GaN Transistor Buffer Structure for Uniform Carbon Doping
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Solution Overview
Problem
Gallium nitride (GaN) transistors face issues with current collapse due to non-uniform intrinsic carbon doping, which affects performance and increases production costs, and the epitaxial deposition process temperature requirements compromise material quality, while exposed AlGaN layers lead to oxidation and surface micro-pitting.
Innovation Solution
The implementation of a dual superlattice buffer structure with extrinsic carbon doping using ethene as a carbon source gas, allowing for uniform carbon distribution and higher temperature epitaxial growth, along with a silicon nitride cap layer to prevent oxidation and improve surface integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intrinsic carbon doping is increased to improve current collapse performance, then current collapse performance is improved, but epitaxial deposition process temperature must be decreased which adversely affects the quality of the deposited GaN material
Solution Approach 1:
The patent changes the doping mechanism from intrinsic to extrinsic carbon doping, allowing carbon incorporation without reducing epitaxial deposition temperature. This parameter change in the doping method enables simultaneous achievement of improved current collapse performance and maintained material quality.
Solution Approach 2:
The patent introduces an intermediary extrinsic carbon source that enables carbon doping through a different mechanism than intrinsic doping. This intermediary approach allows carbon to be incorporated into the GaN lattice without requiring temperature reduction, thus resolving the contradiction between doping effectiveness and material quality.
2Reliability
If intrinsic carbon doping is used to improve current collapse performance, then current collapse performance is improved, but carbon doping is not uniform across the processed wafer leading to varying performance and reduced production yield
Solution Approach 1:
The patent changes from intrinsic to extrinsic carbon doping, which fundamentally alters how carbon is incorporated into the GaN layer. Extrinsic doping provides uniform carbon distribution across the entire wafer surface, eliminating the location-dependent variability inherent in intrinsic doping methods.
3Quantity of substance
If epitaxial deposition is performed at lower temperature to increase intrinsic carbon doping, then carbon doping level is increased, but the quality of deposited GaN material deteriorates
Solution Approach 1:
The patent introduces an intermediary extrinsic carbon source that enables carbon incorporation through a different mechanism. This intermediary approach allows carbon to be added to the GaN layer without requiring temperature reduction, thus maintaining both high carbon doping levels and high material quality.
Solution Approach 2:
The patent changes the fundamental parameter of the doping mechanism from intrinsic to extrinsic, allowing carbon doping to occur at higher temperatures. This parameter change decouples the relationship between temperature and carbon doping level, enabling independent optimization of both.
4Device complexity
If exposed AlGaN layer is left without protection, then device structure is simplified, but oxidation and surface micro-pitting occur causing leakage performance issues and early product failures
Solution Approach 1:
The patent applies a thin silicon nitride cap layer that serves as a protective barrier during processing. This disposable-like protective layer prevents oxidation and surface damage, and can be removed or integrated into subsequent processing steps without adding significant complexity to the overall device structure.
Solution Approach 2:
The silicon nitride cap layer creates an inert protective environment over the exposed AlGaN surface, preventing harmful oxidation reactions. This inert barrier approach protects the sensitive semiconductor surface without requiring complex active protection systems.
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 enhances current collapse performance, achieves uniform carbon doping across the wafer, reduces production costs, and mitigates leakage issues, resulting in improved GaN transistor reliability and yield.
Implementation Method 1
Epitaxial deposition of buffer layers and some GaN transistors involves intrinsic carbon doping due to use of a metal organic source
Implementation Method 2
performing an epitaxial deposition process that deposits at least one layer of the buffer structure using an extrinsic carbon source gas
Data Source
AI summary
Fabrication methods and gallium nitride transistors, in which an electronic device includes a substrate, a buffer structure, a hetero-epitaxy structure over the buffer structure, and a transistor over or in the hetero-epitaxy structure. In one example, the buffer structure has an extrinsically carbon doped gallium nitride layer over a dual superlattice stack or over a multilayer composition graded aluminum gallium nitride stack, and a silicon nitride cap layer over the hetero-epitaxy structure.