III-V HEMT Devices with Segmented GaN Layers for Normally-Off Stability
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Solution Overview
Problem
Semiconductor devices with III-V semiconductors face a tradeoff between achieving stable normally-off operation and reducing on-resistance, as reducing impurity concentration in the p-GaN layer can lead to unstable normally-off operation and increased on-resistance due to electron scattering.
Innovation Solution
The introduction of a middle layer with low impurity concentration and a second layer with a wider band gap forms a heterojunction, where the 2DEG is primarily generated in the middle layer, reducing electron scattering and maintaining stable normally-off operation, and the use of piezoelectric and spontaneous polarization fields offsets each other to suppress unwanted carrier generation at the junction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If impurity concentration in the p-GaN layer is reduced, then on-resistance is reduced, but normally-off operation becomes unstable
Solution Approach 1:
The device is segmented into multiple functional layers: a p-GaN layer for carrier blocking, an intrinsic GaN layer for low-resistance current flow, and an AlGaN layer for potential well formation. This segmentation allows each layer to be optimized independently - the p-GaN layer can maintain higher impurity concentration for stability while the intrinsic layer provides low resistance path for 2DEG electrons.
Solution Approach 2:
The intrinsic GaN layer acts as an intermediary between the p-GaN layer and the AlGaN layer. It receives 2DEG electrons from the potential well and provides a clean, low-impurity pathway for electron transport to the drain, preventing electrons from traversing through the impurity-containing p-GaN layer while maintaining stable normally-off operation.
2Object-affected harmful factors
If impurity concentration in the p-GaN layer is reduced, then electron scattering is reduced, but 2DEG generation becomes uncontrollable
Solution Approach 1:
Different regions of the device are assigned different impurity concentrations according to their specific functions. The p-GaN layer has higher impurity concentration for effective carrier blocking and stable off-state, while the intrinsic GaN layer has extremely low impurity concentration (<1×10^17 cm^-3) to minimize electron scattering and maximize electron mobility in the on-state.
Solution Approach 2:
The impurity concentration parameter is changed across different layers to optimize device performance. The p-GaN layer maintains higher impurity levels for stability, while the intrinsic layer uses near-zero impurity concentration to reduce scattering. This parameter variation resolves the contradiction between scattering reduction and 2DEG control.
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 allows for both stable normally-off operation and reduced on-resistance by minimizing electron scattering and carrier generation, enabling efficient current flow without the need for high impurity concentrations.
Implementation Method 1
a potential well is formed by the p-GaN layer and the n-AlGaN layer at their junction, however, an energy level of conduction band of the potential well is above the Fermi level unless a positive gate voltage is not applied to the gate electrode. Consequently 2DEG (2 Dimensional Electron Gas) is not generated in the potential well while the gate voltage is not being applied to the gate electrode.
Implementation Method 2
the use of piezoelectric and spontaneous polarization fields offsets each other to suppress unwanted carrier generation at the junction
Implementation Method 3
the use of piezoelectric and spontaneous polarization fields offsets each other to suppress unwanted carrier generation at the junction
Data Source
AI summary
A semiconductor device has a stacked structure in which a p-GaN layer, an SI-GaN layer, and an AlGaN layer are stacked, and has a gate electrode that is formed at a top surface side of the AlGaN layer. A band gap of the AlGaN layer is wider than a band gap of the p-GaN layer and the SI-GaN layer. Moreover, impurity concentration of the SI-GaN layer is less than 1×1017 cm−3. Semiconductor devices including III-V semiconductors may have a stable normally-off operation.