GaN Epitaxial Substrate With Fe Diffusion Barrier for 2DEG Mobility
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Solution Overview
Problem
Current GaN epitaxial substrates for GaN-HEMTs face challenges in preventing the diffusion of Fe, which degrades electron mobility and hinders high electron mobility operation due to Fe's ability to diffuse into the 2DEG region, leading to performance deterioration.
Innovation Solution
A GaN epitaxial substrate with a steep concentration gradient of Fe and a C-containing layer or Fe diffusion-restricting layer is developed, where the Fe concentration is significantly reduced in the 2DEG region through precise control of Fe distribution and incorporation of a C-containing layer to inhibit Fe movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Fe is doped into the GaN substrate to make it semi-insulating, then the substrate's semi-insulating properties are improved, but Fe diffuses into the 2DEG region causing electron mobility deterioration
Solution Approach 1:
A C-containing layer is introduced as an intermediary barrier between the Fe-doped GaN substrate and the undoped GaN buffer layer. This carbon-containing layer acts as a diffusion barrier that blocks Fe atoms from migrating into the 2DEG region while allowing the substrate to maintain its semi-insulating properties through Fe doping.
Solution Approach 2:
The patent creates a composite structure combining Fe-doped GaN substrate, C-containing layer, and undoped GaN buffer layer. This multi-layer composite structure leverages the semi-insulating properties of Fe-doped GaN while using the C-containing layer to prevent harmful Fe diffusion, thus resolving the contradiction between achieving semi-insulating properties and preventing Fe diffusion.
2Object-generated harmful factors
If the GaN buffer layer is grown at lower temperature to restrict Fe diffusion, then Fe diffusion is reduced, but manufacturing complexity increases due to temperature control constraints
Solution Approach 1:
The C-containing layer is formed in advance during the epitaxial growth process, before the undoped GaN buffer layer is grown. This preliminary action of incorporating carbon into the layer structure creates a built-in diffusion barrier that passively restricts Fe diffusion without requiring complex temperature control during subsequent growth stages.
Solution Approach 2:
The patent changes the chemical composition parameter by introducing carbon into the GaN buffer layer structure. This parameter change creates a C-containing layer with different diffusion characteristics that naturally blocks Fe atoms, avoiding the need for complex temperature control parameters to achieve the same diffusion restriction.
3Reliability
If Fe concentration is maintained in the GaN buffer layer to ensure semi-insulating properties, then semi-insulating performance is improved, but electron mobility in the 2DEG region deteriorates due to Fe presence
Solution Approach 1:
The patent segments the GaN buffer layer into distinct regions: an Fe-doped region adjacent to the substrate that provides semi-insulating properties, a C-containing layer that acts as a diffusion barrier, and an undoped region that maintains high electron mobility for the 2DEG. This segmentation allows each region to fulfill its specific function without compromising the others.
Solution Approach 2:
The patent applies local quality by having different Fe concentrations in different regions of the buffer layer. The region adjacent to the substrate has high Fe concentration for semi-insulating properties, while the region near the 2DEG has low or zero Fe concentration for high electron mobility, with the C-containing layer creating a sharp transition between these local qualities.
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 restricts Fe diffusion to the 2DEG region, maintaining high electron mobility and improving the substrate's semi-insulating properties, thereby enhancing the performance and design flexibility of GaN-HEMTs while reducing manufacturing costs.
Implementation Method 1
a concentration gradient of Fe in a [0001] axis direction is steep, and a C-containing layer having a C concentration of 1×10^16 to 1×10^18 atoms/cm³ is present in a [0001] axis direction relative to the Fe-doped layer
Data Source
AI summary
A GaN epitaxial substrate contains a GaN substrate and a GaN buffer layer epitaxially grown on the GaN substrate. The GaN epitaxial substrate includes a point A and a point B which is positioned on a straight line parallel to a [0001] axis passing through the point A, the point B being present in a [0001] axis direction relative to the point A, the point A is present in the GaN substrate or the GaN buffer layer, the point B is present in the GaN buffer layer, a ratio ([Fe]B/[Fe]A) is 1/100, [Fe]A being a Fe concentration of the point A and [Fe]B being a Fe concentration of the point B, and a distance between the point A and the point B is 0.2 μm or less.