Fe-Doped GaN Buffer Layer Segmentation for Leakage Control
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Solution Overview
Problem
Nitride semiconductor HEMTs face challenges with off-state leakage current due to Fe diffusion, which degrades electron mobility and increases on-resistance, while attempts to suppress diffusion through AlGaN layers compromise crystallinity.
Innovation Solution
A semiconductor crystal substrate structure is developed with a first Fe-doped buffer layer and a second undoped GaN buffer layer formed at lower growth temperatures, where the Fe concentration is higher in the first buffer layer and carbon concentration is higher in the second buffer layer, to suppress Fe diffusion without degrading crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the buffer layer is doped with Fe to suppress off-state leakage current, then the resistance of the buffer layer increases, but Fe diffuses upward to the 2DEG region causing increased on-resistance and reduced electron mobility
Solution Approach 1:
The buffer layer is divided into multiple regions with different Fe doping concentrations. The first buffer layer has higher Fe concentration to suppress leakage current, while the second buffer layer has lower Fe concentration to prevent upward diffusion to the 2DEG region. This segmentation allows each region to fulfill its specific function without compromising the other.
Solution Approach 2:
Different regions of the buffer layer are assigned different local properties (Fe doping concentrations) according to their functional requirements. The high-Fe region provides leakage suppression, while the low-Fe region protects the 2DEG from Fe contamination, optimizing both leakage current and electron mobility.
2Reliability
If an AlGaN layer is formed on the Fe-doped buffer layer to prevent Fe diffusion, then Fe diffusion is suppressed, but the crystallinity of the channel layer is degraded
Solution Approach 1:
Instead of changing the material composition (adding AlGaN layer), the invention changes the doping concentration parameter of the existing GaN buffer layer. By adjusting Fe concentration from high in the first buffer layer to low in the second buffer layer, Fe diffusion is suppressed while maintaining good crystallinity and electron mobility.
3Reliability
If the Fe concentration in the buffer layer is increased to compensate donor impurities, then off-state leakage current is reduced, but the on-resistance increases due to Fe diffusion into the 2DEG region
Solution Approach 1:
The buffer layer is segmented into a first buffer layer with high Fe concentration for leakage suppression and a second buffer layer with low Fe concentration to prevent 2DEG degradation. This spatial segmentation allows the system to achieve both low off-state leakage current and low on-resistance simultaneously.
Solution Approach 2:
The second buffer layer with low Fe concentration acts as an intermediary between the high-Fe first buffer layer and the 2DEG region. It serves as a transition zone that prevents Fe from reaching the 2DEG while allowing the first buffer layer to effectively suppress leakage current.
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 effectively reduces Fe diffusion, maintaining good crystallinity and enhancing electron mobility, thereby reducing on-resistance in nitride semiconductor HEMTs.
Implementation Method 1
Fe, however, is likely to diffuse upward in a GaN layer during its growth. Fe is greater in ion radius than Ga.
Implementation Method 2
because the a lattice constant of AlGaN is smaller than the a lattice constant of GaN, it is possible to prevent entry of Fe that is greater in size than Ga and thus to prevent the upward diffusion of Fe
Implementation Method 3
there is the technique of suppressing the off-state leakage current by increasing the resistance of the buffer layer by doping the buffer layer with Fe, which is an acceptor impurity, to compensate the donor
Data Source
AI summary
A semiconductor crystal substrate includes a first buffer layer formed of a nitride semiconductor over a substrate, a second buffer layer formed of a nitride semiconductor on the first buffer layer, a first semiconductor layer formed of a nitride semiconductor on or over the second buffer layer, and a second semiconductor layer formed of a nitride semiconductor on the first semiconductor layer. The Fe concentration of the first buffer layer is higher than the C concentration of the first buffer layer. The C concentration of the second buffer layer is higher than the Fe concentration of the second buffer layer.