AlN HEMT Interface Grading to Suppress 2DHG Coulomb Drag
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Solution Overview
Problem
High-density two-dimensional hole gas (2DHG) generation at the GaN/AlN interface in nitride-based high electron mobility transistors (HEMTs) leads to coulomb drag on the two-dimensional electron gas (2DEG) layer, reducing mobility due to large negative polarization charge.
Innovation Solution
An AlN buffer layer with an AlGaN composition change layer inserted at the GaN/AlN interface, where the Al composition gradually changes from the AlN buffer layer to the GaN channel layer, reducing the generation of 2DHG and alleviating coulomb drag on the 2DEG layer, and preventing quality deterioration of the GaN channel layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an AlN buffer layer is used in the Al1-x-yGaxInyN/GaN/AlN structure, then thermal conductivity and physical properties are improved, but a high-density two-dimensional hole gas (2DHG) is generated due to large negative polarization charge on the GaN/AlN interface, which lowers mobility of the 2DEG layer
Solution Approach 1:
An AlGaN graded composition change layer is inserted between the AlN buffer layer and the GaN channel layer to serve as an intermediary. This layer gradually transitions the aluminum composition from high (near AlN) to low (near GaN), mediating the interface between the two materials. The graded layer reduces the abrupt polarization charge accumulation that occurs at sharp interfaces, thereby suppressing 2DHG generation while maintaining the thermal conductivity benefits of the AlN buffer layer.
Solution Approach 2:
The aluminum composition parameter (x in AlxGa1-xN) is continuously changed across the graded layer, transitioning from approximately x=1 (AlN) at the buffer layer interface to x=0 (GaN) at the channel layer interface. This parameter change creates a gradual composition profile that reduces the abruptness of the interface, thereby reducing polarization charge density and suppressing 2DHG generation while preserving the thermal management advantages of the AlN buffer layer.
2Temperature
If a GaN/AlN interface is formed with high AlN content, then thermal management is improved, but compressive stress is generated that deteriorates the quality of the GaN channel layer
Solution Approach 1:
The AlGaN graded composition change layer acts as a stress-mediating intermediary between the AlN buffer layer and the GaN channel layer. By gradually transitioning the aluminum content, this intermediate layer reduces the lattice mismatch and compressive stress that would otherwise be directly transmitted to the GaN channel layer, thereby preserving channel layer quality while maintaining the thermal management benefits of the AlN buffer layer.
Solution Approach 2:
The gradual change in aluminum composition parameter across the graded layer creates a progressive transition in lattice constant, reducing the abrupt lattice mismatch between AlN and GaN. This parameter gradient distributes the compressive stress more evenly and reduces peak stress concentrations, preventing dislocation formation and maintaining high crystalline quality in the GaN channel layer.
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 enhances the mobility of the 2DEG layer by suppressing 2DHG generation and maintaining high-quality GaN channel layer crystallinity, suitable for high-power and high-frequency electronic applications.
Implementation Method 1
a large negative polarization charge on an GaN/AlN interface, which has an influence of a coulomb drag on a 2DEG layer
Implementation Method 2
performing an in-situ process in a metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) equipment
Implementation Method 3
performing an in-situ process in a metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) equipment
Data Source
AI summary
The present invention relates to a method of manufacturing an AlN-based transistor. An AlN-based high electron mobility transistor (HEMT) element according to the present invention may use an AlN buffer layer, and include an AlGaN composition change layer inserted into a GaN/AlN interface to remove or suppress a degree of generation of a two-dimensional hole gas (2DHG), thereby decreasing an influence of a coulomb drag on a two-dimensional electron gas (2DEG) layer and improving mobility of a two-dimensional electron gas (2DEG).