InAlGaN Cap Layer Reduces Parasitic Resistance in GaN HEMTs
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Solution Overview
Problem
High-frequency characteristics of AlGaN/GaN heterojunction field effect transistors are hindered by large parasitic resistance due to potential barriers at the InAlGaN/AlGaN interface, which increases ohmic contact resistance and degrades device performance.
Innovation Solution
The Al composition in the AlGaN layer is optimized to ensure continuous lower ends of the conduction bands between the AlGaN and InAlGaN layers, reducing parasitic resistance by minimizing the potential barrier and enhancing lattice matching and polarization, thereby improving high-frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a cap layer made of GaN is sandwiched between the electrode and the AlGaN to reduce contact resistance, then ohmic contact resistance is reduced, but a potential barrier is caused between the GaN and the AlGaN due to polarization difference, increasing parasitic resistance
Solution Approach 1:
The patent changes the compositional parameters of the cap layer from pure GaN to InAlGaN with specific In and Al composition ratios. By adjusting these parameters, the polarization characteristics are modified to reduce the potential barrier at the hetero interface while maintaining low contact resistance, thus resolving the contradiction between reducing ohmic contact resistance and minimizing parasitic resistance
Solution Approach 2:
The patent uses a composite InAlGaN material for the cap layer instead of a single material. This composite structure allows simultaneous optimization of multiple properties: the In component reduces the potential barrier through polarization matching, while the Al component maintains the necessary band gap and lattice matching with AlGaN, thereby achieving both low contact resistance and low parasitic resistance
2Reliability
If the Al composition in the AlGaN layer is increased to improve lattice matching and polarization, then high-frequency characteristics are improved, but the band gap increases making ohmic contact formation more difficult
Solution Approach 1:
The InAlGaN cap layer acts as an intermediary between the high-Al composition AlGaN electron supply layer and the metal electrode. It mediates the contradiction by providing a transition zone with optimized polarization characteristics that reduce the potential barrier, enabling good ohmic contact formation even when the underlying AlGaN layer has high Al composition for improved high-frequency performance
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 results in significantly reduced parasitic resistance, allowing for improved high-frequency performance and lower ohmic contact resistance, enhancing the overall transistor characteristics.
Implementation Method 1
a strong polarization electric field formed on the (0001) plane, so as to generate what is called a two-dimensional electron gas
Implementation Method 2
lower ends of conduction bands of the nitride semiconductor layer and the InxAlyGa1-x-yN layer are substantially continuous on an interface therebetween
Implementation Method 3
electrons are stored in a high concentration in the vicinity of the hetero junction interface within the GaN film owing to a strong polarization electric field formed on the (0001) plane
Implementation Method 4
a GaN-based material is high at what is called saturated drift velocity, and has electronic velocity twice or more as high as that of a GaAs-based material currently widely used as a material for a high-frequency transistor in a high electric field region
Data Source
AI summary
A field effect transistor includes a nitride semiconductor layer; an InxAlyGa1-x-yN layer (wherein 0<x<1, 0<y<1 and 0<x+y<1) formed on the nitride semiconductor layer; and a source electrode and a drain electrode formed on and in contact with the InxAlyGa1-x-yN layer. The lower ends of the conduction bands of the nitride semiconductor layer and the InxAlyGa1-x-yN layer are substantially continuous on the interface therebetween.