E-mode HEMT with Polarization Gradient Barrier
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Solution Overview
Problem
Existing high electron mobility transistors (HEMTs) operate primarily in depletion mode and lack a simple method to transition to enhancement mode, which limits their circuit complexity and performance.
Innovation Solution
The implementation of an enhancement mode HEMT structure by removing the 2DEG under the gate, utilizing a barrier structure with varying polarization and aluminum content gradients, and forming specific layers such as AlGaN and In-based layers to achieve a polarization density gradient, allowing for the creation of a p-doping effect and efficient electron mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional HEMT structure with uniform barrier layers is used, then the device operates in depletion mode with stable 2DEG formation, but it cannot achieve enhancement mode operation and has limited circuit complexity
Solution Approach 1:
The barrier structure is divided into multiple layers (first barrier layer, second barrier layer, third barrier layer) with different Al compositions and polarization characteristics. The second barrier layer specifically has a polarization density gradient in the thickness direction, creating local variations in electrical properties that enable both depletion and enhancement mode operation while maintaining overall device functionality
Solution Approach 2:
The invention changes the polarization parameter by introducing a barrier structure with varying polarization density through the thickness direction. This parameter change in the second barrier layer creates the p-doping effect necessary for enhancement mode operation, transforming the transistor from fixed depletion mode to variable mode operation
2Reliability
If the barrier structure has uniform composition, then the manufacturing process is simple, but electron mobility and breakdown voltage are limited
Solution Approach 1:
The barrier structure is segmented into three distinct layers, each with specific Al composition ranges and functions. This segmentation allows optimization of each layer for specific purposes (2DEG formation, polarization gradient, and stability) while maintaining manufacturability through standardized layer-by-layer fabrication processes
Solution Approach 2:
The invention uses composite AlGaN barrier layers with different Al compositions (first barrier layer: 15-100% Al, second barrier layer: gradient composition, third barrier layer: 0-20% Al). These composite materials provide enhanced electron mobility and breakdown voltage through the synergistic effects of different composition zones
3Ease of operation
If a simple barrier structure is used, then the manufacturing process is easier, but the transistor cannot achieve enhancement mode and has reduced performance
Solution Approach 1:
Instead of adding complex control mechanisms to achieve enhancement mode, the invention inverts the approach by using a polarization density gradient in the barrier layer to naturally create the p-doping effect. This inverted methodology achieves enhancement mode capability through material property design rather than additional structural complexity
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 simplifies HEMT circuits, enhances electron mobility, and increases breakdown voltage by enabling the HEMT to operate in enhancement mode, improving the transistor's performance and reliability.
Implementation Method 1
The polarization of the barrier structure varies in a region corresponding to a gate electrode. The polarization of the second barrier layer varies along a thickness of the second barrier layer.
Implementation Method 2
the barrier structure, in a region corresponding to a region of the channel layer having a depleted 2DEG, has a polarization density gradient that exhibits a p-doping effect
Implementation Method 3
Due to the semiconductor having a large energy band gap, a 2-dimensional electron gas (2DEG) is generated in a semiconductor having a small energy band gap.
Data Source
AI summary
According to an example embodiment, a high electron mobility transistor (HEMT) includes a substrate, a buffer layer on the substrate, a channel layer on the buffer layer, and a barrier structure on the channel layer. The buffer layer includes a 2-dimensional electron gas (2DEG). A polarization of the barrier structure varies in a region corresponding to a gate electrode. The HEMT further includes and the gate electrode, a source electrode, and a drain electrode on the barrier structure.