HEMT Gate Structure With Depleted Region for Low Leakage
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Solution Overview
Problem
HEMT devices based on AlGaN/GaN heterojunctions suffer from leakage current issues due to defects and doping concentration variations, leading to malfunctions and shifts in switch-on threshold voltage, particularly affecting the normally-off mode operation.
Innovation Solution
The HEMT device incorporates a functional region with opposite conductivity type to the channel modulating region, along with a passivation layer and specific gate contact arrangements, to reduce lateral leakage current by creating a depleted region that electrically insulates the gate from sidewall defects, and a second gate contact region to enhance field control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a p-GaN channel modulating region is formed to achieve normally-off operation, then the device can be enhanced-mode, but leakage current increases due to defects and doping variations
Solution Approach 1:
An intrinsic or lightly-doped GaN layer is introduced as an intermediary between the p-GaN gate and the n-AlGaN barrier layer. This intermediate layer acts as a buffer that reduces the impact of defects and doping variations in the p-GaN region, thereby suppressing leakage current while maintaining normally-off operation capability
Solution Approach 2:
The doping concentration in the channel modulating region is optimized to balance between achieving sufficient hole concentration for normally-off operation and minimizing leakage current. By carefully controlling the doping parameters, the device achieves reliable enhancement-mode operation with reduced leakage
2Device complexity
If the gate structure is simplified, then manufacturing complexity is reduced, but control over the 2DEG becomes less effective
Solution Approach 1:
The gate structure employs regions with different doping concentrations and material compositions tailored to specific functional requirements. The channel modulating region has optimized local properties for effective 2DEG control, while maintaining an overall simplified structure that is manufacturable
3Measurement precision
If doping concentration in the channel modulating region is increased to improve normally-off characteristics, then switch-on threshold control improves, but leakage current increases due to defects
Solution Approach 1:
The intrinsic or lightly-doped GaN layer serves as a mediator that allows sufficient hole concentration in the p-GaN gate for threshold voltage control while preventing direct interaction between high-doping regions and defects, thereby suppressing leakage current
Solution Approach 2:
The doping concentration profile is optimized with a gradient or stepped structure, where the channel modulating region has controlled doping levels that balance threshold voltage control capability with leakage suppression
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 significantly reduces gate leakage current, ensuring a low leakage current and improved reliability of the normally-off HEMT device by maintaining a reverse bias condition at the junction and reducing surface electronic states on the sidewalls.
Implementation Method 1
creating a depleted region that electrically insulates the gate from sidewall defects
Implementation Method 2
maintaining a reverse bias condition at the junction
Implementation Method 3
passivation layer and specific gate contact arrangements, to reduce lateral leakage current by creating a depleted region
Implementation Method 4
a conductive channel is based on the formation of high mobility 2-Dimensional Electron Gas (2DEG) layers at a heterojunction, i.e., at the interface between semiconductor materials with different bandgap
Data Source
AI summary
The HEMT device has a body including a heterostructure configured to generate a 2-dimensional charge-carrier gas; and a gate structure which extends on a top surface of the body and is biasable to electrically control the 2-dimensional charge-carrier gas. The gate structure has a channel modulating region of semiconductor material; a functional region of semiconductor material; and a gate contact region of conductive material. The functional region and the gate contact region extend on a top surface of the channel modulating region and the gate contact region is arranged laterally with respect to the functional region. The channel modulating region has a different conductivity type with respect to the functional region.