N-polar HEMT Barrier Segmentation for Conductivity and Breakdown
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Solution Overview
Problem
Current N-polar High Electron Mobility Transistors (HEMTs) face challenges in achieving high channel conductivity and breakdown voltage, limiting their widespread adoption and high-frequency, high-power performance.
Innovation Solution
A method for fabricating N-polar III-Nitride HEMTs with a Nitrogen polar InxAlyGazN barrier layer, inducing a two-dimensional electron gas (2DEG) and using an InAlN cap layer to achieve low sheet resistance and high breakdown voltage, grown using Metal Organic Chemical Vapor Deposition (MOCVD).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional N-polar HEMT structures are used, then device simplicity is maintained, but channel conductivity and breakdown voltage are insufficient
Solution Approach 1:
The barrier layer is segmented into multiple layers with different compositions: an InAlN barrier layer adjacent to the channel layer and an InxAlyGazN barrier layer adjacent to the InAlN barrier layer. This segmentation allows each layer to contribute differently to the overall device performance, with the InAlN layer providing high polarization charge for channel conductivity and the InxAlyGazN layer providing wider bandgap for breakdown voltage enhancement.
Solution Approach 2:
The patent employs a composite barrier structure combining InAlN and InxAlyGazN materials. The InAlN layer provides high spontaneous polarization for strong 2DEG formation, while the InxAlyGazN layer with wider bandgap provides higher breakdown voltage. This composite approach leverages the complementary strengths of different material systems to simultaneously achieve high conductivity and high voltage capability.
2Reliability
If higher indium composition is used in the barrier layer, then channel conductivity increases, but lattice mismatch and dislocation increase
Solution Approach 1:
The patent applies local quality by having different indium compositions in different barrier layers. The InAlN layer adjacent to the channel has higher indium content (x=0.15-0.2) to maximize polarization charge and channel conductivity, while the InxAlyGazN layer has lower indium content to maintain lattice stability and reduce dislocation. Each layer's composition is optimized for its specific function and position in the structure.
Solution Approach 2:
The patent changes the compositional parameters of the barrier layers to optimize performance. By carefully controlling the indium composition x in the range of 0.15-0.2 in the InAlN layer and using appropriate Al and Ga compositions in the InxAlyGazN layer, the patent achieves the desired balance between polarization charge density and lattice matching, thereby optimizing channel conductivity while maintaining structural stability.
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
The approach results in HEMTs with high channel conductivity, low gate leakage, and enhanced breakdown voltage, improving high-frequency and high-power performance, with output power density of at least 3.34 W/mm and power added efficiency (PAE) of at least 39% at 4 GHz.
Implementation Method 1
a compositional difference between the barrier layer and the channel layer results in a two-dimensional electron gas (2DEG) being induced in the channel layer
Implementation Method 2
These devices are typically grown epitaxially using growth techniques, such as Metal Organic Chemical Vapor Deposition (MOCVD)
Implementation Method 3
N-polar describes devices wherein the epitaxial layers are epitaxially grown in a [0 0 0 −1] direction of the wurtzite crystal
Data Source
AI summary
A method for growing high mobility, high charge Nitrogen polar (N-polar) or Nitrogen face (In,Al,Ga)N/GaN High Electron Mobility Transistors (HEMTs). The method can provide a successful approach to increase the breakdown voltage and reduce the gate leakage of the N-polar HEMTs, which has great potential to improve the N-polar or N-face HEMTs' high frequency and high power performance.