GaN HEMT Cap Layer Segmentation for Leakage Control
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Solution Overview
Problem
The challenge in stabilizing the characteristics of high electron mobility transistors (HEMTs) with a cap layer containing iron (Fe) arises from Fe diffusion during growth, leading to unstable contact resistance and surface morphology due to Fe's larger ionic radius, making it difficult for Fe to enter the Ga site and remain within the semiconductor structure.
Innovation Solution
A compound semiconductor device structure is implemented with a cap layer comprising a first region doped with Fe and a second region above it, where the Fe concentration in the second region is lower than in the first region, effectively suppressing leakage current and stabilizing the surface morphology by controlling Fe diffusion and distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If Fe is contained in the cap layer to offset donor impurity, then leakage current is reduced, but characteristics of the HEMT become difficult to stabilize
Solution Approach 1:
The cap layer is divided into multiple regions with different Fe concentrations: a first region with higher Fe concentration to offset donor impurity and reduce leakage current, and a second region with lower Fe concentration to maintain stable characteristics. This segmentation allows different portions of the cap layer to perform different functions simultaneously.
Solution Approach 2:
Different regions of the cap layer are assigned different Fe concentrations based on their specific functional requirements. The first region (closer to the barrier layer) has higher Fe concentration for leakage current suppression, while the second region (closer to the surface) has lower Fe concentration for characteristic stability, creating local quality variations throughout the cap layer structure.
2Object-generated harmful factors
If Fe concentration is increased in the cap layer to suppress leakage current, then leakage current is reduced, but surface morphology deteriorates due to Fe diffusion
Solution Approach 1:
The cap layer is segmented into regions with different Fe concentrations, preventing excessive Fe accumulation at the surface while maintaining sufficient Fe content for leakage current suppression. The multi-region structure controls Fe distribution to avoid surface morphology deterioration.
Solution Approach 2:
Fe concentration is optimized locally in different regions: higher concentration in the first region for leakage suppression, and lower concentration in the second region near the surface to maintain good surface morphology. This local quality variation resolves the contradiction between leakage current suppression and surface quality.
3Object-generated harmful factors
If Fe is doped uniformly throughout the cap layer, then leakage current is suppressed, but contact resistance becomes unstable due to Fe diffusion during growth
Solution Approach 1:
The cap layer is divided into multiple regions with different Fe concentrations rather than uniform doping. This segmentation prevents excessive Fe diffusion to specific areas, stabilizing contact resistance while maintaining leakage current suppression through the higher Fe concentration in the first region.
Solution Approach 2:
Different Fe concentrations are applied locally in different regions of the cap layer. The first region has higher Fe concentration for leakage suppression, while the second region has lower Fe concentration to prevent Fe diffusion-related instability, achieving both leakage suppression and contact resistance stability through local quality optimization.
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 stabilizes the characteristics of HEMTs by reducing leakage current and improving surface morphology, enabling better pinch-off characteristics and electron mobility while maintaining sufficient 2DEG density.
Implementation Method 1
the cap layer includes: a first region doped with Fe; and a second region above the first region, a concentration of Fe in the second region being lower than a concentration of Fe in the first region
Implementation Method 2
A cap layer is formed on the barrier layer for improving characteristics such that suppression of current collapse and suppression of gate leakage by relaxing an electric field concentration
Data Source
AI summary
A compound semiconductor device includes: a GaN-based channel layer; a barrier layer of nitride semiconductor above the channel layer; and a cap layer of nitride semiconductor above the barrier layer, wherein the cap layer includes: a first region doped with Fe; and a second region above the first region, a concentration of Fe in the second region being lower than a concentration of Fe in the first region.