HEMT Epitaxial Buffer Structure Using Polarization-Doped p-i-n Stacks
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Solution Overview
Problem
Existing methods for manufacturing GaN-based epitaxial structures for high-electron-mobility transistors (HEMTs) face challenges such as high background electron concentration, low resistance, increased defects and impurities, and low reproducibility. Additionally, conventional methods require precise control of epitaxial growth parameters and can lead to electrical leakage and reduced device reliability.
Innovation Solution
The proposed solution involves an epitaxial structure for HEMTs comprising a substrate, nucleation layer, buffer layered unit, channel layer, and barrier layer. The buffer layered unit includes a plurality of p-i-n heterojunction stacks with graded AlGaN layers, formed using polarization doping to control aluminum and gallium content gradients, thereby reducing background carrier concentration and enhancing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods control epitaxial growth parameters to increase p-type dopant and defects, then background electron concentration is reduced, but the amount of defects and impurities increases greatly
Solution Approach 1:
The patent changes the doping mechanism from conventional p-type dopants to polarization doping by controlling the aluminum content gradient in AlGaN layers. This parameter change eliminates the need for traditional dopants while achieving the desired carrier concentration control, thus reducing both background electrons and defect formation
Solution Approach 2:
The patent uses composite AlGaN layers with varying aluminum compositions (different x values in AlxGa1-xN) to create the buffer layer. This composite structure enables polarization doping where the polarization effect itself provides the carrier control mechanism, avoiding the introduction of harmful impurities while achieving reliable electrical properties
2Reliability
If metals are introduced during epitaxial growth to generate defects and electron holes, then resistance increases, but metals cause contamination and lower electron mobility
Solution Approach 1:
The patent replaces the mechanical/chemical doping approach (introducing metal atoms during growth) with a polarization-based mechanism. The electric field and polarization charges inherent in the AlGaN/GaN heterostructure provide the necessary carrier control without introducing foreign metal contaminants, thus maintaining high electron mobility while achieving the desired resistance characteristics
3Reliability
If conventional methods are used to manufacture GaN-based epitaxial structure, then background electron concentration is high, but reproducibility is low due to high dependency on equipment control
Solution Approach 1:
The patent employs self-service through polarization doping where the material composition gradient itself generates the doping effect. The aluminum content gradient in AlGaN automatically creates the polarization charges that control carrier concentration, eliminating the need for complex external doping processes and equipment control, thereby achieving both low background electron concentration and high reproducibility
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 results in a high-quality epitaxial structure with reduced electrical leakage, improved resistance, and enhanced reproducibility, leading to better performance and reliability of HEMT devices.
Implementation Method 1
formed using polarization doping to control aluminum and gallium content gradients, thereby reducing background carrier concentration and enhancing resistance
Data Source
AI summary
An epitaxial structure for a high-electron-mobility transistor includes a substrate, a nucleation layer, a buffer layered unit, a channel layer, and a barrier layer sequentially stacked on one another in such order. The buffer layered unit includes a plurality of p-i-n heterojunction stacks. Each of the p-i-n heterojunction stacks includes p-type, i-type, and n-type layers which are made of materials respectively represented by chemical formulas of AlxGa(1-x)N, AlyGa(1-y)N, and AlzGa(1-z)N. For each of the p-i-n heterojunction stacks, x decreases and z increases along a direction away from the nucleation layer, and y is consistent and ranges from 0 to 0.7.