Double Graded Back Barrier HEMT Structure for Electron Confinement
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Solution Overview
Problem
Next-generation high-charge high-electron-mobility devices, such as HEMTs, suffer from elevated leakage current due to insufficient electron confinement, particularly in ScAlN-based devices, which results in higher buffer leakage compared to AlGaN-based GaN HEMTs, reducing RF efficiency and increasing power loss.
Innovation Solution
The implementation of a pair of continuously graded pseudomorphic back barrier layers, where one layer is graded towards a Group III Nitride alloy from a buffer material and the other from a channel material, creating a quasi-field that enhances electron confinement by increasing the conduction band slope without forming a parasitic 2DEG, along with compensation doping to manage the quasi-field generated by changing polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single back barrier layer with fixed Al concentration is used, then the structure is simple to manufacture, but electron confinement is insufficient leading to high buffer leakage
Solution Approach 1:
The single back barrier layer is segmented into multiple back barrier layers with different Al concentrations. This segmentation creates a graded structure that improves electron confinement by forming a more effective potential barrier, while each individual layer remains manufacturable using standard epitaxial growth techniques.
Solution Approach 2:
Different regions of the back barrier structure are assigned different Al concentrations tailored to local requirements. The graded composition creates locally optimized barrier properties that enhance electron confinement at critical interfaces while maintaining manufacturability through controlled composition gradients.
2Reliability
If the Al concentration in back barrier is increased to improve electron confinement, then buffer leakage is reduced, but parasitic 2DEG formation increases
Solution Approach 1:
The Al concentration parameter is continuously varied across the back barrier structure rather than maintained at a fixed value. This parameter change creates a graded composition that optimizes the balance between buffer leakage control and parasitic 2DEG suppression by adjusting the barrier slope and polarization field distribution.
Solution Approach 2:
The back barrier structure employs a dynamic composition gradient rather than a static uniform composition. This dynamic approach allows the barrier properties to adapt spatially, creating an optimal balance between confinement and parasitic 2DEG prevention through the continuous variation of Al concentration.
3Loss of energy
If a graded back barrier structure is implemented to improve electron confinement, then RF efficiency is enhanced, but manufacturing precision requirements increase
Solution Approach 1:
The continuous variation of Al concentration parameters throughout the back barrier structure creates a graded profile that improves RF efficiency by optimizing electron confinement. The gradual parameter transition reduces abrupt interfaces, thereby relaxing manufacturing precision requirements compared to sharp-step structures.
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 significantly improves electron confinement, reduces parasitic 2DEG formation, and increases the tolerance for heterostructure dimensions, leading to enhanced RF efficiency and reduced power loss in high-electron-mobility devices.
Implementation Method 1
compensation doping to manage the quasi-field generated by changing polarization
Implementation Method 2
The larger the in-plane lattice mismatch, the smaller the critical thickness of the epitaxial layer
Implementation Method 3
When an epitaxial layer is grown on a crystalline substrate or on one or more epitaxial layers with a defined crystallinity, the in-plane lattice of the epitaxial layer will initially conform to match the in-plane lattice constant of the underlying material
Data Source
AI summary
A high electron mobility heterostructure and a method of fabricating the heterostructure, wherein the high electron mobility heterostructure comprises a substrate, a buffer on the substrate, a doped charge compensation layer on the buffer, a double continuous grade barrier on the doped charge compensation layer having increasing polarization charge and decreasing polarization charge, a channel on the double continuous grade barrier, and a charge generation layer on the channel. The method comprises forming a substrate, forming a buffer on the substrate, forming a doped charge compensation layer on the buffer, forming a double continuous grade barrier on the doped charge compensation layer, forming a channel on the double continuous grade barrier, and forming a charge generation layer on the channel.