitride with the composition InzAl1-zN (0.13≤z≤0.23) or AlwGa1-wN (0.15≤w≤0.35). The (0001) plane of the base substrate has an off angle of 0.1° or more and 0.5° or less, and an intermediate layer composed of a group 13 nitride with the composition AlxGa1-xN (0.01 ≤x≤0.4) is further provided between the nucleation layer and the electron transit layer.