GaN Buffer Layer Segmentation for Crack Suppression
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Solution Overview
Problem
Nitride semiconductor elements, such as gallium nitride (GaN) semiconductors, face issues like current collapse, reduced breakdown voltage, and increased leakage current due to pits and cracks in the buffer layer, which deteriorate with thicker layers intended to improve breakdown voltage.
Innovation Solution
A semiconductor device structure with a thick buffer layer comprising alternately stacked AlN and C-GaN layers, where the C-GaN layer has a lower carbon concentration than the C-GaN layers in the first and second stacked portions, interposed between them to reduce pit and crack formation while maintaining high breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the buffer layer is thickened to improve breakdown voltage, then breakdown voltage is improved, but pits or cracks occur more easily and become larger in size
Solution Approach 1:
The buffer layer is divided into multiple sub-layers with different thicknesses and compositions. Specifically, it includes a first buffer layer (30 nm-1 μm), a second buffer layer (1 μm-3 μm), and a third buffer layer (3 μm-10 μm), each with optimized properties to prevent crack propagation while maintaining high breakdown voltage.
Solution Approach 2:
Different regions of the buffer layer have different compositions and thicknesses tailored to local requirements. The first buffer layer near the substrate has higher Al content for stress management, while the third buffer layer near the channel has lower Al content and higher thickness for voltage blocking, optimizing both reliability and performance locally.
2Reliability
If the buffer layer is thickened to suppress current collapse, then current collapse is suppressed, but front surface states deteriorate due to pits or cracks
Solution Approach 1:
The buffer layer structure is designed in advance with progressively thicker layers moving away from the substrate. The third buffer layer closest to the channel portion is made thickest (3 μm-10 μm) before channel formation, ensuring that when the channel is later created, the surface state is already optimized and free from defects that would exist in a uniformly thick buffer.
Solution Approach 2:
The buffer is segmented into three distinct layers with progressively different thicknesses and compositions, allowing the region near the channel (third buffer layer) to have optimal surface state while the overall buffer remains thick enough to suppress current collapse.
3Strength
If a thick buffer layer is used to improve breakdown voltage, then breakdown voltage increases, but leakage current increases due to pits or cracks
Solution Approach 1:
The buffer layer is segmented into three layers with progressively increasing thickness, where each layer acts as a barrier to defect propagation. This segmentation prevents pits and cracks from forming continuous leakage paths across the entire buffer thickness, maintaining low leakage current while achieving high breakdown voltage.
Solution Approach 2:
The buffer layer uses a composite structure with varying AlGaN compositions and thicknesses. This composite design creates multiple interfaces that block defect propagation and reduce leakage current paths, while the overall thick structure maintains high breakdown voltage capability.
Data Source
AI summary
A semiconductor device includes a first stacked portion above a substrate, the first stacked portion comprising a first nitride semiconductor layer containing aluminum and a second nitride semiconductor layer containing carbon, a third nitride semiconductor layer on the first stacked portion, the third nitride semiconductor layer containing carbon and having a greater thickness than each of the first and second nitride semiconductor layers, the third nitride semiconductor layer having a lower carbon concentration than the second nitride semiconductor layer, a second stacked portion on the third nitride semiconductor, the second stacked portion comprising a fourth nitride semiconductor layer containing aluminum and a fifth nitride semiconductor layer containing carbon, a sixth nitride semiconductor layer on the second stacked portion, a seventh nitride semiconductor layer on the sixth nitride semiconductor layer and containing aluminum, and a first electrode on the seventh nitride layer.