GaN HEMT Normally-Off Operation via P-Type Layer Segmentation
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Solution Overview
Problem
GaN-based HEMTs typically operate in a normally-on mode due to two-dimensional electron gas formation, leading to potential current leakage issues, and there is a need for a method to control electric charge between the source and drain to achieve a normally-off operation for safety and efficiency.
Innovation Solution
The structure includes an AlN layer and n-type GaN layers with specific doping and thicknesses, along with a p-type GaN layer and silicon oxide film, to control current flow and enable normally-off operation by managing carrier density distribution, using HVPE and MOCVD methods for layer formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a GaN-based HEMT is designed with a simple structure to reduce manufacturing complexity, then manufacturing cost and time are reduced, but the device cannot achieve normally-off operation and suffers from current leakage
Solution Approach 1:
The device is segmented into multiple functional layers including a first compound semiconductor layer (n-type GaN), a second compound semiconductor layer (p-type GaN), and a third compound semiconductor layer (n-type GaN with higher doping concentration). This segmentation allows each layer to perform specific functions: the first layer provides high electron mobility, the second layer enables normally-off operation through hole accumulation, and the third layer enhances current control. By dividing the device into these distinct segments, the patent achieves normally-off operation without significantly complicating the manufacturing process.
Solution Approach 2:
Different regions of the device are assigned different doping concentrations and types to create local quality variations. The first compound semiconductor layer has a doping concentration of 1×10^17 to 1×10^18 atoms/cm³, while the third layer has a higher doping concentration of 1×10^18 to 1×10^19 atoms/cm³. The second layer is p-type with doping concentration of 1×10^17 to 1×10^18 atoms/cm³. These localized quality differences enable precise control of carrier distribution, allowing normally-off operation while maintaining overall device performance and manufacturing feasibility.
2Productivity
If the device structure is simplified to reduce manufacturing steps, then production efficiency increases, but control over carrier density distribution deteriorates
Solution Approach 1:
The patent utilizes parameter changes in doping concentration to achieve precise carrier density control. The first compound semiconductor layer uses doping concentration of 1×10^17 to 1×10^18 atoms/cm³, the second layer uses 1×10^17 to 1×10^18 atoms/cm³, and the third layer uses 1×10^18 to 1×10^19 atoms/cm³. By carefully controlling these doping parameters during epitaxial growth, the device achieves the desired carrier density distribution for normally-off operation while maintaining a relatively simple manufacturing process that can be integrated into existing production lines.
3Reliability
If a p-type layer is introduced to achieve normally-off operation, then current control and safety are improved, but device structure and manufacturing complexity increase
Solution Approach 1:
The device employs a composite structure combining n-type GaN layers with a p-type GaN layer. The first compound semiconductor layer (n-type GaN) provides high electron mobility, the second layer (p-type GaN) enables normally-off operation through hole accumulation that depletes electrons from the channel, and the third layer (n-type GaN with higher doping) enhances current control. This composite material approach achieves reliable normally-off operation while keeping each individual layer relatively simple in composition, facilitating manufacturing.
4Reliability
If multiple doped layers are added to control current flow, then electrical performance and reliability are improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent defines specific doping concentration ranges for each layer to balance performance and manufacturability. The first compound semiconductor layer uses 1×10^17 to 1×10^18 atoms/cm³, the second layer uses 1×10^17 to 1×10^18 atoms/cm³, and the third layer uses 1×10^18 to 1×10^19 atoms/cm³. These parameter specifications provide clear manufacturing targets while allowing sufficient process window for conventional epitaxial growth techniques, achieving reliable current control without excessive manufacturing precision requirements.
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 effectively suppresses current collapse and ensures a high on-resistance when the device is on, while maintaining a low off-resistance, allowing for controlled current flow and improved reliability, particularly in high-voltage applications.
Implementation Method 1
a p-body layer is formed at a part contacting with the p-type layer of the lower layer due to dispersion of Mg from the p-type layer
Implementation Method 2
an AlGaN layer and a GaN layer are formed over a substrate through crystal growth
Data Source
AI summary
An n-type GaN layer (3), a GaN layer (7) formed over the n-type GaN layer (3), an n-type AlGaN layer (9) formed over the GaN layer (7), a gate electrode (15) and a source electrode (13) formed over the n-type AlGaN layer (9), a drain electrode (14) formed below the n-type GaN layer (3), and a p-type GaN layer (4) formed between the GaN layer (7) and the drain electrode (14) are provided.