GaN HFET Superlattice Buffer Al Composition
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Solution Overview
Problem
The formation of a two-dimensional hole gas in nitride semiconductor devices leads to increased leakage current due to the mismatch in lattice constants and stress between AlGaN and GaN layers, which is not effectively addressed by existing buffer layer structures.
Innovation Solution
A nitride semiconductor structure is developed with a superlattice buffer layer composed of alternately stacked high-Al content AlxGa1-xN and low-Al content AlyGa1-yN layers, where the channel layer is formed by stacking AlzGa1-zN and GaN layers with the Al composition of the AlzGa1-zN layer matching the average Al composition of the superlattice buffer layer, reducing strain and suppressing the formation of a two-dimensional hole gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a buffer layer composed of alternately stacked AlGaN layers with different Al compositions is used, then the propagation of dislocation defects is suppressed, but a two-dimensional hole gas is formed causing increased leakage current
Solution Approach 1:
The invention changes the Al composition parameter in the buffer layer structure. By setting the Al composition in the AlGaN barrier layer to be equal to or higher than the average Al composition in the superlattice buffer layer, the patent prevents the formation of two-dimensional hole gas while maintaining the dislocation suppression effect of the superlattice structure.
Solution Approach 2:
The invention uses a composite structure consisting of a superlattice buffer layer (alternating high-Al and low-Al content AlGaN layers) combined with a barrier layer having specific Al composition. This composite material approach allows simultaneous achievement of dislocation suppression and prevention of hole gas formation.
2Reliability
If the Al composition of the AlGaN barrier layer is lower than the average Al composition of the superlattice buffer layer, then the two-dimensional electron gas is formed, but a two-dimensional hole gas is also formed at the interface
Solution Approach 1:
The invention establishes a specific parameter relationship where the Al composition in the barrier layer (x) must be equal to or greater than the average Al composition in the superlattice buffer layer. This parameter constraint prevents the formation of two-dimensional hole gas while allowing proper electron gas formation for device operation.
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 reduces leakage current by compensating for the two-dimensional hole gas formed between the superlattice buffer layer and the GaN layer, improving the device's properties by maintaining a consistent lattice constant and minimizing strain-induced defects.
Implementation Method 1
the Al composition of the AlzGa1-zN layer is the same as the average Al composition of the superlattice buffer layer... maintaining a consistent lattice constant and minimizing strain-induced defects
Implementation Method 2
compensating for the two-dimensional hole gas formed between the superlattice buffer layer and the GaN layer... minimizing strain-induced defects
Implementation Method 3
the Al composition of the AlzGa1-zN layer is the same as the average Al composition of the superlattice buffer layer... compensating for the two-dimensional hole gas... minimizing strain-induced defects
Data Source
AI summary
According to this GaN-based HFET, resistivity ρ of a semi-insulating film forming a gate insulating film is 3.9×109Ωcm. The value of this resistivity ρ is a value derived when the current density is 6.25×10−4 (A/cm2). By inclusion of the gate insulating film by a semi-insulating film having a resistivity ρ=3.9×109Ωcm, a withstand voltage of 1000 V can be obtained. Meanwhile, the withstand voltage abruptly drops as the resistivity of the gate insulating film exceeds 1 ×1011Ωcm, and the gate leak current increases when the resistivity of the gate insulating film drops below 1 ×107Ωcm.