GaN Enhancement-Mode Transistor Gate With Segmented Doping
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Solution Overview
Problem
Gallium nitride (GaN) enhancement mode transistors face high gate leakage issues due to the difficulty in controlling Mg concentration near the gate contact, leading to trade-offs between threshold voltage and leakage current.
Innovation Solution
A method involving a p-doped AlxGayInzN gate layer with a discontinuous growth process, where the Mg concentration is increased above a threshold in the second part to create a self-compensation effect, reducing hole concentration and leakage, while maintaining a high enough concentration for 'normally off' mode operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high active Mg concentration is used in the p-GaN layer to achieve a high threshold voltage, then the threshold voltage is improved, but gate leakage increases
Solution Approach 1:
The p-GaN layer is divided into multiple sub-layers with different Mg concentrations. The lower sub-layer has higher Mg concentration to provide sufficient threshold voltage, while the upper sub-layer has lower Mg concentration to reduce gate leakage. This segmentation allows independent optimization of each sub-layer's doping profile to resolve the contradiction between threshold voltage and gate leakage.
Solution Approach 2:
Different regions of the p-GaN layer are assigned different Mg concentrations based on their functional requirements. The region closer to the AlGaN barrier has higher Mg concentration for threshold control, while the region closer to the metal gate has lower Mg concentration for leakage reduction. This local quality variation optimizes both threshold voltage and gate leakage performance.
2Object-generated harmful factors
If the Mg concentration is reduced to lower gate leakage, then gate leakage is improved, but threshold voltage decreases
Solution Approach 1:
The p-GaN layer is segmented into sub-layers where the lower sub-layer maintains high Mg concentration to ensure adequate threshold voltage, while the upper sub-layer uses lower Mg concentration to minimize gate leakage. This segmentation enables the system to achieve low leakage without sacrificing threshold voltage.
Solution Approach 2:
The Mg concentration parameter is varied through the thickness of the p-GaN layer rather than being uniform. By changing the doping concentration parameter spatially, the invention achieves optimal balance between threshold voltage and gate leakage, resolving the contradiction between these two parameters.
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 allows for a uniform and controllable depletion region at the metal gate interface, significantly reducing gate leakage and enhancing the reliability of GaN enhancement mode transistors.
Implementation Method 1
where the Mg concentration is increased above a threshold in the second part to create a self-compensation effect, reducing hole concentration and leakage
Implementation Method 2
by providing a metal gate layer thereon. This allows for a uniform and controllable depletion region at the metal gate interface
Data Source
Figure 1~2
Figure 3
AI summary
A method for forming a gate of an enhancement-mode transistor comprising: a. providing a p-doped AlxGayInzN gate layer (2), consisting of a first (2a) and a second part (2b) on top of one another, above a p-doped Alx'Gay'Inz'N channel layer (4) of an enhancement-mode transistor under construction, and b. providing a metal gate layer (1) on the top surface of the second part, the metal gate layer being formed of a material such as to form a Schottky barrier with the second part, wherein providing the p-doped AlxGayInzN gate layer comprises the steps of: a1. growing the first part above the p-doped Alx'GayInz'N channel layer of the enhancement-mode transistor under construction, the first part having an average Mg concentration of at most 3x1019 atoms/cm3 and a2. growing a second part having an average Mg concentration higher than 3x1019 atoms/cm3 and having a top surface having a Mg concentration higher than 6x1019 atoms/cm3, on the first part.