GaN Epitaxial Substrate with AlGaN Buffer for Current Collapse Suppression
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Solution Overview
Problem
Current nitride semiconductor HEMT structures using semi-insulating GaN substrates face issues with current collapse due to diffusion of acceptor elements like Fe, Mg, and Zn, which act as electron traps, leading to reduced performance.
Innovation Solution
A semi-insulating free-standing GaN substrate with a dislocation density of 5.0×10^7 cm^-2, doped with Zn, is used in conjunction with a diffusion suppressing AlpGa1-pN buffer layer (0.7≤p≤1) to prevent Zn diffusion into the channel layer, maintaining a Zn concentration of ≤1×10^16 cm^-3, thereby reducing current collapse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a semi-insulating GaN substrate doped with Zn is used to achieve low cost and high quality, then the substrate quality is improved, but Zn diffuses into the channel layer causing current collapse
Solution Approach 1:
An AlN buffer layer is introduced as an intermediary between the Zn-doped semi-insulating GaN substrate and the AlGaN channel layer. This buffer layer acts as a diffusion barrier that prevents Zn atoms from migrating into the channel layer, thereby eliminating the harmful effect of Zn diffusion while maintaining the benefits of using a semi-insulating substrate.
2Reliability
If a diffusion barrier layer is added to prevent Zn diffusion, then current collapse is suppressed, but the device structure becomes more complex
Solution Approach 1:
The buffer layer's composition and thickness are optimized to achieve the necessary diffusion barrier function. By controlling the Al content and thickness parameters of the buffer layer, the patent achieves effective Zn diffusion prevention while keeping the additional structure minimal and manageable.
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
The implementation effectively suppresses current collapse in HEMT elements, enhancing their performance by maintaining low Zn concentration in the channel layer and improving the epitaxial substrate's crystalline quality.
Implementation Method 1
the buffer layer is a diffusion suppressing layer formed of AlpGa1-pN (0.7≤p≤1) having a thickness of 1 nm to 100 nm, and suppresses the diffusion of Zn from the free-standing substrate into the channel layer
Data Source
AI summary
An epitaxial substrate for semiconductor elements is provided which suppresses the occurrence of current collapse. The epitaxial substrate for the semiconductor elements includes: a semi-insulating free-standing substrate formed of GaN doped with Zn; a buffer layer adjacent to the free-standing substrate; a channel layer adjacent to the buffer layer; and a barrier layer provided on an opposite side of the buffer layer with the channel layer therebetween, wherein the buffer layer is a diffusion suppressing layer formed of AlpGa1-pN (0.7≤p≤1) and suppresses diffusion of Zn from the free-standing substrate into the channel layer.