GaN HEMT Gate AlN Layer for Normally-Off Operation
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Solution Overview
Problem
AlGaN/GaN-HEMTs face challenges in achieving normally-off operation while maintaining high withstanding voltage and output, due to high contact resistances and dense two-dimensional electron gas.
Innovation Solution
Incorporating a nitride-polar surface with a GaN layer and a crystalline AlN layer under the gate electrode, which suppresses two-dimensional electron gas generation by raising the energy level of the conduction band, allowing for a normally-off operation without modifying the transistor design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an AlGaN/GaN-HEMT with inverted HEMT structure is used, then contact resistance is reduced, but normally-off operation cannot be achieved due to dense two-dimensional electron gas
Solution Approach 1:
The patent applies local quality by creating a heterogeneous structure where an AlN layer is positioned specifically under the gate electrode region, while other regions maintain the AlGaN/GaN HEMT structure. This localized modification suppresses two-dimensional electron gas generation only in the critical gate area, enabling normally-off operation without compromising the overall device performance and contact characteristics.
Solution Approach 2:
The AlN layer serves as an intermediary element between the gate electrode and the AlGaN/GaN HEMT structure. It mediates the electron transport by raising the conduction band energy level, which suppresses the formation of dense two-dimensional electron gas while maintaining electrical contact. This intermediary layer resolves the contradiction by providing a controlled barrier that enables normally-off operation.
2Ease of operation
If a semiconductor layer is provided only under the gate electrode, then two-dimensional electron gas generation is suppressed, but device complexity increases
Solution Approach 1:
The patent minimizes device complexity by applying the semiconductor layer modification locally only under the gate electrode rather than throughout the entire device structure. This localized approach achieves the desired normally-off operation while keeping the manufacturing process and overall device structure as simple as possible.
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 configuration achieves a normally-off operation with reduced contact resistance, higher withstanding voltage, and higher output, while maintaining a cost-effective manufacturing process.
Implementation Method 1
a semiconductor layer provided on the first nitride semiconductor layer and only under the gate electrode, and exhibiting a polarization
Data Source
AI summary
A semiconductor device includes a substrate; a first nitride semiconductor layer provided over the substrate and having a nitride-polar surface; a gate electrode provided over the first nitride semiconductor layer; and a semiconductor layer provided on the first nitride semiconductor layer and only under the gate electrode, and exhibiting a polarization.